Late Model Mopar Transmission Tech, Part 1© MoparMax Magazine 2012

Words by Richard Kratz photos by Richard Kratz

According to JD Powers, back in 1980 more than 35% of new cars purchased in America came with manualtransmissions. Depending on source to which you listen, in 2012 that’s down to 5 - 7%. Cars with manualtransmissions just don’t sell well any more.

You don’t have to look much further than late model Mopars to see proof of the dominance of automatictransmission cars in the marketplace. Whole model lines don’t even offer a manual transmission as an option.Chrysler 300, Dodge Charger and Magnum, not a one with a stick shift on the options list; the only late modelMopar V8 you can buy with a manual transmission option is the Challenger.

Modern automatics are vastly more efficient than they were back in the day. Additional gears, overdrive, lockuptorque converters and computers have reduced the miles per gallon gap between manual and automatictransmissions, an important consideration for today’s buyers. But all of this additional complexity is notnecessarily good for gear heads and performance enthusiasts.

MoparMax’s 2007 Dodge Magnum SRT8, the Maulin’ Magnum, has been a rolling lab experiment for the lastyear or so. Fifteen months ago the car was factory stock. Since then it’s had a 50 hp shot nitrous kit, then wentback to normally aspirated and the rear end was strengthened and steeper 3.55 gears installed. Then a 150 hpshot nitrous upgrade was installed, then that was removed and a Magnuson Magnacharger kit was bolted on.

We’ve experimented with our Diablosport Trintity including the various shifting modes and raising the shiftpoints.

In the process of all this, the Maulin’ Magnum has racked up 49,000 miles and over 400 laps at the drag strip. Infact, as we’re writing this the Magnum is within one round win of first place in its class in two different racingseries, PSCA and WCHRA. In other words, she’s been used hard and the data logs started to indicate that thetransmission was tired so it was time to service it. We’re breaking this article into two parts, in this first partwe’re going to cover upgrading the valve body and in part two we’ll cover the transmission itself and torqueconverter upgrades.

First, an overview of the transmission. The NAG1 is actually a Mercedes transmission, dating from whenDaimler-Benz owned Chrysler and is found in 2005 to 2012 Chrysler, Dodge and Ram vehicles. In Mercedescode the transmission is called the W5A580 or WA580 transmission. The Chrysler nomenclature breaks downas follows:

N = NewA = AutomaticG = Gearbox1 = 1st Generation

Or for the Mercedes designation:

W = Transmission with a torque converter (we have no idea, must not translate from German)5 = Five forward gearsA = Automatic580 = Maximum input toque of 580 Newton meters (428 lb. ft.)

Advantages to the NAG1 include its small size, light weight for its torque capacity, wide gear ratios andoverdrive. The gear ratios on the NAG1 start steep and work up to a relatively small overdrive:

1st gear: 3.592nd gear: 2.193rd gear: 1.414th gear: 1.005th gear: 0.83

Chrysler built NAG1 transmissions at its Indian Transmission Plant II in Kokomo, Indiana. The transmissionhas three planetary gear sets which have four planetary gears each. The transmission utilizes unusually high linepressures, double that of most transmissions at 300 PSI. The torque converter is a lockup type with a multi-platefriction plate/steel plate design.

An electronic Transmission Control Module (TCM) commands the transmission. The TCM is adaptive and hastrim tables that allow the computer to adjust the transmission’s shift characteristics to your driving style.

So the good news is that the NAG1 is a fairly strong, yet relatively lightweight unit. It is a complex transmissionand even if you know how to tear down and rebuild a 727 transmission we urge you to think long and hardbefore tackling the NAG1. It’s a beast of a different nature.

We headed down to our good friends Joe and Mike Piraino, proprietors of Westminster PerformanceTransmission in Westminster, California. Joe and Mike know more than a little about the NAG1 transmission,they have the contract to service police Chargers from various agencies and have learned how to make theNAG1 stand up to the torture the police users throw at it. Joe and Mike build some insane transmissions for

equally insanely fast cars, including their own twin turbo six-second dragster. These guys know engineering aswell as transmissions; their dragster has won “Best Engineered” not once, but twice at the NHRA WinterNationals in Pomona, California.

Our main complaint was inconsistent shifting at the track. Contributing Editor and race driver for the Magnum,Alex Rogeo, said sometimes the car seemed to linger for a fraction of a second during a shift. This was causingus to lose rounds.

After looking at our data logs, Mike told us that we needed to start with replacing the valve body. The valvebody is a wonderfully complex device; in essence it’s a hydraulic computer (although the NAG1 like mostmodern transmissions is a hybrid hydraulic/electronic). Marvelously complex small passages with ball checkvalves and multiple pressure regulating mechanisms, some using pistons and springs in small cylinders andother using electric solenoids, all work in concert to determine when and how hard the transmission should shiftgears. When you look at the schematics and blue prints for the NAG1 valve body you’re not sure if it’s for atransmission or a NASA probe to Mars.

