In the good old days, people would greet vendorswith a friendly smile.The iceman, postman, milk-man and breadman were typical. Gender neverseemed to be an issue. Firemen respondedpromptly, policemen were ever present, and anendless list of servicemen were available to solvedaily problems, including those related to theGMC Motorhome.

Point in fact.A service manager in Billings,Montana confirmed my suspicion that a “click-ing” constant velocity (CV) joint needed to bereplaced. Since all the service bays were busy, hesuggested that new components be obtained fromthe parts counter in the interim.At lunch break, amechanic would probably be available.

A courteous partsperson identified the GMCMotorhome part number by gazing at a spot onthe ceiling. She also suggested a replacement dustcover, citing a different GMC Motorhome partnumber from the same mysterious source. Howdid she know? It seems there had been severalintensive GMC Motorhome parts seminars, andshe had retained the vital group categories ofinformation. Besides, spares were usually in stock.

While waiting, I became fascinated by onemechanic whose sole responsibility was to per-form lube, oil and filter (LOF) service…in thirtyminutes flat! This, coincidentally, was the samemechanic who, with a sandwich in one hand andborrowed tools in the other, asked me to park mymotorhome outside his LOF bay so the CV jointcould be replaced.With considerable mental reser-vation, I complied.The CV joint was installed, thesandwich consumed, a soda swallowed and thewheel jack removed all during lunch break!

Fortunate survivors of World War II came homeinstilled with a deep sense of discipline, cama-raderie and need for recognition.To fulfill thisneed, practically every fire department in thenation found an excuse for uniformed membersto engage in parade competition with other firecompanies. Musicians, not unlike Presidents, are

born egotists and are easily induced to providemelodious cadence for any parade. Instead of pol-ishing fire equipment for the next parade, music-men polish technique with a local band, which ismost often in dire need of replacement uniforms.Some method must be employed to raise funds.Well, how about selling pies?

Accordingly, the pie committee promptlyappointed the (only) member with a motorhome— and his muscular friend Pete — to “fetch”freshly-baked Shoofly pies from a bakery locatedwhere else…near Paradise, Pennsylvania. Each piewas sealed in a pie box.There were eight boxes in each two-cubic-foot shipping carton.Weightwas estimated at thirty-two pounds per carton.Atthis point a quick weight and balance computa-tion seemed to be in order.After all, we hadpromised to pick up two hundred and seventy-two Shoofly pies!

In true GMC Motorhome fashion, four cartonswere stashed under the bed, sixteen cartons on topof the bed, two under the (now converted)dinette, eight on top of the dinette bed, twostacked between the barrel chairs, and sixteenindividual pie boxes carefully nested on the (clean)floor of the shower.

There were a number of sobering and nostalgicmoments experienced on our return journey.First, the motorhome smelled like a bakery — forweeks! Second, the floor of the motorhome wasstartlingly close to the ground at the entrancedoor.Third, on the way to the “cockpit,” I wasreminded of numerous uphill treks to the “office”of a Douglas DC-3 aircraft. Forward vision wasnow well above the horizon, and the rear-viewmirror revealed approximately sixteen square feetof parking-lot asphalt.

There was a slight rise at the access of our busyhighway.At an opportune moment, we expeditedour entrance into traffic, and burned rubber forfifty yards before the front wheels finally settled to

Continued on Page 12

September 1995Number 5

INSIDE:WHAT’S NEW

• 3.42 POWER

COLORING

BOOK

SANDUSKY

SERVICE

COACH TALK

• SEWER ODOR

• THROTTLE KICKER

• OIL

CONSUMPTION

• QUICK COUPLER

• REFRIGERANT

CHOICE

R12, R134A,FRIGC, R406A

• TRANSFER SWITCH

TODD TS-30

• HITCH WEIGHT

• RUN ON

• OIL DILUTION

• SOOTY VENTS

TIME TO RENEW

CLASSIFIED

ADVERTISEMENTS

PUBLICATION

ORDER FORMS

PETE THE PIEPERSON by Walt Sener

A publication dedicated to the preservation of a classic and timeless vehicle

from the GMC Motorhome People

Motorhome

WHAT’S NEWThe 3.42 final drive began shipping in July almost20 years after Oldsmobile engineers designed itfor the GMC Motorhome.The original 3.07 finaldrive was the trailering final drive for the Olds-mobile Toronado passenger car, and it has alwaysbeen considered too high (too low numerically)and too vulnerable for the GMC Motorhome.The 3.42 final drive was designed for the motor-home’s tire size, frontal area and anticipated tow-ing loads. For these reasons, it is a broader-toothdesign than the original 3.07 final drive, whichhas a 14-tooth pinion and a 43-tooth ring gear.

The 3.42 final drive has a 12-tooth pinion anda 41-tooth ring gear. Its design makes the ring andpinion teeth as large as possible to withstandhigher motorhome loads.This is the only way tonumerically increase the ratio and the load carry-ing capability of the final drive, because its physi-cal size is fixed. If a GMC Motorhome final drivehad been designed from scratch, it would havebeen larger like the third member (differential) ina motorhome chassis of similar gross vehicleweight rating (gvwr).

The 3.42 ring and pinion gears are manufac-tured by Ohio-Richmond Gear, which is thelargest supplier of aftermarket, third-membergears in the world. Since General Motors nolonger cuts gears, it uses Ohio-Richmond Gearto manufacture all of the special gear sets for theGMC Motorsports program, and that’s why thecompany is making the 3.42 gears.

The 3.42 gear manufacturing was directed byJohn Bachelder who developed third-membergears for Oldsmobile when the 3.07 (E-car) finaldrives were made.The 3.42 final-drive assemblywas supervised by Art Haas who was the generalforeman of Oldsmobile’s third-member assemblyin the 1970s and 1980s. Both of these men areretired from Oldsmobile, and they joinedCinnabar Engineering, Inc. to oversee the 3.42final-drive program.Working under CinnabarEngineering’s license agreement with GeneralMotors, Duane McCormack found the originaldrawings and coordinated the program in hisretirement from Oldsmobile engineering.

The 3.42 final drive is sold only as an assembledunit, because very few shops have the E-car toolsthat are needed to properly assemble one. Fur-thermore, there are more than 60 shim variablesthat require substantial investment, and most

shops will not spend the money to get it right.The 3.42 final drive carries a 12-month, 12,000-mile limited warranty for normal applications.Here are reports from three regional users:

Increasing the GMC Motorhome engine speed to moreclosely approximate its originally designed engine

speed provides improved acceleration and hill-climbingability.This has been accomplished by changing the gearratio between the engine and the drive wheels, commonlyreferred to as the final-drive ratio. Originally, the gearratio was 3.07:1, which means the engine turns 3.07times faster than the driving wheels. Changing this ratio

Continued on Page 14

800-GMC-TRUCK (800-462-8782)for Recall assistance and general informationon GMC products.Monday through Friday 8:00 a.m. to 5:00 p.m. Eastern time.

