abs rearbrake problems (copied from engine section)

[Redfox 10]

Hi all,

Helping a friends 2L.16V 1993 ...P...) out, abs brakes but no eds. Been swapping the pressure regulator valve in front of the abs unit out (the one for the rear brakes. Also swapped the hydraulic pump (motor) and the pressure accumulator, but to no solving. The problem is, that it couldnt brake on the rears first. Then it developed a nonexsistent brake servo help, as the electric engine took off. Then we changed the aforementioned parts, and we have again an engine that spins, and brakes the front brakes, but won't let out any pressure to the rear brakes.

Followed the ideas mentioned in the Bentley manual, but didn't sort it completely.

Any ideas?

 

Cheers,

Redfox.

 

edit: eds - electronic differential system.

[floppyman 0]

Is there oil pressure from the abs pump for the rear brakes? If you dont have pressure on the rear calipers but have pressure in the pump I would say the rear brake bias valve is gone

[24V Renshaw 0]

Yep everything points to the bias valve...

[Redfox 10]

When you say bias valve, is that what is described as the pressure regulator valve, numer 5, in the Bentley manual on page 45,4?

If it is, then I have already changed it for another one. Part no. 191 614 163 A.

 

Or do you mean the valve which sits close to the rearaxle?

If so, then I have taken off the feeding brake line, and it was only dripping out veeeeery slowly.

I have followed the procedures for changing brake fluid as per Bentley manual.

Nothing comes out at all.

 

Cheers,

Redfox.

Edited December 5, 2011 by Redfox

[Supercharged 2]

The valve near the axle...

 

Any fault codes?

[Redfox 10]

I cannot look for it, as I don't have any device.

 

Cheers,

Redfox.

[davidwort 0]

don't think uk 16v had eds, only on the VR6.

does it have a 357 or 535 part number on the abs unit, 535 is non-edl

 

ah, sorry, read the edl wasn't working :) you meant it's the non-edl spec...

 

 

not the bias valve then by the rear axle, feed lines should **** out fluid when you disconnect them, must be abs unit valving then.

Edited December 5, 2011 by davidwort

[floppyman 0]

How did you bleed the brakes? Did you use a pressure bleeder? When replacing abs units it can be a pain to bleed.

[Redfox 10]

No, I did not use a pressure bleeder. the old two man job. Works a treat on my own car (also abs, non edl).

So, we just changed the whole front of the abs unit, plus the abs valve block too. Same problem. Must be an electrical problem, either by a bad ground, or the control unit (under the left side rear seat?) or something else?

The only thing we have not changed now (in the engine compartment) is the rearmost part of the whole abs unit.

 

Since I don't have a VW dianogstics computer, it's pretty hard to move further. Any ideas?

 

I have been thinking a little aboout it, and as I see it, it could go like this:

let's say the pressure pump went dead. I know this for sure, since I physically took it off, gave it some power and it did not spin, and the new pump did. But now we assume, that the pressure pump is still on and not touched, jsut dead.

Then the ABS control unit see this and priorytates this as a severe ABS failure.

This then shuts off the ABS function.

That is why after we changed to a new electric pressure pump yesterday, could have brake pressure, but not all over, and it locked the front wheels.

The ABS computer keeps this errorcode as it is an eprom, so even as we took off the battery of the car, it still keeps the errorcodes, thereby still see a "dangerous" ABS error, and do not turn on the ABS function.

That in turn means as long as the VAG 1551 or whatever computer have not read out the errors, and they are being deleted in the ABS computer, then the error will not go away, because the car see it as if the ABS error is still there, even though the error is physically repaired.

So, what can be done, is to connect a computer to read out the error codes, and delete them. then take aspin in the car, and see:

1/ if the ABS will work on the front wheels, by braking hard.

2/ if this also happens on the rear wheels.

3/ if the brakes then actually work on the rear wheels, thereby allowing fluid to pass through in a bleeding process.

4/ if the abs lamp makes anormal behaviour, like blinking, slow, fast, long etc.

 

Am I correct is this?

 

Cheers,

Redfox.

[floppyman 0]

It doesnt matter if the pump works or not. You would still have good working brakes all around. Bleeding brakes with the brake pedal is a big no no, but anyway. Where are you located? Maybe some one near you with vagcom to check for errors.

I think you got to different problems, one of the rear brakes and the other with a fault with the abs system that makes the light go on