Firm brake pedal 97 A4 tdi

[gunman]

Slight problem with my new A4, just noticed this eve that some times the pedal goes solid as if there is a servo failure, a few secs later and all is well again for a while. Didn't seem to do this when I test drove it, unless I was just unlucky.

It was dark by the time I got back so will look in the morning, but do these have a vaccum pump like the 1z? If it were the servo would it not be like that all the time?

cheers.

[gunman]

OK, had another look this morning. Fault is there all the tame, basically, you get servo assist on the first push of the pedal. After that it goes solid unless there is about 15 secs between presses. If I pump the pedal with the engine off until the pedal goes solid, then keep y foot on it and start the engine it does drop but very slowly.

I pulled the vac hose off the servo and there is suction there, not sure if it's enough but it seems more than I had on the 80 when I was working at it.

I have been reading on other forums and this seems common on the B6 and is caused by the servo leaking and water getting into it but cant see any reference to the B5 having these issues.

I might try to hook up the servo to another car sitting beside it, but I'm starting to suspect the servo.

When they work as expected, the brakes on this car are about the sharpest I have ever felt.

[Monkeymagic]

Id be checking the tandem pump too, is there good vacuum from it with engine running. remove it from the bulkhead and place a thumb over it. The crimped together seals on the b5 servo can suffer and ingest water the same as the b6 and b7 if the drains below the servo and the battery are blocked.
Also pull the master cylinder forward they can corrode due to the above problem. In freezing weather it can cause all sorts of trouble. The answer really is to treat cleaning the drains as a service item...

[gunman]

Erm, what is the tandem pump?

I checked the 80 here and the vacuum is much stronger thn the A4, hooked the A4 servo tot he vacuum off the 80 and it feels a lot better, tho obviously the car cant be driven hooked up like this.

It looks now like it could be the pump as even disconnected right back to the pump provides little suction.

Anyone know if the 1z and afn pumps are the same?

[Monkeymagic]

I dont think the B5 uses a tandem pump eg it drives fuel and vacuum for servo as they have a seperate fuel pump. However they still use a camshaft driven pump to create servo assistance. It will be on the firewall side of the head with the vac pipe coming off it.

[gunman]

OK, I am a dumbass!

First off, I can confirm that the vac pump on the 1z and afn are interchangable, as I have just done it. PN was an exact match. I can also confirm that there wasn't anything wrong witht he pump on the A4 as it is perfect on the 80. I did find that there was a worn through hole on the vac pipe just after the pump tho. I found this when refitting after swapping the pumps over

Lesson learned, fully check the simple stuff properly before swapping parts!

Good news is that it seems fine now, at least on the drive anyway. I'll take if for a run shortly. That pump isnt that easy to get out, really awkward to get it at.