TS-05, Troubleshooting - Manual Transmission

Introduction

This troubleshooting guide is intented to help identify and repair manual transmission problems. The following is a list of problem symptoms discussed in this guide:

Rattle from the rear of the car at low RPM.

Possible Causes
Checks
Procedure
5th Gear This is a fairly normal problem, one that Porsche is aware of, and refused warranty claims on. Apparently, 5th gear has more clearance, and hence more play on the transaxle mainshaft than the other gears and tends to rattle at low RPM. 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

Noise from drive train with engine idling and clutch pedal depressed.

Possible Causes
Checks
Procedure
Clutch release bearing or pilot bearing Usually a high pitched squealing or grating noise. There's really no way to identify this problem positively without disassembling the clutch. Use the Clutch Replacement procedure to disassemble and inspect but, exhaust all other possible causes first as this is a tedious procedure.

CLUTCH-01

Noise from drive train with engine idling, clutch pedal not depressed, and transmission in neutral.

Possible Causes
Checks
Procedure
Clutch Disc If the car is equipped with a rubber centerd clutch, the rubber eventually rots and disintegrates causing noise (usually a thumping noise) which is transmitted along the drive line. There's really no way to identify this problem positively without disassembling the clutch. Use the Clutch Replacement procedure to disassemble and inspect but, exhaust all other possible causes first as this is a tedious procedure.

CLUTCH-01
Clutch release bearing or pilot bearing Usually a high pitched squealing noise. Again, There's really no way to identify this problem positively without disassembling the clutch. However, you may be able to narrow down the location using a mechanics stethoscope. Use the Clutch Replacement procedure to disassemble and inspect but, exhaust all other possible causes first as this is a tedious procedure.

CLUTCH-01
Torque tube bearings Usually a high pitched squealing noise or grating noise. Try using a mechanics stethoscope to pinpoint the location of the noise. If you determine that it is most likely the torque tube bearings, replace the torque tube or rebuild using the Torque Tube Revoval, Rebuild, and Installation procedure.

TRANS-05
Drive Shaft to Transaxle Input Shaft Coupling This is not a very common problem but, I have heard of at least one instance where the bolts that secure the coupling came loose and the coupling started rattling. This occurred shortly after a clutch replacement (which requires removal of the transaxle). So, the coupling bolts were not properly torqued during the coupling installation.

N/A
Transaxle While noise in the drive train under the condition specified can come from the transaxle it is not common. Normally, transaxle noise in this condition comes from one of the input shaft bearings. The only permenant fix is to rebuild the transaxle.

N/A

Noise from drive train during normal driving.

Possible Causes
Checks
Procedure

Before you start trying to troubleshoot this problem, you should try to eliminate as many potential causes of drive line noise as possible. So, you should first allow the car to idle with clutch engaged (clutch pedal not depressed) and the transaxle in neutral. If the noise is NOT present in this condition, it eliminates the clutch disc, clutch release and pilot bearings, torque tube bearings, and transaxle input shaft coupling as possible causes of the noise.

CV Joints Frequently, noise from the rear end is caused by the CV Joints. And, it's most common for this to be due to lack of lubrication. You'd think that the grease in the CV Joints would not disappear unless the CV Joint Boot is bad. However, it happens. Anytime you have a noise that you narrowed down to the rear end of the drive train, your first action should be to rebuild/repack the CV Joints using the CV Joint General Information, Removal, Installation, and Maintenance procedure.

SUSP-01
Rear Wheel Bearings The next most common cause of rear drive line noise is bad wheel bearings. If the noise changes pitch, disappears during cornering, or only appears during cornering, the most likely cause is the wheel bearings. The wheel bearings should be replaced using Rear Wheel Bearing Replacement - Steel Trailing Arms or Rear Wheel Bearing Replacement - Aluminum Trailing Arms.

SUSP-09
SUSP-11
Transaxle If you have eliminated the CV Joints and Rear Wheel Bearings as possible causes of the rear drive line noise, it's time to turn to the transaxle. There are approximately 10 bearings in the transaxle including the front and rear needle bearings, the individual gear needle bearings, the four point ball bearing in the transmission case, and the tapered roller bearings for the two flange shafts. Any one or more of these bearings going bad can cause can cause noise from the transaxle.

The only bearings that are replaceable without a great deal of disassembly are the axle flange shaft roller bearings. However, I don't have a procedure for that yet. As far as rebuilding the transaxle, it requires a number of special tools to press component onto and off of the transaxle shafts and to set pre-loads. So, a complete rebuild is best left to a professional transmission shop.

N/A

  • Transmission difficult to shift or will not engage into gear.

    Possible Causes
    Checks
    Procedure
    Clutch Disc Refer to TS-04, Troubleshooting - Clutch

    TS-04
    Pressure Plate Refer to TS-04, Troubleshooting - Clutch

    TS-04
    Transaxle Bad sychros in the transaxle will cause difficult shifting. 944s are notorious for 2nd gear and sometimes 3rd gear sychros to go bad. If the transmission is difficult to shift when cold, particularly in second gear, and the shifting improves as the transaxle warms up, it's due to a bad synchro. The only permanent solution is to rebuild the transaxle. However, switching to a synthetic gear oil in the transaxle will most likely improve the shifting.

    N/A
    Shift Lever or Shift Linkage A worn and sloppy shift lever or shift linkage can make shifting difficult. Inspect the shift lever and shift linkage and make repairs as necessary.

    TRANS-07

    Clark's Garage 1998