800-720-CBAR (800-720-2227)for Genuine GMC Motorhome Parts andGMC Motorhome Operating and ServicePublications.Monday through Friday 8:00 a.m. to 5:00 p.m. Eastern time.

810-648-2444for GMC Motorhome Service.Monday through Friday 8:00 a.m. to 5:00 p.m. Eastern time.

810-648-9858for GMC Motorhome FAX and Voice Mail.Any day at any time.

gmcmh@aol.com for GMC Motorhome E-Mail.Any day at any time on the Internet.

231-258-4117for GMC Motorhome Technical Assistance.Monday through Friday 9:00 a.m. to 5:00 p.m. Eastern time.

GMC MOTORHOMETELEPHONE NUMBERS &

BUSINESS HOURS

GMC Motorhome Newsis published quarterlyby Cinnabar Engineer-ing, Inc., 116 OrvalStreet, Sandusky,Michigan 48471.TEL 810-648-2444FAX 810-648-9858gmcmh@aol.comCopyright 1995 byCinnabar Engineering,Inc.All rights reserved.Permission to reprintor quote excerptsgranted only uponwritten request andthen only when fullcredit is given source.Subscription priceUnited States, Canadaand Mexico: $10.00per year.All othercountries add $8.00per year. First Class orAir Mail postage paidat Sandusky, MI 48471and at other mailingoffices.

Wes CaughlanEditorial Director

Lisa YanagiharaArt Director

Lorraine GrahamAdvertising

Walt SenerContributor

Mad MacsGraphic Consultants

GMC Motorhome Newsdoes not knowinglyaccept deceptive ormisleading advertisingor editorial material.If you have a contraryexperience withrespect to anythingherein, please contactCinnabar Engineering,Inc. immediately.

The GM Emblem, theGMC Emblem andthe GMC MotorhomeParts Emblem aretrademarks of GeneralMotors Corporationand used under licenseto Cinnabar Engineer-ing, Inc.

Page 2

COLORING BOOK

The holidays are coming and CinnabarEngineering, Inc. has just the gift for thechildren in your family, both big andsmall. It is the GMC Motorhome Vacation-land Coloring Book. It was first printed anddistributed when the motorhome wasintroduced in 1973.

WhenCinnabarEngineeringagreed toput all GMCMotorhomepublicationsback into dis-tribution in1986, the color-ing book wasconsidered veryinteresting, butnot essential.TheOperating andMaintenance Man-uals had the highestpriority, the PartsBook came next, theService Bulletins andthe Recall Campaignscame after that, andthe MaintenanceSchedule completedthe list of essential service publications.

Once these publica-tions were completed,our Art Director, LisaYanagihara, couldn’t resistthe coloring book. It is awork of art.The line draw-ings wait to be filled in withthe colors of the rainbow,and they will warm the hearts of childrenof all ages.

The colorful book contains 16 pages of drawings featuring the GMC Motor-home.A mother bear and her cub beg forfood from the motorhome in GlacierNational Park. It appears at a Taos, NewMexico pueblo and at the Alamo in SanAntonio,Texas.The motorhome takes itsfamily to a marshmallow roast in the

shadow of the Golden Gate Bridge inSan Francisco, and on to Old Faithful inYellowstone National Park. Sun Valley,Idaho, Mount Rushmore, SequoiaNational Park, Baraboo,Wisconsin,Williamsburg,Virginia, Philadelphia,Pennsylvania,

Niagara Falls,and the Maine coast are other

destinations pictured. It concludes withdinner and bedtime in the GMCMotorhome.

The coloring book is available for$6.00 plus applicable tax and shippingcharges.An order form appears on page15 with the subscription renewal formfor GMC Motorhome News. Any numberof coloring books can be ordered. If youhave more than one child in your family,one will not be enough. �

Page 3

GMC Motorhome News … September 1995

SANDUSKY SERVICE

On September 1, 1995, Cinnabar Engi-neering, Inc. celebrated its secondanniversary of consolidated operation inSandusky, Michigan. During that two-year period, a lot has happened. Employ-ment has increased to 18; thirteen workin Sandusky and 5 work elsewhere. Morethan 900 new GMC Motorhome PartNumbers and countless used GMCMotorhome Part Numbers are in aninventory that totals morethan 200,000 parts.A 5-workstation computersystem has been installedto keep track of more than7000 GMC Motorhomeowners and 6900 GMCMotorhome part numberslisted in the 78Z Parts Book.Three 25,000-pound liftswith 12,000-pound rollingjacks have been installed alongwith a 6-wheel alignment station and engine diagnosticequipment.The cabinet shop hasbeen enlarged, and the body andpaint shop has been upgraded tomodern clean-air and industrialsafety standards.

All of this has been done to bet-ter serve GMC Motorhome ownersworldwide under our license agree-ment with General Motors Corpora-tion.The winter months are often thetime to get major mechanical, interiorand exterior work performed. ServiceManager, Ivan Henderson, welcomescustomers from all over North America.They bring their GMC Motorhomes toSandusky during the off season, and wedrive their owners to the Detroit Metro-politan International Airport.When thework on the motorhomes is completed,we store them inside and pick up theirowners at the airport when they canconveniently return. Owners from theeast and west consider the trips to San-dusky a vacation, because they only haveto drive one way each time, and they canoften travel a different route coming andgoing. Check with your travel agent.

Roundtrip airline tickets with distantdeparture dates are very reasonable andperiodically on sale.

During the past two years the exteriorgroup has developed a number of newpaint designs that adapt to many differentcolor schemes.The interior group workswith these colors to come up with com-plementary furnishings that usuallyinclude matching leathers, hard-woods, headliners

and valancedday/night blinds, which are only

found elsewhere in high-line motor-homes. New appliances, air conditioners,water heaters, furnaces and the mostsophisticated gadgets abound.The lateststereo and CD players are available as arethe new small digital satellite dishes thatcan be roof mounted along with anten-nas for a cellular telephone and the usualCB and AM/FM radios. For those inter-ested in shopping at home before comingto Sandusky, photo portfolios can be sent.

