A4 spongy brake pedal

[nuno.bett]

Hi,

I do have the same issue with my 1996 B5 1.8T. The circuit has been bleed, the MBS has been swapped but the spongy brake pedal is still there, only getting firmer after 2 or 3 presses. Is it possible that the ABS module isn't sealing something correctly?

Can anyone help me with a list of steps that should be done in order to locate the problem?

Best regards,

Nuno

[BrandonA4]

Has the break fluid been completely changed? The MBS has been swapped?? i presume from a wreckers it might be worn also.

[bvisser]

H Nunoi,
I know you don't want to take chances with brakes, but it seems to be normal/ok to bee spongy. The ABS works, and the brakes are as effective as any std car I've driven. Iv'e flushed all the fluid and it had little/no effect.
What you describe sounds like normal brake behavior: From the moment you last pressed the brake, the pads slowly start to move away from the disk (vibration ect) and you then have to press the peddle a few times (more than 1) before the peddle becomes firmer. As the pads first have move towards disk before it can start applying pressure. BUT, the first press should still give you good braking although the peddle travel is allot more than the follow presses?

Hope this helps, if not ignore it all

[nuno.bett]

I know you don't want to take chances with brakes, but it seems to be normal/ok to bee spongy.

Exactly, people have told me the exact same thing. When I bought the car it had the same behaviour and I've not had the opportunity to drive an exact same model to compare it with.

The ABS works, and the brakes are as effective as any std car I've driven. Iv'e flushed all the fluid and it had little/no effect.

The same here.

From the moment you last pressed the brake, the pads slowly start to move away from the disk (vibration ect) and you then have to press the peddle a few times (more than 1) before the peddle becomes firmer. As the pads first have move towards disk before it can start applying pressure. BUT, the first press should still give you good braking although the peddle travel is allot more than the follow presses?

First press gives good braking, but following presses give even more. But this can be misleading, as the car as also decreases speed and the perception of stopping power has been altered.

I also did a previous test which was starting up the car for a few seconds and then turning it off and pressing the brake several times. It allows to shorter travel every time, but I can press it 3 times before being completely stiff.

After that and while pressing the pedal, I started the car on again, and the pedal immediately depresses completely.

This morning forget to do the same test in order to check if vaccum had been lost overnight.

I also did some more research, I got to a point where it is possible for the abs pump to trap air inside, which can only be bleed while doing an ABS cycle (turning it on and off). For that VAGCOM or similar is necessary. I will ask my mechanic to try this, but before that I would like to try a different approach.

Is it possible to bypass (oily speaking) the abs pump completely (just for testing purposes, wouldn't want that for regular driving)? I was thinking of connecting the lines/hoses from Master cylinder to lines/hoses from ABS pump to Calipers with an Y connection. Anyone knows the thread size of those lines for points A,B,C,D,E,F,G I suppose they are all the same?

Here are some quick schematics, sorry for the drawing & pic quality. Cheap mobile camera.

[bvisser]

It sound to me like your brakes work as normal. Bypassing the ABS as you suggest seems to be allot of work for little gain. As they say, don't scratch it if it doesn't itch

I don't know what it will cost, but can't you take it to a road worthy test center and ask them to test your brakes / abs working on the rollers?

My simple test was to go to a gravel road and slam the brakes to check that the abs releases(and re-apply) all the brakes to all 4 wheels. Then I drove on the shoulder of a road with 2 wheel on the gravel and 2 on the tar and slam the brakes to check that the abs kicks in on those wheel and then the same with the other two wheels on the gravel (you need a quiet road for this). You have drive above (30km or something in that order ) for the abs to work, but no need for high speeds. After I did these simple test I was convinced that the ABS unit works and just made peace with the spongy feeling.

Googluck