'87 Brake Problem
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Drifting
Joined: Feb 1999
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From: Perpetually Lost PA
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'87 Brake Problem
Got a question about an 87 that belongs to a friend of mine...
The left front brake will not bleed unless the engine is running and there is assist from the brake booster.
Car pulls to the right when braking. (DUH!)
When you can get enough brake pressure to apply the front left brake, the caliper will not release unless you open the bleeder.
Calipers, rotors, disc pads and hoses for each front brake have been replaced and the symptoms are still there.
Any ideas? Could this be the ABS unit?
TIA!!!
The left front brake will not bleed unless the engine is running and there is assist from the brake booster.
Car pulls to the right when braking. (DUH!)
When you can get enough brake pressure to apply the front left brake, the caliper will not release unless you open the bleeder.
Calipers, rotors, disc pads and hoses for each front brake have been replaced and the symptoms are still there.
Any ideas? Could this be the ABS unit?
TIA!!!
Instructor
Joined: Jun 2008
Posts: 138
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From: Bridgewater Ma.
I had a similar problem with a prior GM vehicle. Turned out to be the brake hose. They get very hard over time and restrict flow.
Is the car equiped with the original rubber brake hoses? If so I would suspect that first.
Is the car equiped with the original rubber brake hoses? If so I would suspect that first.
Team Owner
Joined: Sep 2003
Posts: 20,179
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
As previously listed, check the mechanicals first.
The ABS uses 3 channels, LF RF & Rear. It could be a fault of the ABS. You might try pulling the ABS fuse and going for a ride. Worse case senario, you'll lock 'em up when panic stopping. But the brakes will still work.
The ABS uses 3 channels, LF RF & Rear. It could be a fault of the ABS. You might try pulling the ABS fuse and going for a ride. Worse case senario, you'll lock 'em up when panic stopping. But the brakes will still work.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
It's possible that there is a restriction in the hard line from the ABS unit to where the LF hose attached to the hard line. IF the fluid in the system was old, there could have been some debris come loose during a flush.
But having the engine running shouldn't make that much of a difference if the lines are clear; I bleed my 87's brakes with the engine off and there is no problem with getting enough pressure.
The ABS modulator valve cannot raise pressure to the brake lines and the ABS should not play a part in bleeding that line with the engine running or not. Unfortunately there are no on-board diagnostics (paper clip method) for the ABS system, you have to use an ABS diagnostic tester. It could be that one of the two relays is not working properly. The ABS does a self-test when the engine is started and the car moves forward thru 3-4 MPH and is an audible buzzing sound. Do you hear that??
If you have access to a pressure bleeder, remove the hose at the hard line connection and let the pressure bleeder run a fair amount of fluid through that line. If the fluid comes out clear and the problem still exists, I would suspect a bad modulator valve in the ABS. That valve is not serviceable so the repair is a replacement of the ABS pump.
But having the engine running shouldn't make that much of a difference if the lines are clear; I bleed my 87's brakes with the engine off and there is no problem with getting enough pressure.
The ABS modulator valve cannot raise pressure to the brake lines and the ABS should not play a part in bleeding that line with the engine running or not. Unfortunately there are no on-board diagnostics (paper clip method) for the ABS system, you have to use an ABS diagnostic tester. It could be that one of the two relays is not working properly. The ABS does a self-test when the engine is started and the car moves forward thru 3-4 MPH and is an audible buzzing sound. Do you hear that??
If you have access to a pressure bleeder, remove the hose at the hard line connection and let the pressure bleeder run a fair amount of fluid through that line. If the fluid comes out clear and the problem still exists, I would suspect a bad modulator valve in the ABS. That valve is not serviceable so the repair is a replacement of the ABS pump.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Got a question about an 87 that belongs to a friend of mine...
The left front brake will not bleed unless the engine is running and there is assist from the brake booster.
Car pulls to the right when braking. (DUH!)
When you can get enough brake pressure to apply the front left brake, the caliper will not release unless you open the bleeder.
Calipers, rotors, disc pads and hoses for each front brake have been replaced and the symptoms are still there.
Any ideas? Could this be the ABS unit?
TIA!!!
The left front brake will not bleed unless the engine is running and there is assist from the brake booster.
Car pulls to the right when braking. (DUH!)
When you can get enough brake pressure to apply the front left brake, the caliper will not release unless you open the bleeder.
Calipers, rotors, disc pads and hoses for each front brake have been replaced and the symptoms are still there.
Any ideas? Could this be the ABS unit?
TIA!!!
We just had another bad ABS unit last week.
http://forums.corvetteforum.com/c4-t...releasing.html
Last edited by pcolt94; Jun 22, 2009 at 03:58 PM.
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Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Pulling the ABS fuse effectively bypasses the ABS system. And unless the ABS activates, normal braking effort doesn't use the ABS.
Do a flush of that line first to see if the problem clears up. You may have to pass 3-4 ounces of fluid through under pressure to flush out any gunk.
Did you buy new calipers or rebuilds? Sometimes rebuilds will not be really clean or the pistons may be causing the problem by not sitting in the bores properly or a rough surface in the bore or the piston wall. Actually after thinking about that, I'll bet the problem is in the caliper.
Might be worth pulling that caliper and taking the piston out and flush out the fluid and clean everything up then inspect it carefully. You should be able to get new seals to re-assemble the caliper. Start there before playing with the ABS too much.
Do a flush of that line first to see if the problem clears up. You may have to pass 3-4 ounces of fluid through under pressure to flush out any gunk.
Did you buy new calipers or rebuilds? Sometimes rebuilds will not be really clean or the pistons may be causing the problem by not sitting in the bores properly or a rough surface in the bore or the piston wall. Actually after thinking about that, I'll bet the problem is in the caliper.
Might be worth pulling that caliper and taking the piston out and flush out the fluid and clean everything up then inspect it carefully. You should be able to get new seals to re-assemble the caliper. Start there before playing with the ABS too much.
