© 2012 Delmar, Cengage Learning

Manual Transmission Diagnosis and Repair

Chapter 72

© 2012 Delmar, Cengage Learning

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

© 2012 Delmar, Cengage Learning

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

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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

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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

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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

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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

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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

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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

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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

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© 2012 Delmar, Cengage Learning

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

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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

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

bearing separator– Reassembling: apply pressure on inside of

bearing only

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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

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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

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Reassemble the Mainshaft• Major steps

– Install gears

– Lubricate parts liberally

– Install synchro hub

– Check end play of assembled parts

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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

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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

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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

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Complete the Transmission Reassembly

• Install shift mechanism• Replace extension housing bushing and seal

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

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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

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Add Lubricant• Important considerations

– Add recommended lubricant before driving the vehicle

– Lubricant level should come to bottom of fill hole

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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