The mechanical shop is now staffedwith four certified mechanics, headed byEric Priemer who is a certified mastermechanic.A GMC Motorhome doesn’talways have to come to Sandusky to getour expert mechanical attention. Increas-ing numbers of GMC Motorhome own-ers are having their local mechanicsremove their front hubs every 25,000

miles and ship them to Sanduskywhere the mechanical shop has thespecial tools to remove the front-wheel bearings and replace themwith the heavy-duty and properly-spaced GMC Motorhome bear-ings, which are part number12351677. Longer GMC Motor-home wheel studs for Alcoa alu-minum wheels can be installedat the same time.

Other GMC Motorhomeowners are strapping their reartandem-axle assemblies to apallet and shipping them toSandusky to have themstraightened and have thepins and bushings replaced.When they are returned, allthe local mechanic has todo is reinstall them andshim them for propercamber and toe align-ment in accordance withinstructions and specifi-cations in MaintenanceManual X-7525.

We also have a spe-cial truck and trailer

combination that wasbuilt to retrieve a wrecked or disabledGMC Motorhome.We can send it to getyour motorhome, but the various emer-gency road services will generally costless. However, many of them will not bewilling to deliver your GMC Motor-home to Sandusky.

Everyone at Cinnabar Engineering,Inc. is proud of our Sandusky, Michiganfacility.We hope you will come and visitand bring your GMC Motorhome. Ifyou can’t bring your motorhome, justgive us a call.We’ll pick you up at the airport or at the side of the road. �

Page 4

CC

Sewer OdorWhile we were visiting in Wisconsin this sum-mer the outdoor temperature soared to 113degrees F. I had a new holding tank installedin my 1977 Kingsley earlier this year, and weexperienced considerable sewer odor in themotorhome when driving in hot weather.

We did everything possible to keep the inte-rior of the coach cool, including driving withthe driver- and passenger-side windows open.Even though we used holding-tank chemicals,we could not get rid of the sewer odor. It wasparticularly noticeable in the galley area.

Do you think my new holding tank is leak-ing sewer gas into the motorhome? Can yousuggest a holding-tank chemical that will atleast mask this odor?

Frank WaltonRochester, Minnesota

Idoubt if your new holding tank isleaking sewer gas, Frank.The three

roof-top vents on your 1977 Kingsley do a more than adequate job of ventingthe holding tank.

Hot weather causes more sewer gas tobe generated, and driving with the dri-ver- and passenger-side windows opencreates a partial vacuum in the motor-home.This in turn causes sewer gas toflow down the refrigerator vent andmake the coach stink inside, particularlyin the galley area.

The primary cure is to keep all sidewindows closed, and the HVAC bloweron high.This will keep sewer gas androad dust out by partially pressurizing theinside of the motorhome. I experiencedthe same problem with my new 1976Glenbrook in the summer of 1976.A callto GMC Motorhome Technical Assis-tance got me this answer, and it solvedthe problem.

As far as holding-tank chemicals areconcerned, only formaldehyde-basedchemicals will mask holding-tank odor.The supposedly more environmentallysensitive enzyme chemicals mute hold-ing-tank odors by digesting the waste,

but they can’t keep up with it in hotweather and they don’t work at all incold weather because the bugs go tosleep! Thetford’s original Aqua-Kemchemical seems to do the best job mask-ing holding-tank odor, and I have triedjust about everything in the market.

Liquid Aqua-Kem can be messy, and itwill often stain white plastic parts that arecommonly found in GMC Motorhomebathrooms. Granular Dri-Kem is a bitmore expensive, but it is a lot easier touse and does not make a mess. Simplyopen the packet, step on the toilet-flushpedal and dump the granules into theopen hole. One packet will keep a GMCMotorhome holding tank smelling pleas-ant in all but the hottest weather.Whenthe weather is really hot, two packets pertank will generally do the job.

Throttle KickerThe second paragraph on page 6T-8 of Maintenance Manual Supplement X-7725describes the action of the Throttle Lever Actuator (TLA).The TLA prevents 403-cidengines from going to idle in the decelerationmode.This reduces brake life and makes themotorhome more difficult to stop.

Many years ago I disconnected the TLA onmy 1978 Palm Beach. Handling improvedwhen decelerating, particularly when shiftingdown. I think every GMC Motorhomeequipped with a 403-cid engine should havethe TLA disconnected.A small ball bearinginserted in the vacuum line will do the job.

Roy ReitterManchester, Missouri

The TLA on the motorhome has apassenger-car origin, Roy. Both the

455- and 403-cid engines were certifiedFederally and in California as passenger-car engines.As a result, the GMCMotorhome has the same emission-con-trol devices as the Oldsmobile Toronadowith the exception of an EGR valve.

The TLA makes braking more diffi-cult, and it reduces downhill decelera-

tion. Earlier GMC Motorhomes did nothave a “throttle kicker,” and I can under-stand why you disconnected it on yourmotorhome.

Other 1977 and 1978 GMC Motor-home owners with 403-cid engines maywant to disconnect their throttle kicker.If the motorhome is registered in a statethat periodically inspects emission con-trols, those who disable the TLA shouldmake sure that the ball bearing or otherplug is removed before the next smoginspection.

Oil ConsumptionMy 1976 Birchaven hasn’t been used a lotsince I purchased it in 1988 with 50,000miles on the odometer. It now has only70,000 miles on it.The 455-cid enginealways starts easily, and it runs great.

However, I have been getting only about500 miles per quart of oil during relativelyeasy flat-land driving.The engine does notseem to be burning oil because there is no bluesmoke.There seems to be some oil-pan wetnessaround the pan gasket, which appears to befactory original.

A mechanic suggested that I replace the pangasket, and consider renewing the valve-stemseals. Both of these are onerous tasks which Iam reluctant to undertake if there are otherthings I ought to check out first. I wouldappreciate your comments on 455-cid engineoil consumption that I may be overlooking.

Al Schwarzvia the Internet

Your oil consumption is a bit on thehigh side,Al, but it is not unusual.

When my GMC Motorhome was brandnew, it used a quart of oil every 800 to900 miles. Now, it is using a quart of oilevery 600 to 700 miles with 78,000 mileson the odometer.

Engine-oil mileage goes down as vehi-cle weight goes up.There is a chart in theChevrolet Motorhome Chassis Service Guidethat shows acceptable oil consumption asa function of gas mileage, which also

Page 5

Coach Talkby Wes Caughlan

GMC Motorhome News … September 1995

goes down as vehicle weight goes up.The minimum acceptable oil con-

sumption for an engine getting 7.5 milesper gallon of gasoline is 500 miles perquart of oil. Marginal oil consumptiongoes down to 250 miles per quart of oilat 7.5 miles per gallon of gasoline. How-ever, marginal oil consumption is usuallycaused by external leaks, a malfunction-ing PCV system or missing, worn or mis-located valve-stem seals.

