Manual Transmission Diagnosis and Repair

1. Manual Transmission Diagnosis and Repair Chapter 72

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

12. 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

13. 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

14. Replace Worn Bearings • Use a press and support inside of bearing with bearing separator • Reassembling: apply pressure on inside of bearing only

15. 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

16. 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

17. Reassemble the Mainshaft • Major steps • Install gears • Lubricate parts liberally • Install synchro hub • Check end play of assembled parts

18. 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

19. 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

20. 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

21. Complete the Transmission Reassembly • Install shift mechanism • Replace extension housing bushing and seal • Use a seal installer to replace the seal without distorting it

22. 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

23. Add Lubricant • Important considerations • Add recommended lubricant before driving the vehicle • Lubricant level should come to bottom of fill hole

24. 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