Manual Transmission Diagnosis and Repair
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Transcript of Manual Transmission Diagnosis and Repair
© 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
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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