sprie

I am in the process of sending away my PSD mechanics from inside the rear wing to get it rebuilt.

My understanding is that the purpose of the PSD is when one rear wheel starts losing traction (i.e. spinning faster than the other rear wheel), the differential gets locked, so that power goes equally to both wheels.

Out of interest, whilst it doesn’t affect any work I do to the car (as I am not going to open up the diff), how does the diff do this?
I know the PSD operates through a single slave cylinder. So my question is what happens inside the diff when the PSD operates the cylinder i.e. how does it lock the diff. I am looking at the parts diagram and I can see a set of discs, which I understand operate as a set of mini-clutches, so how do these get “locked”?

Tom. M

just a swag, but guessing the computer controls the pump to push the "slave" that actuates the arm which presses the psd clutch discs together for more lockup and it varies continuously as needed (determined by the computer and sensors). Can provide from 0 to 100% lockup.

Watching this thread as I need to find a way to actuate my psd (track car) without the issues that Mark A identified using a bolt (as case expands the psd lock changes and is unpredictable).

GregBBRD

Good description of the function.

Good luck with getting it to work, on the track. The stock electronics and hydraulic actuation is way too slow for anything except very long corners, on the race track....most corners are over, before the system can react. Additionally, since the actuation takes time to occur, it's a bit "unsettling" when it begins functioning, in the middle or end of a corner. This causes an instant change to increased understeer....which is already an issue in almost every 928.

In terms of making the PSD work mechanically is a really tough road. The difference between 0% lock and 100% lock is a very small movement....and any change in the temperature of the transmission will change that percentage. A virtually unworkable problem.

If you read my thread on the Extremely Extreme 928, you will see that I hand made a true limited slip, for this vehicle, which also keeps the transmission pump functional, out of existing 928 pieces.
I continue to do this, for other clients, until I have enough time to have a complete custom limited slip made (which has already been paid for.)