At 70,000 miles, your oil consumptionis a bit on the high side, but I would notworry about it too much.Your valve-stem seals are worn, but probably notenough to justify a valve job. If possible,fix or slow down any leaks and keep aneye on your consumption. If it staysaround 500 miles per quart, and theengine runs as well as you say, don’tworry about it. I would rather have anengine that uses a bit too much oil thanone that doesn’t use any oil at all.

Quick CouplerI recently acquired a 1977 Royale, and hadproblems with the air suspension.After readingcopies of your preventive maintenance articlesthat were published in 1980, I upgraded myElectro Level I air-suspension control system.The air suspension now works better than Ihad imagined, and campsite leveling is a joy.

If the air-suspension control system canpump up two air bags and keep them properlyinflated, why can’t it pump up a tire or otherinflatable things like a basket ball? Also, Ihave a large compressor in my work shop.Why can’t I turn off the little, twin-cylindercompressor and use my shop air when themotorhome is parked near my shop?

Warren BaldwinNashville,Tennessee

You can do both,Warren. Let’s takethem one at a time.The twin cylin-

der compressor will pump up a tire ifyou let it do so in stages. Pumping up aGMC Motorhome tire to 75 psi is likepumping up a whole bunch of air bags. Itwill easily top off all of your tires withouta rest, but it should be allowed to rest andcool once or twice when pumping up an

entire tire. Keeping the motorhomeengine running or boosting the batteryto allow the converter to keep the volt-age up at the compressor will expeditethe process.

If you go back to the 1980 articles, youwill notice there is a brass quick couplerattached to the air tank in the pictures.This is the way you get the air out of1973 through early 1976 Power Levelair-suspension control systems. Simplyplug in an air hose with an attached infla-tor, start the motorhome engine or boostthe engine battery to keep the voltageup, and go for it!

Getting the air out of an Electro LevelI air-suspension control system is almost

as simple.A 1⁄4-inch, female-pipe openingmust be created to install the quick cou-pler. Replacing the 1⁄4-inch street elbowthat connects the air tank to the ElectroLevel I manifold with a 1⁄4-inch male-branch tee is the easiest, and it makes thequick coupler readily accessible.

Alternatively, you can attach a clip-onair chuck to the Schrader valve at thebottom of the air tank, but it often sup-plies rusty water and debris along withthe air.As a result, the Schrader valveshould only be used as a drain and thensealed with a pressure-sealing valve cap.

Once the quick coupler is installed, theElectro Level I procedure is the same asthe Power Level procedure with a couple

of exceptions.Turnthe ignition on or tothe accessory posi-tion. In addition tostarting the motor-home engine orboosting the enginebattery to keep thevoltage up, themotorhome shouldbe at normal rideheight and the cen-ter control switchshould be put in theTravel Auto posi-tion.The compres-sor will only operatein this position andnot change normalride height. If themotorhome is not atnormal ride height,the system willadjust the air sus-pension to normalride height at thesame time it is beingused as an inflator.

Using an ElectroLevel II system tosupply air is not aseasy, because there isno air-storage tankand the little com-pressors do notpump a lot of air.

Page 6

An upgraded Electro Level I module with a quick coupler,copper air-cooling loop, stainless-steel check valve, 5-micronfilter, pressure-relief valve, pressure gauge and brass air-brakefittings.A dual-foot inflator is attached to a 25-foot air hose.

One of the compressors can be used tosupply air by attaching a clip-on chuck tothe Schrader valve in its head, turning theignition on or to the accessory position,starting the motorhome engine or boost-ing the engine battery to keep the volt-age up, and switching the center controlswitch to the Travel Auto position whenthe motorhome is at normal ride height.Initially, air will come from the air bagthat the compressor normally supplies.When the height control sensor detects alowering ride height on that side, the

compressor will start and attempt to pickup the inflation chore.

By creating a double-nipple adapterfrom a 1⁄4-inch male and a 1⁄4-inch femalenipple, air can be added to Power Leveland Electro Level I air-suspension con-trol systems from an external source, suchas your shop compressor. Since PowerLevel systems do not require the ignitionswitch to be turned on or to the accesso-ry position to operate the valves, simplyplug the shop air into the air tank and setthe dashboard controls.

Electro Level I systems can be operatedsimilarly with two exceptions.The igni-tion switch must be turned on or to theaccessory position, and the twin-cylindercompressor must be turned off.Turningthe compressor off can be as simple asunplugging its red lead from the wiringharness. However, that may be easier saidthan done, because the connection maynot be readily accessible.The easiest wayto turn an Electro Level I compressor offwhile using shop air is to install a pressureswitch that has a manual switching lever.Furnas makes such a switch, and it isavailable from Grainger outlets through-out the U. S. It is Grainger no. 4A088,which is Furnas part no. 69MB7L.

Adding air to an Electro Level II sys-tem is also quite simple.A clip-on chuckat the end of a shop-air hose is attachedto the Schrader valve on one or the otherElectro Level II compressors. Like ElectroLevel I, the ignition switch must beturned on or to the accessory position,and the compressor must be turned off.The best way to turn an Electro Level IIcompressor off is to unplug it.

Refrigerant ChoiceAccording to my local mechanic, Freon (R12)can no longer be manufactured after the end ofthis year. It is the refrigerant that was used inall GMC Motorhome dashboard air-condi-tioning systems.

Every spring, I have to top off my air con-ditioning system when I prepare my 1976Eleganza II for the season. Up until a year orso ago, I purchased little 12-ounce containersof Freon and did it myself. Now, I have to go

to a certified facility to get it done. In addition,the Freon has become very expensive.

What will I do next year to top off my system? Is there a replacement gas? Or, will I have to install a new dashboard air-condi-tioning system?

Jerry SandersOmaha, Nebraska

For the next couple of years, Jerry, youwill be able to continue as in the past.

While Freon (R12) cannot be manufac-tured after the first of the year, most ser-vice-oriented companies have beenstockpiling it. General Motors has advisedCinnabar Engineering, Inc. that it will beable to supply R12 for at least 2 moreyears. However, it must be installed by acertified facility that has recovery equip-ment, and the gas itself has become rela-tively expensive.

A new refrigerant called R134A hasbeen installed in new vehicles for the pastfew years. Initially it was not as efficientas R12, but component redesign has justabout eliminated performance differ-ences. Unfortunately, R134A is not com-patible with the mineral oil used in anR12 system, and the entire system shouldbe replaced to avoid contamination andprovide proper containment.

Replacing the entire GMC Motor-home dashboard air-conditioning systemis not as bad as it may sound, because allof the systems are getting up in years.Air-conditioning compressor and othercomponent replacement is common, andchanging to an R134A system at thattime should save money in the long run.

