Spongy brakes after replacing brake reservoir....help!!

[skree25]

Last week I replaced by brake reservoir in my 1999 Audi A4 Avant which literally crumbled into pieces in my hand. Now however my brakes are only about half of what they used to be. They work well enough to drive around on but are very spongy and have almost no grab over the first 50% of brake pedal travel.

First thing I did was bleed the brakes, several times. Used a vacuum bleeder to no avail. Then I read a few posts about air getting trapped in the ABS so I tried to run the VCDS ABS bleed procedure but all I get is an indefinite beeping and flashing ABS light but no noise/pumping out of the ABS unit. My VCDS performs most other functions for my B5 correctly but can't seem to connect to/communicate with the ABS unit.

Am I right to assume this is probably related to air in ABS or should I be looking at something else like brake booster or master cylinder? If it is ABS and I can't connect to the ABS controller via VCDS, can I drive around on the ice a bit to manually pump the system or do I need to suck it up and get a new ABS unit?

Any ideas???

[MetalMan]

Could be air in the ABS module. With VCDS after it connects to the ABS module, you go to "Output Tests" and it will cycle through each wheel.

You may need a pressure bleeder to get all the air out if any made it's way into the master cylinder.

[Tanzimur]

Could be air in the ABS module. With VCDS after it connects to the ABS module, you go to "Output Tests" and it will cycle through each wheel.

You may need a pressure bleeder to get all the air out if any made it's way into the master cylinder.

what he said! and if that doesnt help more then likly you have to pretty much use the bleed a caliper procedure on the master as if you were bleeding a caliper. lots of air in the lines especially replacing the resv.

[walky_talky20]

Yes, locking the wheels while driving to engage the ABS pump can help to get stuck air out of the ABS block. Do that a few times, then bleed again.

I replaced my brake reservoir (during 5MT swap) and had the same problem as you. The brakes were spongy. I bled it several times and was able to do the VCDS ABS test to run the pump. This helped, but it was not perfect. I dealt with slightly spongy pedal for some time. May have got a little better on it's own. Then I replaced both front brake calipers (for rust reasons) and have replaced the front pads a few times. In particular I think the pad replacement is helpful. Specifically, squeezing the front caliper pistons back in basically does a "reverse bleed". It shoves fluid (and potentially air) backwards through the line, through the ABS unit and back into the reservoir. Air bubbles like to go up, not down, so I think doing this is helpful. My pedal feels really good now. Very close to the top, very sensitive, and not much travel.

So if you've tried everything else, I would pull the calipers off the brackets one at a time, maybe pump the piston out to fairly full extent (not too far!), then squeeze it back in all the way. With any luck, this will chase the air back up into the reservoir. While I was dealing with my spongy pedal, I actually bought a "Phoenix Systems Reverse Bleed Tool", but I never actually used it. It seems to me that compressing the pistons (and maybe time itself) did almost the same thing.

[nynoah]

You need something like this and VCDS (rosstech VAGCOM) https://www.ecstuning.com/ES2765516/...1YgaAnle8P8HAQ