Manual Transmission Diagnosis and Repair

© 2012 Delmar, Cengage Learning

Manual Transmission Diagnosis and Repair

Chapter 72


Objectives• Diagnose transmission-related problems• Remove a transmission safely in a professional

manner• Disassemble transmissions correctly• Use presses and pullers competently to

disassemble and reassemble transmissions• Diagnose and service synchronizers• Reassemble and install a transmission in a

vehicle


Introduction• Important considerations in transmission repair– Proper press and puller use – Locating service information• Disassembling transmissions – Requires controlled force– Each transmission has its own peculiarities– Synchronizers are mostly of the same design


Transmission Diagnosis• Clutch problem

– Transmission doesn't go into gear • Transmission failure

– Results from abuse or misapplication– Determine cause before removal

• Some typical symptoms:– Gear clashing during shifting– Hard shifting and jumping out of gear– Unusual noise


Lubricant Checks• Lubricant level

– Checked by removing the fill plug and inserting your little finger inside the hole

• Check for leaks– Front and rear seals– Any switches– Plug or vents– Gaskets

• Oil leakage can result in transmission failure


Transmission Removal• Major steps

– Removing a transmission can be dangerous• Drain gear oil before installing jack • May be necessary to remove exhaust pipes

– Disconnect battery– Remove speedometer cable– Disconnect external shift linkage– Remove and clean transmission

• Identify transmission before ordering parts


Transmission Disassembly• Major steps

– Check service manual before disassembling– Look for damage

• Gears develop normal wear pattern with use– Remove front bearing retainer and snap rings– Remove countershaft and mainshaft

• Mainshaft removed from rear or top of transmission

– Remove the input shaft• Be careful not to damage gears


Disassemble the Mainshaft Assembly

• Major steps– Lay parts out as they are disassembled

• Keep parts in order– High-gear synchro clutch hub

• Held on mainshaft with a snap ring• Remove snap ring with snap ring pliers

– Press or puller pulls synchronizer clutch hub


Synchronizer Service• Synchronizer will be

reused– Scribe line on

outside to reassemble in same position

• Some are marked from factory

• Look for wear – Gears and shift

sleeves


Synchronizer Inspection• Best way to tell if synchro is not working

– Test-drive the vehicle• Worn synchro

– Causes gear clashing• Inspect synchronized gears

– Rarely experience excessive wear• Inspect synchro sleeve

– Even width across length



Inspect Blocker Rings• Inspect brass blocker

rings if they are to be reused– Inside surface should

have sharp edges• Push blocker ring

against polished tapered surface on gear that it rides on– Should grab against

chrome surface


Inspect Input Shaft and Mainshaft

• Inspect mainshaft splines– May be twisted from abusive driving– Twisted spline prevents drive shaft slip yoke from

sliding in and out of transmission• Inspect drive gear for VSS or speedometer

– Located on the output shaft– Rarely suffers damage– A special puller is available to pull these gears


Replace Worn Bearings• Use a press and support inside of bearing with

bearing separator– Reassembling: apply pressure on inside of

bearing only


Reassemble the Transmission• Before assembling

– Locate and assemble any new replacement parts• Two gears operating in mesh

– Create wear pattern • Gear is replaced

– Corresponding gear also replaced– Using an old gear with a new gear can result in

unacceptable gear noise


Reassemble the Synchronizers• Reassemble

synchronizer hub parts– Three inserts are

held in place with a round spring

• Install springs so they rotate in opposite directions


Reassemble the Mainshaft• Major steps

– Install gears– Lubricate parts

liberally– Install synchro hub– Check end play of

assembled parts


End Play• Thrust washers

– Control end clearance– Determine where gear

will be positioned• Check gear clearance

after all gears are assembled– Adjust clearance by

changing thickness of snap ring


Needle Bearing Installation• Needle bearings are

sometimes caged– Can also be loose

and installed one at a time

– Count needle bearings during disassembly

• Service manual– Specifies number of

needle bearings


Install New Gaskets• Purchase a new transmission gasket set

– Gaskets are not reusable• Gasket working fine previously could leak after

reassembly– Replacing this gasket would be a complicated

repair • Would be done at no charge to the customer


Complete the Transmission Reassembly

• Install shift mechanism• Replace extension housing bushing and seal

– Use a seal installer to replace the seal without distorting it


Install the Transmission• Major steps

– Be sure clutch fork is properly seated on its pivot– Align transmission with engine– Shake transmission while rotating it back and

forth– Install bolts in transmission– Torque to specifications


Add Lubricant• Important considerations

– Add recommended lubricant before driving the vehicle

– Lubricant level should come to bottom of fill hole


Test Drive• Important considerations

– Be sure shifts are smooth in all gears– Neutral gate should be accurately aligned– Check outside of transmission for leaks after

returning to shop

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Manual Transmission Diagnosis and Repair