Alternatively, new gases are cominginto the market that are compatible withthe R12 mineral oil, but all of these gasesrequire new connection fittings and con-tainment hoses.They cannot be used totop off an R12 system like you have beendoing in the past, but they can be used toreplace R12, which can be removed fromthe system.

The first new gas approved by theEnvironmental Protection Agency (EPA)is called Frigc. It was recently covered byU. S. Patent 5,425,890, and it is manufac-tured by Intermagnetics General of Lath-

Page 7

GMC Motorhome News … September 1995

A clip-on chuck can be used to access anElectro Level II system.

Male and female couplers and nipplesmake connections easy.Air can be addedwith a double-nipple adapter.

am, New York.Another new gas isR406a, which is covered by U. S. Patents5,151,207 and 5,214,929.According toits manufacturer, Monroe Air Tech Incor-porated of Bloomington, Indiana, R406ais more efficient than R12, and it will beavailable for automotive air conditioningsystems in early 1996.

At the moment, Frigc is considerablymore expensive than R12 or R134a.However, now that the patent has issued,the manufacturer says large-scale manu-facturing should bring the price down.Even if the cost is higher, Frigc or R406amay be the most economical alternativesonce R12 supplies are exhausted. Frigc iscurrently selling for around $25.00 apound, and a GMC Motorhome takes 3to 4 pounds.The material cost to changea GMC Motorhome dashboard air-con-ditioning system from R12 to Frigcshould not exceed $100.00. Consideringthat R134a retrofit parts will cost morethan those for Frigc or R406a, thesealternative gases may become one of thebetter bargains in the market.

For the time being, I would just sit andwatch.The retrofit market has not devel-oped because R12 is still available.As itsavailability declines, more alternativesmay appear.

Transfer SwitchI have a 1978 Royale that has 2 roof air con-ditioners and a microwave oven.The 120-voltAC shore-power cord is rated at 30 amps.When I am hooked up in a campground, Ican run the front air conditioner and themicrowave. If I want to run the rear air condi-tioner, I have to start the Onan generator.

When I leave the campground, I can onlyrun the rear air conditioner when I start thegenerator. No other 120-volt AC circuit isactive unless I fold up the bed, remove anupholstered panel, and turn the shore-powerbreaker off and the generator breaker on.Thereis a flipper on one of these breakers that won’tlet me turn them both on at the same time. Isuspect that is to prevent one circuit from feed-ing back into the other.

I have thought about having an electricianmove the circuit-breaker panel to a more acces-

sible location, but that wouldn’t be cheap.Recently, a friend came to visit in a 1994Holiday Rambler motorhome that had a simi-lar 30-amp shore-power cord. Even though hismotorhome was plugged into only a 15-ampoutlet at my home with an adapter, he couldrun both air conditioners and all other 120-volt AC appliances by simply starting his 6.5kw auxiliary generator.When he unplugged,the same was true and he didn’t have tochange any of the circuit-breaker switches.

How does a 1994 Holiday Ramblermotorhome completely switch to generatorpower automatically? How can I make my1978 Royale do likewise?

Ken ParksTulsa, Oklahoma

Holiday Rambler does it with atransfer switch, Ken. In fact, almost

all new motorhomes use transfer switchesthat are made automatic with solid-stateelectronics that did not exist in 1978.

There are several automatic transferswitches in the market.Todd Engineer-ing’s TS-30 can eliminate the two break-

ers in your Royale, and you will not haveto fold up the bed to have 120-volt ACpower whenever you want it.

Most Royales with two air condition-ers have two circuit-breaker panels.TheOnan generator supplies one panel thathas a 20-amp breaker for the rear air con-ditioner and a 40-amp breaker that sup-plies a neutral-switching, 30-amp mainbreaker in the second panel.A secondneutral-switching, 30-amp main breakerin the second panel is supplied by theshore-power cord.The flipper on one ofthese breakers prevents them from beingturned on simultaneously.

The second panel has 15- and 20-ampbranch breakers.They supply the front airconditioner, the microwave oven and the120-volt AC receptacles.This panel isbasically a 30-amp panel, and it needsonly one 30-amp main breaker.A trans-fer switch can supply the main breakerwith either generator or shore power,eliminating the need for the second mainbreaker and the flipper.

A Todd TS-30 transfer switch costsabout $75.00, and it is easy to install.Simply choose one 30-amp breaker asthe main breaker and abandon the other.Remove the generator wires from one30-amp breaker and attach them to thegenerator input terminals on the transferswitch. Remove the shore-power wiresfrom the other 30-amp breaker andattach them to the shore-power input

Page 8

A Royale 30-amp, 120-volt AC panelwith two main breakers and a flipper.Thebreaker with the flipper can be eliminatedwith an automatic transfer switch.

The Todd TS-30 has a 20- to 30-secondtime delay to let the generator warm up.

terminals on the transfer switch. Beforemaking these connections, make sure theneutral wires are attached to the neutralterminals and the hot wires to the hotterminals.Then, run a pair of 10 AWGwires from the output of the transferswitch to the chosen 30-amp mainbreaker. Finally, ground the transferswitch by attaching a length of chassis-grounded 8 AWG copper wire to theground bar in the box.

The generator will now supply the rearair conditioner and the transfer switch.The shore-power cord will supply thetransfer switch which defaults to shorepower. It will automatically switch togenerator power after a 20- to 30-secondtime delay when the solid-state electron-ics detect 120 volts AC at the generatorterminals.The time delay allows the gen-erator time to warm up.

After installing the transfer switch, plugthe shore-power cord into a 30-amp,120-volt AC receptacle.With the excep-tion of the rear air conditioner, all 120-volt AC circuits should be active. Unplugthe shore-power cord and start the Onan

generator.After a 20- to 30-second timedelay all 120-volt AC circuits should beactive, including the rear air conditioner.

Shut down the Onan and the transferswitch will turn off all AC power. Plugthe shore-power cord back into the 120-volt AC receptacle, and AC power will berestored to everything but the rear airconditioner. Now, start the Onan with-out unplugging the shore-power cord.Again, after a 20- to 30-second timedelay all 120-volt AC circuits should beactive, including the rear air conditioner.Even though the shore-power cord is stillplugged in, all 120-volt AC power willbe coming from the generator.When thetransfer switch switches from shorepower to generator power there will be amomentary power interruption.Thattells you there will be no feedback ineither direction.

One word of caution. Even though atime-delay transfer switch is controlling120-volt AC power, do not start or stopthe Onan generator with any 120-voltAC appliance turned on. Make sure thatall AC appliances are turned off beforestarting or stopping the generator to pre-vent variable voltage problems.

