Problem with diff seemingly locking up
07-07-2024, 02:47 PM
#46
Rennlist Member
Thread Starter
Just put my 928 on jack stands for the next month or so whilst I plan to escape the summer heat for a month or so. I then removed the rear dirver's side wheel and then the rear splaash guard to expose the PSD unit. Pleased to advise that the level was exactly where I set it a short while back thus concluded that nothing is leaking and my repairs to the hydraulic system were successful.
My conclusions from this event:
1. Changing the fluid regularly is good practice but it is not enough.
2. At some point the slave cylinder needs to be pulled and inspected - not sure what that interval should be but would start on the basis of 10 years.
3. If it has not been done previously change the isolation boot built into the body of the diff.
4.Inspect the bore of the slave cylinder for any signs of corrosion.
5.The linings on the PSD clutch plates last a good long time but not forever. Pulling the PSD unit out of the diff is not difficult and inspecting the clutch plates for wear is not a difficult job. The special tool that measures this wear is not commonly available and a visual inspection is an alternate approach if such is not available. So if the PSD system has not been touched for 20 years or more that may be a good time based interval to check for clutch plate wear. It seems that the plates are considered worn out when the lining thickness has worn from 1mm to 0.5mm. On my clutch plate pack from my 90S4 that came to the rescue that had covered about 120k km had no signs of measurable wear
6. There are two variants of the system- the 90 [and91?] models have 10 plates and the later [GTS] models have 8 plates with slightly thicker linings. I covered the dimension in the body of this thread.
All in all a very imrpessive piece of kit I reeckon.
My conclusions from this event:
1. Changing the fluid regularly is good practice but it is not enough.
2. At some point the slave cylinder needs to be pulled and inspected - not sure what that interval should be but would start on the basis of 10 years.
3. If it has not been done previously change the isolation boot built into the body of the diff.
4.Inspect the bore of the slave cylinder for any signs of corrosion.
5.The linings on the PSD clutch plates last a good long time but not forever. Pulling the PSD unit out of the diff is not difficult and inspecting the clutch plates for wear is not a difficult job. The special tool that measures this wear is not commonly available and a visual inspection is an alternate approach if such is not available. So if the PSD system has not been touched for 20 years or more that may be a good time based interval to check for clutch plate wear. It seems that the plates are considered worn out when the lining thickness has worn from 1mm to 0.5mm. On my clutch plate pack from my 90S4 that came to the rescue that had covered about 120k km had no signs of measurable wear
6. There are two variants of the system- the 90 [and91?] models have 10 plates and the later [GTS] models have 8 plates with slightly thicker linings. I covered the dimension in the body of this thread.
All in all a very imrpessive piece of kit I reeckon.
