gjvander

Hi,

I have some fundemental questions about how the C4 brake system works.

The way I understand it there is a reservoir that feeds the high pressure pump. The pump builds 180 bar pressure and sends it to the accumulator. The accumulator spits the fluid in two and sends it to the diff lock control system and the ABS unit. Still right so far?

I think Adrian mentions that the accumulator can't drop to less than 80 bar or something like that. Basically you can't bleed of all the pressure in the accumulator, even with booster pump disconnected.

My question is how does the accumlator work (inside) so it can't drop to zero pressure?

I have had the pressure transducer in the booster pump fail on me a few months ago, and let me assure you the C4 does not stop very well without that pump running.

I have a full set of manuals, so feel free to refer to those.

Regards,

Geo

Adrian

Dear Geo,
The accumulator is not mentioned in the manuals. An accumulator is divided into two parts. The pre-charge chamber and the pressure fluid chamber. Holds 300cc of fluid. The pre-charge chamber is separated from the main chamber by a rubber diaphrapm. The pre-charge chamber is charged up with nitrogen at the factory and it is sealed. The fluid in the main chamber is always kept at a minimum pressure of 80 bar (until the charge gradually falls away).
This system has nothing to do with the ABS.
Ciao,
Adrian
964C4

gjvander

Thanks for the reply Adrian.

Which system is the accumulator part of then? Just the differential hydraulic actuators?

Also, I am busy dropping the engine and transmission. I think I am going to have to disconnect the diff actuator lines. Where is the best place to do that? At the gearbox, or maybe a few inches away where the bracket for the two hard lines are?

Regards,

Geo

Adrian

Dear Geo,
The accumulator is part of the hydraulic brake boost system which also supplies the pressure fluid to the traction control system. The ABS is part of the brake system not the boost system.
Ciao,
Adrian
964C4