Troubleshooting - Manual Transmission

Introduction

This troubleshooting guide is intended to help identify and repair manual transmission problems. Symptoms covered:

• Rattle from the rear of the car at low RPM
• Noise from drive train with engine idling and clutch pedal depressed
• Noise from drive train with engine idling, clutch pedal not depressed, and transmission in neutral
• Noise from drive train during normal driving
• Transmission difficult to shift or will not engage into gear

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Rattle From the Rear of the Car at Low RPM

Possible Cause	Checks	Procedure
5th Gear	Fifth gear has more clearance and play on the transaxle mainshaft than the other gears, causing it to rattle at low RPM. This is a known characteristic of the design. The type of transaxle fluid used affects the amount of noise — a good synthetic gear oil will reduce the noise and in some cases eliminate it completely.	N/A

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Noise From Drive Train With Engine Idling and Clutch Pedal Depressed

Possible Cause	Checks	Procedure
Clutch release bearing or pilot bearing	Usually presents as a high-pitched squealing or grating noise. There is no reliable way to confirm this without disassembling the clutch. Exhaust all other possible causes first — clutch disassembly is a tedious procedure.	CLUTCH-01

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Noise From Drive Train With Engine Idling, Clutch Pedal Not Depressed, and Transmission in Neutral

Diagnostic tip: Before investigating further, allow the car to idle with the clutch engaged (pedal not depressed) and the transaxle in neutral. If noise is absent under this condition, it eliminates the clutch disc, clutch release and pilot bearings, torque tube bearings, and transaxle input shaft coupling as possible sources.

Possible Cause	Checks	Procedure
Clutch Disc	A rubber-centered clutch disc — fitted to some 944s from the factory — will eventually deteriorate, causing thumping noise transmitted along the driveline. There is no way to confirm this without disassembling the clutch. Exhaust all other causes first.	CLUTCH-01
Clutch release bearing or pilot bearing	Usually a high-pitched squealing noise. A mechanics stethoscope may help narrow the location. There is no way to confirm without disassembly. Exhaust all other causes first.	CLUTCH-01
Torque tube bearings	Usually a high-pitched squealing or grating noise. Use a mechanics stethoscope to help pinpoint the location. If the torque tube bearings are the likely cause, replace or rebuild the torque tube using the Torque Tube Removal, Rebuild, and Installation procedure.	TRANS-05
Drive shaft to transaxle input shaft coupling	An uncommon problem. At least one case is known where coupling bolts came loose and the coupling began rattling — occurring shortly after a clutch replacement when coupling bolts were not properly torqued.	N/A
Transaxle input shaft bearing	Transaxle noise under this condition is not common. It typically originates from an input shaft bearing. The only permanent fix is to rebuild the transaxle.	N/A

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Noise From Drive Train During Normal Driving

Diagnostic tip: Allow the car to idle with the clutch engaged and the transaxle in neutral first. If noise is not present under this condition, it eliminates the clutch disc, clutch release and pilot bearings, torque tube bearings, and transaxle input shaft coupling as sources.

Possible Cause	Checks	Procedure
CV Joints	Rear-end noise is frequently caused by CV joints, most often due to lack of lubrication. Anytime noise is narrowed to the rear drivetrain, the first action should be to rebuild and repack the CV joints.	SUSP-01
Rear Wheel Bearings	The next most common cause of rear drivetrain noise. If the noise changes pitch, disappears during cornering, or only appears during cornering, the most likely cause is the wheel bearings. Replace using the appropriate procedure for your trailing arm type (steel or aluminum).	SUSP-09 (steel), SUSP-11 (aluminum)
Transaxle	If CV joints and wheel bearings have been eliminated, the transaxle is the next suspect. There are approximately 10 bearings in the transaxle including front and rear needle bearings, individual gear needle bearings, the four-point ball bearing in the transmission case, and the tapered roller bearings for the two flange shafts. The only bearings replaceable without major disassembly are the axle flange shaft roller bearings. A complete transaxle rebuild requires special tooling and is best left to a professional transmission shop.	N/A

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Transmission Difficult to Shift or Will Not Engage Into Gear

Possible Cause	Checks	Procedure
Clutch Disc	Refer to TS-04, Troubleshooting - Clutch.	TS-04
Pressure Plate	Refer to TS-04, Troubleshooting - Clutch.	TS-04
Transaxle (worn synchros)	Bad synchros — particularly in 2nd gear and sometimes 3rd gear — are a known weakness of these transaxles. If shifting is difficult when cold and improves as the transaxle warms up, a bad synchro is the likely cause. The only permanent solution is a transaxle rebuild. Switching to a synthetic gear oil will most likely improve shifting.	N/A
Shift Lever or Shift Linkage	A worn or sloppy shift lever or linkage can make shifting difficult. Inspect and repair as necessary.	TRANS-07