'88 5KSQ (Type 44) Brake Problems

[Ameer Antar]

pedals going to the floor is a very dangerous, esp. if you had to pump the 
pedal for a sudden stop. I don't think Audi would design a system that 
would fail like that just if the hydraulic system has a leak [internal or 
external]. A safe design would allow you to brake, but require more effort 
[this means more force, not pumping], when something happened to the power 
assist. Basically there ire two forces which push the m/c piston in it's 
cylinder. The first is mechanical pressure from the pedal. The other is the 
brake fluid pressure in the lines going to the brakes. If there is a loss 
of brake pressure in the lines or air in them [air compresses, liquid 
doesn't] the piston will fall back to far and the pedal goes to the floor 
when you press on it. This can also happen if brake fluid can get past the 
m/c piston back into the reservoir. The servo is basically a rod which 
connects the pedal to the m/c. It also has a piston attached to it inside 
and hydraulic pressure [pentosin] is used to pressurize the servo, 
assisting in the pedal pressure applied to the m/c. So, in other words, the 
m/c should not let the pedal travel that far, unless of course someone 
changed the length of the pushrod which connects the servo to pedal. 
Culprits can be leaky brakes, lines, bad flex hoses, air in the system, and 
finally the m/c, but all other problems should be fixed first.

The way to tell if you have bad assist is if there requires lots of pedal 
pressure [steady not pumping], leaks, large flow of fluid from the servo 
return line at idle, and loss of brake assist after 10-20 pumps w/ the car 
off. Remember, servo asssist is just an assist, not what actually applies 
the brakes. good luck.

At 06:44 PM 9/28/00, you wrote:
>Christopher-
>
>My car (885ksq) does the SAME thing... I think it's the Bomb.  I know you
>said yours is new but, it could still be bad.  How "new"?  I've heard of
>people's going bad after only a year.  I even heard of a guy thinking he
>could buy a "good" used one for $5.  I hope that wasn't the one you bought.
>
>Here's what my car does:
>At IDLE, if I hold the pedal down, it will go (slowly) all the way to the
>floor, and pulsate slightly on the way down.  Then the brake warning light
>will come on.  I think if you connect your switch, it will do the same.  If
>I am running the car at >2krpm, it will NOT go to the floor.  Then, if I
>shut the car off, the pedal goes rock hard instantly, and will NOT go to
>the floor.  I guess it COULD be the MC, I've just always figured that since
>my bomb gives dead symptoms, that it's the cause of the pedal being able to
>go all the way down.  It doesn't totally make sense to me where the fluid
>is all going when the pedal goes down, but then again, it doesn't make
>sense to me that you should be able to consume the accumulated fluid in a
>good bomb with the engine off by pumping it either...  SOMEBODY correct me
>too if I'm wrong about all this.  And Chris, if your bomb IS STILL GOOD,
>(you get about 20 pedals out of it with the engine off), then let me know,
>because that would indicate that our problem is servo or MC.  Hell, maybe
>it's the damn pump.  I guess I'm not sure.  I bet that was of help!?!
>
>Thanks,
>Matt
>
>
>At 01:12 AM 9/28/00 GMT, you wrote:
> >The brake pedal on my '88 5KSQ will slowly go to or near the floor if I 
> hold
> >pressure on it.  The warning light switch on the servo for the Autocheck
> >system is disabled.  The car has a new pump and pressure accumulator
> >("bomb").  In a normal car, I would suspect the master cylinder.  But what
> >is the "brake servo"?  That is the thing between the pedal and the master
> >cylinder.  What does it do?
> >
> >At about 120K miles, I am ready to replace the master cylinder.  No 
> rebuilds
> >for this critical part.  Should I also replace the servo?
> >
> >
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>----
>88 5ksq
>Matthew Caprio
>Austin, TX
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