Hitch WeightI recently bought a 1976 Royale, and just hada set of 8.75R16.5 LRE Michelin XPS tiresinstalled on it. I also own a Harley-Davidsonmotorcycle. Can I hang a 400-pound Harleyon the back of my GMC Motorhome withoutcompromising anything?

Irving “RJ” MaceWare, Massachusetts

You can hang anything you want onthe back of your GMC Motor-

home, RJ, but your new Michelin reartires and you won’t like a 400-poundmotorcycle back there.Why? The answeris quite simple.

The rear bumper is almost 9 feetbehind the center of the tandem axle, andthe center of a motorcycle rack would beabout 10 feet back.A 400-pound motor-cycle would put more than a 4000 foot-pound lever on the rear axle.This in turn

would transfer weight from the front tothe rear and partially unload your frontaxle, which is already too light to main-tain really good traction.The end resultwould be overloaded rear tires andwheels, and lousy steering and stability.

The Chevrolet Motorhome Chassis ServiceGuide gives the formulas for calculatingthe weight transfer. Let’s take a look.

Your 1976 Royale has a 160-inchwheelbase, and your 400-pound motor-cycle will be about 120 inches behindthe center of the rear axle. Since 120 is75 percent of 160, your rear axle weightwill increase by 400 pounds plus 75 per-cent of 400 pounds (300 pounds), whichtotals 700 pounds! Your front axle loadwill decrease by 300 pounds, which willsimply exacerbate the GMC Motor-home’s inherent front-traction problem. Icall this the teeter-totter effect.

We have long said that hitch weight ona GMC Motorhome should not exceed100 pounds. If it does, a load-equalizinghitch is necessary to maintain stability. Inaddition, any added weight should bebraked, and that has become quite anissue in the motorhome industry today. Ifyou put your motorcycle on a trailer, thetrailer can have brakes.A braked trailerwill probably have less than 100 poundsof hitch weight, and you and your Harleywill be happy campers!

Run OnI had the carburetor remanufactured on my1976 Palm Beach early this summer.Aftergetting it back, I started experiencing run onwhen I shut the 455-cid engine down withthe transmission in Park.

The motorhome has 106,000 miles on it,but otherwise it runs great.What is causing therun on and what can be done to stop it?

John SchwietertRapid City, South Dakota

Anumber of things cause run on,John. Since the ignition is off, some-

thing has to cause ignition. In an olderengine it is usually hot carbon deposits inthe engine, and your engine qualifies inthat regard.

Page 9

GMC Motorhome News … September 1995

The transfer switch switches both the hotand the neutral circuits.The pigtails arefor the generator connection.

Page 10

Vaporized fuel and air also must bepresent to sustain run on.Today’s refor-mulated gasolines, which vary in volatili-ty, and hot summer weather are often allit takes to keep some vaporized fuelflowing into the engine after shut down.When the transmission is in Park, verylittle fuel is required to sustain run on. If

the engine is shut down when the trans-mission is in Drive or Reverse, the loadwill usually prevent run on under thesecircumstances.

When your carburetor was remanufac-tured, the idle-mixture and slow-idleadjustments were arbitrarily set. Finaladjustments cannot be made until the

carburetor is installed on the engine.Theadjustment procedures are described inmaintenance manual X-7525. If the finaladjustments have not been made, the car-buretor may be contributing to the prob-lem with an overly rich idle mixture oran improper throttle-valve position.

Oil DilutionThank God for the return of intelligent com-mentary on GMC Motorhome problems! Ihave incurred a problem and need your help.

On my last trip I noticed that my crankcasehad about 4 quarts more oil in it when Ireturned than when I left town. I immediatelyassumed that the fuel pump was leaking andreplaced it. On a try-out run of several miles,I again found that my oil was contaminatedwith gasoline.

What is causing this dilution? How can itbe stopped?

Milton KielsmeierForestville, California

Your carburetor is dumping gasolineinto your engine, Milt.This can se-

riously damage the engine because itwashes down cylinder-wall lubrication.

If your fuel delivery system is workingproperly and has not been modified withan auxiliary electric fuel pump, the causeis the float valve in the carburetor. It issimilar to the float valve in a toilet. Eitherthe float is saturated with gasoline andnot rising in the bowl, or the valve issticking open. Both conditions are easy tofix during a minor carburetor overhaul.

However, check the fuel pressure at theOEM fuel pump first. It should notexceed 5 psi at the inlet when the engineis idling. If it does, excessive pressure maybe forcing the float valve open, causingthe carburetor bowl to become overfilled.This will allow gasoline to overflow intothe engine.

Excessive fuel-pump-inlet pressure canbe caused by unregulated, auxiliary elec-tric fuel pumps that are pressure additive,such as an AC EP12S or an AC EP89.Aplugged liquid/vapor separator or carboncanister also can cause excessive fuel-pump inlet pressure, particularly when a

Page 11

bad gas cap does not relieve fuel-tankpressure between 2 and 3 psi in accor-dance with specifications.

Sooty VentsRecently, both the water heater and the furnacevents have been turning a deep black on my1977 Royale. I cleaned both burners and hadthe regulator tested by a gas company.Thetechnician told me that the pressure was toolow, so I purchased a new regulator and hadthe pressure set.

I blew out all of the burners with compressedair and still have the problem.There are alsostrong fumes from the stove burners. Please tellme what I can do to eliminate this problem.

George McManusPeoria, Illinois

Normally, sooty deposits on exhaustvents indicate too much LP-gas

pressure, George.They also can indicateinsufficient combustion air, and I suspect

that is your problem assuming your newregulator is delivering 10.5 to 11 incheswater-column pressure to the affectedappliances.

Strong fumes from the stove burnersare a clue, because that indicates a build-up of odor agent in your propane tank.The odor agent is a “perfume” that ismixed with propane to give it a smell,and it is slightly heavier than propane.Over the years perfume builds up in thebottom of any propane tank, and it cancreate quite a stink in a motorhome, par-ticularly when the tank is close to beingempty.To get rid of the smell, have aknowledgeable LP-gas service facilitydrain the tank and then pressure purgethe tank with propane vapor to eliminateintroduced air.

More importantly, this perfume attractsinsects. Mud dauber insects are the mostcommon.These pesky rascals crawl intocombustion-air vents and build nests thatsubstantially reduce combustion-air flow.

For some reason they rarely block a com-bustion-air passage completely so theappliance works, but it soots badly.

