RE: Hydraulic Pressure Accumulator

[paul.heneghan@bbc.co.uk (Heneghan,Paul)]

From: Simon Allcorn <SALLCORN@softa.co.uk>

>I sent a message to the list yesterday after pumping my brake pedal to
>see how many times I could do it before it went 'hard' (3-4). Everybody
>on the list thinks this suggests a worm out bomb BUT when I look under
>the bonnet (hood) there is not a pressure accumulator on the car ! (87
>CQ RHD). Does anybody know which Audis have bombs and which don't ? 

I don't think 80s or Coupes have the bomb - just the 100s.  Is your 
 brake servo operated by vacuum (large 25cm diameter drum attached to 
 master cylinder) or hydraulics (in which case you will have a feed to 
 the hydraulic servo coming from the hydraulic/PAS pump via the 
 accumulator/bomb).

If your car has a vacuum servo (like my 1984 80q), then with the engine 
 off, you will lose vacuum assist after a few presses.  This means that 
 you have to supply all the braking effort yourself and makes the pedal 
 seem harder (i.e. more difficult to press).  This is the standard test 
 to check that the servo is working.


>I used to own an 82  Golf (Rabbet) with the 1500 engine and a friend
>had a Jetta (a Gold with a Trunk) with the same engine and I remember
>noticing that he had a bomb (small green ball about 4' dia).

This 'bomb' will be a vacuum storage bomb, not a hydraulic (>1000psi) bomb.

>The reason
>I say this is that the Jetta/Golf should have identical braking systems
>(as far as I know) given the same engine size, so why did one have a
>bomb and the other not ?

My 80q has a vacuum bomb in the boot - I think it stores vacuum for the 
 central locking (or maybe it's for the diff locks?).  You probably 
 have one of these as well.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1983 Audi 100 Avant