1st post-90 c4 bad bomb?

[The_Geo]

hi all

i have recently acquired a 1990 c4 and have a question.

the car intermittently displays the PDAS and brake warning lights with the alarm horn thing.

reading around, this seems to be either hyd pressure or fluid level.
the issue is more common at 1st start of the day, but occurs at other times as well, usually at traffic lights (so at stop with a foot on the brakes).

the fluid level is ok, but i have yet to check the level sensor terminals.

I suspect the bomb (pressure accumulator) having had a similar issue last summer with my 89 audi 200 10v.

in the 964 3 pumps of the brake pedal is enough to start the pump and 6 generaly lights up the warning lamps. In the audi the norm is 15-20 (should be 40) pumps of the pedal but the hydraulic pump is belt driven so providing constant pressure.

the question is, with a good bomb, how many pumps should the system be expected to provide brake boost pressure for, before the pump fires or the lights light up?

failing that, am i on completely the wrong track and suffering a pressure bleed off somewhere in the diff lock system?

other facts are:
the pump stops and starts, so the relays appear good
the plastic fluid feed pipe has not melted
there is no fluid loss in the system

I eagerly await your words of wisdom

Geraint

[964RS.]

Geraint,

Firstly check that the fluid level is to the top, i.e. the seam on the reservoir, AFTER you have been pumping the brakes. Then check the level sensor by making/breaking the connection to simulate full/empty reservoir to eliminate the sensor.

It does appear to be a soft pedal so I would bleed all 8 callipers and and get plenty of fluid through them.

Check your brake pad thickness whilst you are down there in case they need replacing too.

3 pumps is correct to get the pump actuated and about 6 pumps to get the warning signals on.

[The_Geo]

Thanks for that,

So I am getting paranoid and applying Ingolstat theory to Zuffenhausen products.

Nice to now that it's "normal"

Geraint