The combustion-air tube on mostwater heaters is relatively easy to cleanwith a bottle brush and other small toolsthat are usually necessary to break theinsect nests loose. Cleaning the combus-tion-air passages in a furnace is anothermatter.The furnace usually has to beremoved from the motorhome and dis-assembled.This work is generally bestperformed by a service center for theparticular furnace.

Wes Caughlan is President of Cinnabar Engi-neering, Inc. Cinnabar Engineering, Inc. isGeneral Motors’ licensee for the distribution ofall GMC Motorhome Parts and Publications.Address correspondence to 10836 West LoyolaDrive, Los Altos Hills, California 94024;E-Mail Cbar@eworld.com on the Internet;FAX 415-948-6263.Telephone 415-948-8664 Monday through Friday 8:30 a.m.-5:30 p.m. Pacific Time. �

GMC Motorhome News … September 1995

Page 12

Continued from Page 1the road surface.What amazing power!The ol’ Glenbrook felt like a big boat outof water.

One sneaky way to encourage audi-ence attendance at summer-in-the-parkevents is to wait until after the band con-cert to distribute 1088 pounds of mouth-watering Shoofly pies.With each cartonremoved from the motorhome, therewould be a disconcerting hiss of air fromthe height-control valves.The ladies werenot impressed with the strange hissingsound. Someone even suggested that itsounded like a mechanical sigh of relief.Ol’ Glenbrook even hissed at ourmailperson when she bounced by with a blond pony tail and really short, shortshorts.That hiss to me seemed to bemore a hiss of delight than anything else.

Pete, now known as the pieperson,

remarked how high the rear of themotorhome seemed to ride, minus allthose pies.To me, it seemed once again to be the inimitable GMC Motorhome.

On the way home, by a majority vote,we were coerced into a circuitous detourby way of the local ice-cream emporium.Six 10.7-ounce sections of Shoofly piewere smothered with ice cream andserved. Pete insisted this action was essen-tial to stabilize our motorhome’s centerof gravity by four pie pounds. Under thecircumstances, who in the world couldturn down Shoofly pie a la mode servedby Pete The Pieperson.

Walt Sener has played the trumpet since1929, had a newspaper route and was a gym-nast of note. He retired after 37 years with theDepartment of Defense and has been writinganecdotes about the GMC Motorhome sincethe 1970s. �

TIME TO RENEW

For most subscribers, September 1995 isthe month to renew their subscription toGMC Motorhome News.Your renewalmonth and year follow your name on theenvelope that brought you this issue.

The subscription price is still only$10.00 per year for First Class Mail sub-scriptions sent to addresses in the UnitedStates, Canada and Mexico. Subscribersin other countries should add $8.00 peryear to cover Airmail charges.

A subscription renewal form appearson page 15. It can be used or copied andreturned with your check made out toCinnabar Engineering, Inc.To save theannual nuisance and paperwork, considerrenewing for two or more years andguard against any future increase in theprice of a subscription. �

Call us with your

requirements.

Winterfeldt

At Winterfeldt . . . We Build Custom and Standard Engines for GMC Motorhomes.We Can Bring Them To You.

5468 GUNBARREL ROAD, LONGMONT, COLORADO 80503 • PHONE (303) 530-4995

Motorhomes For Sale1978 Royale 26-foot,Rear Bath.47,000 Original Miles. Original Owner.Tub/Shower, Generator, Roof Air, Pod,TV, Microwave. Sleeps 6.Whistle Clean.Smooth Riding Classic. $20,000. FrankTowle, Scottsdale,AZ; 602-860-6996.

1978 Eleganza II 26-foot, Side Bath.Full Cabinets, Microwave Oven, 6kwOnan,TV Antenna, Roof Storage Pod,Awnings, Central Vacuum, CB Radio.Non Smokers. $27,500. Bruce Smallman,Phoenix,AZ; 602-973-1035.

1977 Eleganza II 26-foot, Side Bath.New Engine with Warranty. CompletelyRedone Inside and Outside. New AC,Furnace,Water Heater,Transmission,Tires, Bearings, Brakes, Bilsteins. $30,000.Paul Kane, Mesa,AZ; 602-924-7370.

1977 Royale 26-foot,Twin Beds.56,000 Original Miles. Dry Bath, 455-cidEngine. New Interior, Refrigerator, MiniBlinds,Valances. $23,500. Doug Laubhan,Woodward, OK; 405-256-7177.

1977 Kingsley 26-foot, Side Bath.85,000 Original Miles. Clean Inside.New Radiator,Tires, Furnace. Spare AirBag and Maintenance Manuals. Non-Smokers. $22,000. John Mathison,Brookings, OR; 503-469-6930.

1977 Birchaven 23-foot, Side Bath.61,000 Original Miles. 455-cid Engine.$10,000 in Renovations. Pleated Blinds,Berber Carpet, Michelins, Bilsteins. NewWindshields. Stored Inside. Lynn Street,Young America, MN; 612-467-3375.

1977 Royale 26-foot, Dry Bath.Two Roof Air Conditioners, 403-cidEngine.Three-Speed Roof Vent, 6 kwOnan, Storage Pod, Parts Book andMaintenance Manuals. Real Nice Coach.$22,500. Robert Duncan, Roodhouse,IL; 217-587-2861 After 6:00 P. M.

1977 Royale 26-foot,Rear Bath.73,500 Original Miles. Upgraded AirSuspension, 455-cid Engine. New FrontShocks, Hoses,AC Condenser,Air Bags.Need Larger Coach.Trade for 1988+ 28-to 31-Foot RQB Coach, or $19,500.James Lingle, Cobden, IL; 618-893-2829.

1976 Glenbrook 26-foot, Side Bath.65,000 Original Miles. New Carpet andDrapes. Stored Inside. Excellent Condi-tion. $26,000. Paul Heltzel, Niles, OH;216-544-4025.

1976 Birchaven 23-foot, Rear Bath.34,000 Original Miles, Sleeps 4. New 10-Ply Rated Radial Tires. Original Paint,Well Maintained. $5000 in Updating,Including a Screen Door.A Super CoachReady to Travel. $26,000. R. E. Monk,Monticello, IA; 319-465-3346.

1976 Eleganza II 26-foot, Side Bath.56,000 Original Miles. Nevada Coach.New Carpet, Full Size Rear Bed, BarrelChairs, Couch,Venetian Blinds. NewEngine,Transmission,Tires, Shocks, 3-inch SS Exhaust. $22,500 OBO.WillTrade Up, Down or Sideways. KeithRush, Las Vegas, NV; 702-361-5322.

1976 Glenbrook 26-foot, Side Bath.52,000 Original Miles. Stored Inside andWell Maintained. Excellent Condition.$25,000. Ruby Crispell, Norwich, NY;607-334-8533.

