04-24-2009, 02:06 PM
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.
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.
(This post was last modified: 04-25-2009, 08:29 AM by benspeeder.)
