928 psd locking diff all the time..
 

Ok, removed transmission/torque tube to replace torque tube bearings.. etc etc.. once it was all refitted and i went to drive the diff was locking and making a clicking noise.. went through and bled psd system as per instructions but cannot seem to get the diff not to lock.. im completley stumped, if i bleed the slave cylinder the wheels become unlocked but as soon as i switch the igntion off/on the diff is locked again, have checked/swapped relays and replaced the pressure switch.. any suggestions, tester shows up no faults..

seen this 2x before: incorrect fluid (no LSD additive). find an LSD additive: GM sells some, so does Redline. Try that: $10 fix.

I havnt changed the diff oil at all, nor do i believe its a problem... the PSD is locking the diff, as soon as i bleed the slave cylinder the wheels become free again.. forgot to mention this is a 1990 so i dont think it has an LSD. The PSD light is not active though when the diff is locked so it has me stumped..

oh, sorry, I read your post too fast.

im thinking the slave cylinder is faulty and locking diff..

no takers.........

Divide and conquer, pick a stage in the system and check the "status", ie if you have pressure to the slave cylinder, then the slave is doing what its supposed to and the problem is in the other direction. Maybe disconnect the line to the slave and hook the line to a pressure gauge and see what is going on.

Thats my wild assed guess.