General

The Porsche 911 Carrera transmission assembly houses the forward and reverse gears and the differential, also known as the final drive.

This section covers replacement of the differential flange seals. This does not require disassembly of the differential. Disassembly of the differential requires special tools and knowledge, and is beyond the scope of this manual.

Special tool

^ The use of a special seal installer is helpful in performing the procedure described below.

Troubleshooting

The source of driveline vibrations and noise can be difficult to pinpoint. Engine, transmission, drive axle or wheel vibrations can be transmitted through the power train mounts to the car body. Noises from the rear of the car may be caused by differential problems or by faulty wheel bearings or constant velocity (CV) joints. Also check that the tires are correctly inflated and are not excessively worn.

To isolate a vibration or noise problem, speed up the engine in the stopped car to the rpm range where the problem occurs. This eliminates the influence of rotating driveshafts and will help indicate if the problem is caused by an engine condition.

Drive the car at the speed where the problem occurs, then shift to different gears to see if the problem changes with road-speed or engine-speed. Road-speed dependent problems usually indicate trouble in the driveline.

Detach the axle shafts at the differential and then operate the engine at the speed and gear position where the problem occurs. If the problem disappears, then it may be in the axle CV joints or wheel bearings.

Make sure the car is stable and well supported at all times. Use a professional automotive lift or jack stands designed for the purpose. A floor jack is not adequate support.

CAUTION—

♦ Damage to the differential or axle shaft joints can result if the car is run with the wheels off the ground. The wheels hang below their normal height, putting stress on driveline components. Compress the suspension to normal height with jack-stands before running the car.

• Never operate the car with one drive wheel turning at a different speed than the other. Damage to the driveline components can result.

No-load tests with the car stopped or the drive axles disconnected will only give a general idea of the car's performance under the load of normal operation.

For more information on troubleshooting engine or transmission problems, see 100 Engine-General, 310 Clutch, 340 Manual Transmission-Controls and Case, or 350 Manual Transmission-Gears and Shafts. For information on troubleshooting rear axle, wheel bearing or constant velocity joint problems, see 420 Rear Suspension, Axle Shafts.

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