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© 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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
© 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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Replace Worn Bearings• Use a press and support inside of bearing with
bearing separator– Reassembling: apply pressure on inside of
bearing only
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Reassemble the Mainshaft• Major steps
– Install gears
– Lubricate parts liberally
– Install synchro hub
– Check end play of assembled parts
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Complete the Transmission Reassembly
• Install shift mechanism• Replace extension housing bushing and seal
– Use a seal installer to replace the seal without distorting it
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Add Lubricant• Important considerations
– Add recommended lubricant before driving the vehicle
– Lubricant level should come to bottom of fill hole
© 2012 Delmar, Cengage Learning
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