968Forums.com

OK - I've got this 1992 968 I bought for parts and the car was just too nice so I've restored it to be a street car - something to beat around in that's the same year and model as my race car.

It sat for 6-8 years. I got it running well and drove around some country roads. Checked the brakes - all four rotors were hot so brakes seemed to be operational. Rotors and pads were just cruddy so I replace with new rotors and pads. Go to bleed the brakes - cannot get hardly any out of the rear calipers. Here's my symptoms:

• Can't get any fluid out of rear calipers - only a spit or two - pedal will not go down with bleeders open
• Front calipers - I can pump fluid through but it takes a mule to push that pedal
• When the front bleeds it feels erratic - pedal won't go, then will drop, next pump smooth, then pedal is rock hard won't move, next pump it'll go down but not smoothly - sorta weird
• Front calipers will function
• Rears calipers do not function with pedal depressed
What I've done:

• Bought a motive power bleeder - this did nothing alone - but it did help when I also push the pedal
• Started disconnecting the rear lines where there were fittings to see if there was fluid/blockage - no fluid at the rear fitting where the lines disappear under the chassis -
• Disconnected the lines at the master cylinder and looped hose back into the reservoir - brake pedal works nice and smooth - fluid moved from both lines no problem
I figure there's a blockage somewhere - not sure if I can run compressed air into the system without damaging anything. I was informed not to run more than 20-30 PSI into the lines.

Can I use the power bleeder to push fluid from the rear back towards the reservoir to unseat a blockage? Can I use compressed air on the disconnected line at the MC and try to blow things out - would this hurt ABS?

Is there a stock proportioning valve that might be stuck?

Any suggestions on this odd problem?


UPDATE - I was able to isolate the blockage to the ABS pump. I figure replacing that should be the fix.

Installed the new ABS pump last night - that was a tough job. Looks like fluid is coming through so it should be good. I now need to splice the wiring together and then bring it to the P shop to have the pump properly cycled with the peewee tool or whatever that is...

That job killed off the fun of working on this car for awhile...

did you install a different bias valve while you were in there?

Hi Flash - no, didn't install a new bias valve - heck not even sure where that is. Is that something I should be doing?

I did finish wiring up - that was a bit of luck - several sets of wires were duplicate matches. I spliced them and had no ABS light. Tested in the driveway - felt good. Went and road tested it last night in the rain. Hammered the brakes and the ABS worked fine. All four rotors were hot afterwards so they are clamping. Felt like brand new.

Loren at Renn suggested I have a shop use a PST2 or PIWIS tool to cylcle the ABS pump to get any air out. Not sure why - the system bled perfect and operates fine.

Do I have anything to worry about here? I may take it to a shop for a safety check but it seems to be operating fine - but safety is always first.

Any suggestions for me?

Thanks

the bias valve is what determines how much braking goes to the front versus the rear - many of us who prefer a bit more rear braking than what is provided in stock form have changed that valve - do a search here and you will find all the part numbers and discussions about it

I'm familiar with the adjustable bias in several race cars I've owned - great to have in the cabin to adjust, particularly in the rain.

I thought a bias valve might have been the source of the original problem and but I couldn't find one on any of the schematics or repair manuals I've got. I'll run the search - thanks for the tip

Brake bias valve is located under the liner on the passenger side wheel well. I've seen Pete do a number of these. Getting in there is a PITA. Most folks like the result.

Regards,

Jay