Rear brakes

[BigTom]

Hi guys a quick quiz for you.
I have a 1991 90 2.3 20v which has just failed its MOT. The problem is the rear brakes. When the pedal was depressed the reading was under the required value but if the pedal was held down the reading went up above the value required. Troble is, it still counts as a failure. Any ideas why and what to do about it?
Thanks for any help you can give, I really appreciate it.

[Rusty]

What value? Brake force on MOT? Has your car got ABS? Is it like a delay, need to be a bit more specific I'm afraid.

[DarrenM]

Im confused too, if the pedal held down and its over the requirement...surely thats OK then?

[BigTom]

Thanks for the replies guys and Im sorry for the confusion. Yes the car has ABS but the reason it failed is that when the pedal is first pressed it doesn't reach the required value. Its only when the pedal is held down for quite a while it rises. Apparently its the delay that failed it. I'll try and get some more info if I can asap. Thanks again guys.

[GT500]

Sounds like your "bomb" is knackered!
Try driving along and hitting the brakes hard, does it have a delay before standing on its nose?

[BigTom]

The brakes have never been great since I've had it but have always worked. I was expecting a very sharp brake pedal after reading about most Audi's but didn't get one!

[BigTom]

The brakes have never been really sharp as I was expecting from an Audi. I've always been able to stop even when faced with large roadkill! I will do the tests tomorrow and post up the results......Thanks again.

[Flat on my back]

.

You also have a brake pressure regulator for the back to consider...2wd of 4wd?

Search for brake bomb test and try that.

Try it with the abs off...if you can get onto the mot rolling road again.

[Acidburn]

don't forget 20v.org has some good info and tests on this.

[BigTom]

Well, I did the tests today and it looks like the bomb has gone off. Started the car pressed the pedal a few times. Light came straight on and pedal felt very wrong. Switched the engine off and pumped maybe once or twice before the pedal was solid.

Question is what part number do I need? I have a 2wd 1991 90 20v with ABS. I know here are two types from reading other posts and don't want to get the wrong part.

[S2central.net]

PM me your chassis number... I can't remember when the bomb changed over.

[GT500]

Do I get a beer?

[S2central.net]

Yes GT - a full crate of virtual beer Well spotted that man !

[BigTom]

Here is my number for you guys

V.I.N : WAUZZZ8AZLA214199

ENGINE NUMBER : 7AO11900

REGISTERED : 01-11-1991

Thanks again all, beer all round

[S2central.net]

OK - you have the later type... See attached PDF.

The bomb you need is Item #4 - note the VIN - 4A0 612 061 D

My advise to you for changing this is to get some other parts that are going to be extremely rusty and may be damaged on removal... Putting on the old mounts is bad practise IMO and you MUST renew any oil seals and banjo bolts.

Items 1, 2, 3, 5, 6, 7, 9 & 10 - check the quantities listed and make sure you get the right version for your bomb. Thats for Items 1, 7, 9 & 10

Pretty horrible job doing the bomb but as I say - if you use new parts to rebuild it, you will find it a bit easier - costs more money - takes less time !