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Brake boost pump


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I'm not clued up enough on Porsches, that's why I'm at these forums where are people who can help. :)

Just noted that the 964 and other porsches (C4 stuff) use a hydraulic boost pump (high pressure pump) for brakes and handle the diffs. This looked like an ideal item for another project I am on.

I was wondering if anyone can describe the operation of the pump and how it fits into the who whole braking setup. Also, let me know if I am running in the wrong direction with this, but it's for removing vacuum assist for brakes.

Here's a pic I found of the item. It's in the upper right, above the battery:


Edited by 2226cc
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I'm transforming my C4 to be 2WD keeping the original ABS and traction control units.

I try to write a correct english, I apologize if the words are not the good ones !

Here is a photo while the C4 was dismantled :


On the right behind the battery you can see the ABS unit which has the pump and tank included. The things which can be tuned here are : the pressure sensor which works at different pressure on C4/RS than on C2/RS America/Turbo. Changing the sensor means 4 or 5 bars more. The other thing to tune is a very complex thing : ABS control unit (which also manages a large part of the traction control).

in the cockpit, in the console are the gyroscopes, behind this :


The gyroscopes are here under the '1109' wire :


The control unit uses these two sensors with the ABS sensors to determine the lost of traction in any direction and try to correct it using longitudinal (front/rear) and transversal (for the rear only) tork distribution + playing with brake at each wheel.

I have a friend in our team working on the de-assembled code to reprogram it, it looks complicated (more than the motronic).

The brake are naturally managed by the ABS unit while the tork distribution is managed by these electro valves :


You can find them on the left in the front compartment.

There are two outputs :

- one for the rear left/right distribution (working on the limited slip pressure)

- one for the rear/front distribution (locking the visco)

I found a way to bypass the rear/front one.

There is also a compressor, which is at the very front of the car, but I didn't take any photo of it.

This compressor works the same way the ABS compressor does. There is also a pressure sensor but I wouldn't recommend to modify it, it can result in very violent transitions for the VC.

Hope this will help !

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