Brake Hydralics - HELP!!!

[benspeed]

Thanks guys - really appreciate the help. This is the barn find and will just be a street car.

Looked over the rubber hose sections in the back and they don't seem collapsed - also opened up a fitting before the rubber hose - no fluid.

Tracked the lines and don't see anything crushed.

The mystery to me is this is a closed system so what could get in there and stop it up? Congealed brake fluind?

Figure I'll take the line off the master cylinder and off the back of the calipers and try some compressed air from the master cylinder side. Would that damage ABS? I want to leave that working.

I don't know where to hunt for a stock proportioning valve - that's been on my mind - some kind of valve being stuck. Where would I look for that? I haven't been up underneath the front yet - been working my way from the back to the front.


Got a total of $2200 into this car now - magnetic numbers are just for fun.

Thanks again for any suggestions.

[Spinnetti]

um, if you think about it a bit, the rubber line idea is not plausible. Does the car have a distribution block? some cars have an automatic prop valve/distribution block on the firewall, which also cross biases the brakes. Sounds like a stopped up plunger preventing both rears from working. Your rear pistons might be seized which could explain both symptoms in the rear of not bleeding and not working. If you power bleed it, and the rears will bleed out but still won't move, then likely your rear calipers are seized. Do you have a repair manual? It should cover all that stuff...

[pfcs]

Most late model MB and Audi with stability control/ABS systems will not manually bleed. They require flushing with a (relatively) high pressure pressure bleeder (2-3 bar/30-45psi) with system enabled (ign on) The appropriate tool is $1200 and has an electric pump. One of the BMW tuners (Turner Motorsport?) sells a nice hand-pump pressure blleder tank w/resevoir adapter for around 80bucks that works well-just need to keep it pumped up enough. phil

[benspeed]

Caplipers aren't seized - the pistons move no problem.

I'm leaning towards a clogged up ABS pump - one Porsche expert suggested that enough moisture may have seeped in while the car was sitting that the ABS pump got corroded. I believe that's up behind the passenger fender - going to pull that off and see if I can get any fluid before the pump. That would also explain why the fronts barely bleed.

I have the factory manual - not the greatest - I was suprised how little it had on the braking system.

[924Guy]

Yikes... sucks/wierd that you'd have to have the ign on to bleed - all our Bosch systems (at least for sure 5.X-onward) are all flow-through - can bleed with ignition off.

If you pull the rear lines off after the ABS unit and see about blowing air through there, you should be safe and also isolate any issues that might occur with the ABS unit; it should be safe against sticking, but hey, who knows...

[benspeed]

Must have said something wrong - don't need the ignition on to bleed although I tried both off and on. Didn't make a difference.

Thanks Vaughan - will let you know how this turns out - likely will post more info for help!

[pfcs]

Ben-if it's the late German syndrome, you need to force the fluid thru with the hi pressure type bleeder, not pump it thru w/pedal. If it's this case, you will not be able to get a decent peadal no matter how long you pump the pedal! phil

[Spinnetti]

Ah, I forgot about ABS... Used to my old cars Yep, there's a special procedure for that, and IIRC, it does require a pressure bleeder (I don't have it handy, but have it somewhere on my Audi service DVD somewhere)