Early NAG1 transmission valve bodies, prior to about 2010, are known to develop a leak in one of theregulating piston’s cylinders. This causes confusion in the transmission during shifting and we saw it as an oddtrace where at the shift peaks the RPM just kind of plateaus momentarily. Chrysler has issued a new partnumber for the valve body, RL108213AB and this valve body has an improved designed with a more wearresistant cylinder for said piston. Careful online hunting led us to onestopoem.com where we purchased thevalve body for under $500.

Mike and Joe also told us that we needed to replace the transmission adaptor plug which is the point where theelectrical wires enter the transmission. This adaptor is located just above the transmission pan on the frontcorner passenger side of the transmission and you have to disconnect it anyway to remove the valve body. Thefirst generation of these adaptors is a common failure point and causes leaks. It if yours isn’t leaking now, itvery well may in the future so you might as well replace it now. It’s not an expensive part, about $15. The partnumber you want is: 2035400253.

Replacing the valve body is a fairly simple and straight forward job, although it can be a very messy job. Inaddition to the replacement valve body and adaptor plug. You’ll want to pick up a new filter which usuallycomes with a new pan gasket.

We had previously upgraded our valve body to so called “blue top” solenoids. There are six electric solenoids inthe NAG1 valve body, and the Chrysler version uses slightly different solenoids then the Mercedes version. The“brown top” Chrysler solenoids control internal line pressure and modulator pressure and produce slower, softer“American” shifts then the European tuned Mercedes blue top solenoids. The difference in shiftingcharacteristics is marked especially on the downshifts which are very firm and fast with the blue tops. So wesimply swapped the blue top solenoids into the new valve body. Then we reinstalled the valve body into thetransmission, replaced the adapter plug with the new one, installed the new filter and reinstalled thetransmission pan. The latest part number as of the date of this article is 2402700089.

Once the valve body swap was complete and everything buttoned up tight, it was time to refill the lost fluid.Chrysler calls for ATF +4 fluid so that’s what we used. The tricky part is getting the right amount of fluid intothe transmission. The NAG1 is extremely sensitive to fluid levels mainly due to its unique, and some say odd,method for determining transmission overheating. In the middle of the valve body is a little floating pistonvalve. As the transmission fluid heats up it expands raising the fluid level in the pan. If the fluid gets too hot andexpands too much the floating piston valve rises up far enough to contact its valve seat and closes which signalsthe transmission controller that it’s overheating and the TCM goes into limp mode. So over full is very badunless you like limping home.

Conversely, the NAG1 hates low fluid levels and can be damaged fairly quickly if the level is too low. So underfull is very bad. But you can’t just stick a dipstick into the transmission and see if you need more or less fluid.Mercedes calls for a special tool made by Miller, part number 9336A. This special dipstick is marked inmillimeters and to use it you need the temperature/fill level chart from the service manual (or find it online) andyou need to know the exact temperature of the transmission fluid. For the temperature, when we first upgradedthe solenoids we left the Miller tool in the fluid for a minute and then pulled it out and used our laser tiretemperature gauge to read the end of the dipstick in the fluid. Hey, it worked, especially since the car lacks atransmission temperature gauge or function. Knowing the fluid temp you note how many millimeters from thetip the fluid is registering on the dipstick and cross reference the two on the fill chart.

To make it easier to get close to the correct fluid level we had carefully collected the drained fluid and measuredit, noting that a little bit less than four quarts drained out. So we started by filling with three quarts, then withthe engine idling and the Miller tool we finished the fill.

With the new valve body that weirdness on the 1-2 and 2-3 shift was gone and the shifts were much quicker andmore decisive. However, we still had weirdness in the 3-4 shift and the car was producing strange quarter milepasses, running fast in the first eighth mile and slow in the second or vice versa. We definitely had somethingstrange in the transmission. So it was back to Westminster with the car and time to yank out the transmissionand rebuild it. And of course, beef it up and make it stronger. So watch for part two of this story on rebuildingand upgrading the NAG1 transmission and modifying the torque converter.

CONTACT:

Westminster Performance Transmissionwww.WestminsterTransmission.com7032 Westminster AveWestminster CA 92683(714) 897-6611

CAPTION: Remove the transmission cross member (on right side of above image) to gain access to the panbolts. Be sure to support the transmission tail shaft.

CAPTION: With the pan removed you can see the valve body with the filter below it. You have to remove thetransmission adaptor plug before you can unbolt and remove the valve body.

CAPTION: The arrow points to the transmission adaptor plug that you want to be sure to upgrade to the newestpart number (see the text for details). If it didn’t leak before this, it would if you didn’t replace it now.

CAPTION: Joe (left) and Mike Piraino, proprietors of Westminster Performance Transmission, look over theNAG1 valve body. 1) This white disk is a floating piston that rises and falls with the transmission fluid level asit heats and cools. If the fluid overheats it will expand enough to make this disc valve close against its seat andput the transmission into limp mode. 2) Note the blue tops on these solenoids, which gives them their commonname. This Mercedes part makes up and down shifts significantly faster and firmer. 3) This is where thetransmission adaptor plugs inserts.

CAPTION: Joe is pointing to the seat in the transmission case where the floating piston/disk will seal in theevent of transmission overheating or if you overfill the transmission fluid. Note the two holes to the right ofwhere Joe is pointing, these passages are blocked and unblocked by the valve body and control the torqueconverter’s lock up clutch.