1976 Birchaven 23-foot, Side Bath.Rebuilt Engine and Transmission. Cus-tom Window Decoration. Many NewParts. Records and Receipts. $15,000.Ron Porter, Redford, MI; 313-534-8147.

1976 Eleganza II 26-foot, Side Bath.84,000 Original Miles. Custom LeatherInterior. New Refrigerator, Headliner,Carpet, Drapes. Corian Counter Tops.Two Roof AC. Excellent Mechanicalwith Updates. See To Believe. $24,500.R. B. King, Florence, SC; 800-467-5464.

1976 Birchaven 23-foot, Rear Bath.78,000 Original Miles. New Paint andInterior. Microwave, 4 kw Generator, CBRadio, Stereo, Roof Pod. $22,500. DickMcGuire,Amarillo,TX; 806-355-8757.

1975 Eleganza II 26-foot, Side Bath.Nearly New Tires, Carpet,Two-WayDometic Refrigerator, Bilstein Shocks.Stored Inside. $17,000.Wayne Cramer,Bondurant,WY; 307-733-5618.

1974 26-foot, Side Bath.455-cid Engine, 6.5 kw Generator,TwoRoof AC. Extra Engine,Transmission andFinal Drive. $18,500. Jerry Hudson,Jasper,AL; 205-384-4612.

1973 Custom 26-foot, Side Bath.90,000 Original Miles. Fuel Injected HEI455-cid Engine. Gaggenau Stove, CorianCounter Tops,Awnings, Chrome Wheels,New Tires, Screen Door. Loaded WithMuch More. $23,000 OBO. GeneTrester, Los Angeles, CA; 213-291-0508.

1973 Canyon Lands 26-foot.53,000 Original Miles. CompletelyRebuilt. Many Custom Items. Built-InCouch, New Air Suspension,WallaceHubs, Bilstein Shocks. New Appliances.$20, 000 OBO. Ed Harris, Columbus,GA; 706-568-6759.

AdvertisingSubscribers are entitled to one non-commercial classified advertisement per year at no charge.Additional non-commercial advertisements in the sameyear are $1000 each. Commercial Advertising Rates are available onrequest.Advertising should be directedto: Lorraine Graham, Cinnabar Engineer-ing, Inc., 116 Orval Street, Sandusky,Michigan 48471,TEL 810-648-2445,FAX 810-648-9858.

The closing date for the December 1995 issueis November 10, 1995. �

GMC Motorhome News … September 1995

CCCC llll aaaa ssss ssss iiii ffff iiii eeee dddd AAAA dddd vvvv eeee rrrr tttt iiii ssss eeee mmmm eeee nnnn tttt ssss

Page 13

Continued from Page 2to 3.42:1 increases the engine speed to approximatelythe same revolutions per minute (rpm) it turns in anOldsmobile Toronado at the same highway speed. In my 1978 Palm Beach with an original 403-cid engineand transmission, and half-worn 8.75R16.5 tires,engine speed increased almost 300 rpm at normal high-way speeds.At 55 miles per hour engine speed with the3.07 final drive was 2100 rpm.With the 3.42 finaldrive, engine speed increased to 2400 rpm at 55 milesper hour, and it rose to 2800 rpm at 65 miles per hour,which is where the engine likes to cruise.

Road testing has demonstrated improved responsewhen accelerating to pass or when climbing a hill. If youhave a vacuum gauge, you will notice a higher reading atthe same highway speeds.Also, the vacuum reading drops

less when accelerating or climbing a hill.The higher vacu-um provides quicker and smoother transmission shiftingclosely approximating that of a passenger car. From 55 to65 miles per hour, the 3.42 final drive caused my enginevacuum to increase by more than 1-inch of mercury,which should reduce fuel consumption in the long run.

There is a definite improvement in deceleration brak-ing such as off-ramp slowing or downhill braking.Theimproved responsiveness of the GMC Motorhome withthe 3.42 final drive provides better handling and passen-ger comfort. It gives me the feeling that I’m driving myold 1973 Sequoia with its 455-cid engine instead of my 1978 Palm Beach with its 403-cid engine!

Roy ReitterManchester, Missouri

If I were asked for an off-the-cuff opinion as to thebenefit of the 3.42 final drive, I would say approxi-

mately a 10 percent or better performance increase couldbe expected throughout the operating range. My 1977Palm Beach with a 455-cid engine is far from stock. Ithas Thorley headers, new LT225/75R16 tires and anumber of other goodies. Nevertheless, at 65 miles perhour my engine speed increased from 2500 rpm with the3.07 final drive to 2700 rpm with the new 3.42 finaldrive, and vacuum rose from 11 to 13 inches of mercury.

On a 6 percent uphill grade in third gear and at fullthrottle, the motorhome topped the hill at 45 miles per

hour and 3 inches of mercury vacuum with the original3.07 final drive.With the 3.42 final drive, the motor-home topped the hill at 49 miles per hour and 5 inchesof mercury vacuum.

Starting down a 6 percent grade at 25 miles per hourin second gear with the 3.07 final drive, the motorhomereached the bottom at 50 miles per hour.With the 3.42final drive, the motorhome reached the bottom at 43miles per hour, which is 14 percent slower.

The original torque and horsepower curves for the455-cid engine indicate 2600 rpm is about the idealcruising speed for the engine.With the original 3.07final drive, the engine never reaches that speed withinmaximum speed limits on most highways.With the3.42 final drive, the engine reaches 2600 rpm between60 and 65 miles per hour.

Speedometer correction varies with tire size. Mine wascorrected with a Stewart Warner adapter that is put inline with the speedometer cable.The correction was0.918, but I understand that other corrections range to0.905.The cost of the adapter is about $90.00, and thecorrection can be made by any speedometer shop that hasa cable-turn counter.

Bob DeSaussureSan Rafael, California

I installed the 3.42 final drive and took off on a business trip to Oregon.The motorhome was notice-

ably more responsive going up and down hills, and theincreased engine speed caught my attention.

Upon returning home, I had to accompany my wife to Minnesota to bring back a trailer load of her mother’sbelongings. Like most of us, she really loaded that trailer.My gross combination weight on the trip home was17,000 pounds!

Even though the loaded trailer weighed in the neigh-borhood of 6000 pounds, the 3.42 final drive allowedme to maintain my usual highway speeds, which I won’tmention because they often exceed the speed limit.

The Eisenhower pass was topped 9 miles per hourfaster with the 3.42. Frankly, I tried to destroy it withone of my big engines, but couldn’t. GM did a great job.

Darrel WinterfeldtLongmont, Colorado

Page 14

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