Audi A4 brake problem

Hi I've got a problem with an 2002 Audi A4, 1.9TDI: several times now, the brakes have locked on after braking hard. By this, I mean the brakes are jammed on after removing all pressure from the pedal. Forcing the pedal upwards seems to fix this and all is OK again.

My wife took the car into the Audi dealer today (so info is second hand) and they want to:

- replace the vacuum pump

- if that doesn't work, replace the servo.

I can see how the servo could cause this but I don't see how a vacuum pump could possibly generate these symptoms.

Any ideas?

Many thanks Mark

Reply to
MarkF
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If you don't have a clue, why leave it to your wife! Why not phone the dealer or call in yourself. Also why question the dealer? I think they are far more qualified than most hobbyists in a newsgroup. The diagnosis is correct so discuss it with them - they will explain all the technical details to you.

Reply to
John

Oh do shut up you tedious prat.

clive

(hi mark :-) )

Reply to
Clive George

I'm going to do exactly that tomorrow but I'd like to understand the possibly causes first.

I'm sure they are - but I've had some bad experiences with the the motor trade. The last garage who serviced a car for me assured me that they couldn't change the brake pads because a pin had seized and so it needed a new caliper. All very plausible but there weren't any pins in the caliper and I changed the pads without any problem.

Hmmm, not the most helpful post ever.

Reply to
MarkF

Er hi Clive - didn't expect to find you here. Too many wheels surely...

Reply to
MarkF

Bad form n'all, but it just occurred to me : Yup, Tiscali Idiot.

clive

Reply to
Clive George

Still get to spanner the BX sometimes :-)

(and I got the answer here to my last problem (alternator) - the BX list has all but died.)

cheers, clive

Reply to
Clive George

I can't see either of those components giving this symptom, it sounds like they want to replace everything until it's fixed. ie, they haven't got a clue. I suspect something seized, has the A4 got a crosslink from the pedal to the M/cyl? I've known those to seize, but it would be rare on a car this young.

Steve

Reply to
shazzbat

A faulty vacuum pump wouldn't cause the pedal to stick.

Given that the pedal is physically sticking down, then it's either a seized pivot somewhere, the master cylinder, or the servo.

Reply to
moray

I'll second that. It's very unlikely indeed, if not impossible to be the pump.

Reply to
Chris Bartram

let the dealer both diagnose and do the work. If it doesn't cure it then get your money back!

Reply to
Maybe One Day

I think everyone has repaired 'what they thought it was' and found the real problem along the way. So paying the garage will probably get the desired result, but not necessarily by the most economic route.

Reply to
Mrcheerful

My idea is that the dealer can't see how either - but the usual method is to replace associated parts until the problem is fixed. The vacuum pump is probably easier to replace than the servo, otherwise they'd be doing it the other way round.

I'd have thought bleeding the brakes would be the cheapest thing to try first!

Reply to
Mark W

Agreed. I had a similiar problem with my VW Transporter. After I flushed and bled the brakes, they would drag after heavy braking (until I stopped and allowed then to cool). But the pedal felt higher than normal too.

I bled the brakes again, this time making sure that the pedal got released slowly as the bleeding progressed (the wife was working the pedal). I don't know if there's something special about releasing the pedal slowly, but the workshop manual for my Nissan makes a strong point about doing it that way.

That second bleeding fixed the problem.

John

Reply to
John Henderson

releasing the pedal slowly reduces the chance of it sucking back fluid or air and allows the reservoir time to top up the actual cylinder, a few second pause at the top is a good idea too.

the op problem sounds like either a stiff linkage or a faulty master cylinder with a slim chance of a servo fault (not returning) older servos had a variable length push rod which if mal adjusted could hold the brakes on, I do not know if the op car has that.

Mrcheerful

Reply to
Mrcheerful

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