Classic Audi Technical Mech/Tech Suspension & Brakes » B4 brakes

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Old 08-12-17, 09:20 PM   #1
rangerovering
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Default B4 brakes

Hi

Problem with the 80s rear brakes, cant get any fluid to come through on the NS, even with the caliper off the pedal still is firm like there is a closed circuit.

I get fluid coming up to the ABS block if I crack each Union for the feed pipes, but nothing coming out the top.

Thought it was the brake compensator valve when I found one of the plungers was seized but having freed it off, still no joy.

Can anyone help?

Thanks


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Old 08-12-17, 10:18 PM   #2
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Sometimes running the engine, allows fluid to flow through the ABS block.

Not familiar with that car setup. Do you have 2 pipes running front to back for the rear brakes or do you have a split at the rear like earlier cars ?
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Old 08-12-17, 10:34 PM   #3
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Yes 2 pipes going to the rear mike, I did run the engine briefly but you think maybe running it longer would work?


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Old 08-12-17, 11:04 PM   #4
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I always bleed the brakes on these cars with the engine running as I've had problems with no fluid getting through which I blamed (rightly or wrongly) on the stupid pump/bomb based servo system, its always worked for me when I have it running, without it running I find it extremely difficult to get fluid through the system, have you tried to undo the union at the compensator valve to see if fluid is there ?

However are you saying the ABS unit is not allowing fluid through as I've never come across that before, could it be a stuck valve in the ABS unit ?
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Old 08-12-17, 11:51 PM   #5
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must be a 4 channel ABS unit then if you have 2 pipes going rearwards.

As Dave says, never seen any problems with them. I'd try running the engine while trying to bleed it. Are you using a bleeder tool or using the old pump the pedal method ?
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Old 09-12-17, 12:01 AM   #6
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Pump the pedal method usually works better than bleeder tool (be that a push with air pressure or a vacuum pull tool) bit daft but have to ask you have you checked that the master cylinder is actually pushing fluid through both circuits as could be faulty on one of them ?

In fact have you bled the master cylinder if its got a bleed valve, you would need to do this if fluid went too low and a chamber emptied.

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Old 08-12-17, 11:58 PM   #7
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Hi Dave,

Ok that’s helpful I’ll need to try with it running 👍

I undid one side on the compensator (the OS line) which was weeping a fair amount of fluid. The NS line didn’t weep very much at all.

When I undid the unions on top of the ABS pump both ports looked fairly dry, pressing the pedal didn’t push any fluid out.

Suppose it could be the ABS unit at fault, is there much can be done to investigate?

Cheers


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Old 09-12-17, 12:16 AM   #8
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Yep I cracked each inlet circuit Union to the abs unit in turn, both squeezed out fluid when I pressed the pedal.

There is a bleed nipple on the MC yes. It seems to be isolated to the rear NS, the front brakes are ok on the MOT balance check and the rear OS seems to be working to some degree although I’m not saying it’s perfect either


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Old 09-12-17, 12:46 PM   #9
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Reference pumping the fluid by hand/ foot, i wouldn't as has already been highlighted your reservoir could run dry and more importantly doing it manually has in the past ruined a few peoples master cylinders due to damaging internal seals. If i were you i'd get one of these they're brilliant much better than a Gunsons. Just don't make the mistake i made and forget to really tighten up the filler cap or you won't get pressure build up.

http://www.ebay.co.uk/itm/Sealey-VS8...EAAOSw6WdXiScF
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Old 10-12-17, 05:49 PM   #10
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Thanks VDT I might be needing to buy one of them, still no luck tonight with the ending running just doesn’t bleed through at all.

Had the vcds plugged in, no fault codes on the ABS but intermittently the ABS light on the dash would come on and go out..... don’t seem to be able to force a power up of the module on this car to aid bleeding as far as I can tell either.

I’m just a bit unsure if the pressure bleeder will still force fluid through? And whether the brakes will actually work once they are bled?


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