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Re: 88 5000cstq

I have originally typed this for Jon, but since this is one of those
ever surfacing topics, I've decided to post it to the list.

Jon Meckem wrote:
> Thanks Igor,
> This really helps, I am going to look at the car on Friday.  Just one thing,
> where is the bomb located? And can I check it in the "field"?


1/2 of the bomb is filled with N @~2000psi, the other 1/2 - with
hydrolic fluid (Pentosin 7.1 only!!! No regular AT fluid under ANY
circumstances: big bux to rebuild the whole hydro sys later!). These 2
chambers are separated by a membrane. On a spinning engine P/S pump
creates the same 2000psi of counter pressure, so the two mediums are at
equilibrium. When you hit the brakes you get some MASSIVE stopping force
on those 4 discs, fronts are dual calipered and vented to boot.(Mine are
also crossdrilled in all 4 corners, coz I take the car to a race track).
There is one more advantage to the hydrolic assist vs. conventional
vacuum assist: the brakes do not lose power up until ~30 pumps with the
engine killed. On a conventional car with a vacuum assist you only need 
2-3 pumps to lose assist without the engine running.
All in all, Audis have OUTSTANDING brakes. I would rate only Porche
brakes at the higher level, but then again, the P-car is a family
(cousin) to Audi anyway.

It comes at a cost, though. At about 100kmi you typicaly need to replace
the bomb and either replace or rebuild P/S pump and steering rack.
The cost (assuming that you are handy and believe that the best Audi
shop is your own garage, like most of us do) is approx:
1. the bomb ~$250
2. P/S pump rebuild kit ~$15, + 2 hours of your time if for the first
time (takes me about 40 min now).
3. P/S rack rebuild kit ~$50, + 1/2 of a Saturday.

Here's one way to check the bomb:

1. Release the emergency brake.
2. Turn the ignition ON. The red brake light in the lower centre portion
of the instrument combo should light up. Don't confuse it with the brake
icon in the upper centre window of the diagnostics computer, that one
shows the degree of wear of the brake pads. (Yes, this car has
unbelievable intelligence).
3. Start the car. The brake light should go out immediately. If yes -
the bomb is OK.

If no, check the emergency brake switch, they share the same combo
If the e-brake switch is OK, but the light stays ON - the bomb is bad.
If the light stays on for several seconds after you've started the
engine - the bomb is on it's way down, but you have about 1 year left to
fix it.

Here's another way:

Let the car run for 2 min, allowing it to build the hydro pressure.
Kill the engine and pump the brake pedal, while counting the number of
strokes, till the pedal becomes hard (when all the residual hydro
pressure is gone). 
Anything less than 30 strokes - the bomb is bad.

Here's yet one more way:

Start the engine, let it idle and depress the brake pedal with a firm
and even effort. 
1. The pedal smoothly goes where it's suppose to go and stops dead nuts
as if it has hit a brick-the bomb is OK.
2. The pedal gradualy recedes almost to the floor, with a light
vibration under your foot - the bomb is bad.

The 3rd way takes a trained eye, err foot to tell a bad bomb from a bad
MC. I had goofed up on it the first time - wasted $125 on a new MC,
which I did not need.

Now, if the bomb is bad, but you like the car and the price is right -
screw the bomb. You will go through the bomb, P/S pump and rack
replacement anyhow sooner or later. It is a part of Audi ownership
experience anyway.

Good luck
Igor Kessel
'89 200TQ