Help! Brake Problem!

[railer75]

I need help with a brake problem on my 87 Vette- This is my first Corvette so I am not very familiar with it. The front brakes hang up and won't release completely- which causes the wheels and rotors to get very hot and excessive pad wear. The rear brakes operate normally. I have replaced pads,rotors, master cyl,brake lines-the system has been drained and flushed with new DOT 3. I can free up the brakes by releasing hydraulic pressure by cracking the bleeder valve,or the line at master cyl or at the abs unit. At this point I am thinking the problem is the abs-maybe a stuck solenoid? I bought a used replacement from another 87 on Ebay but when I was going to install it I foud the wiring was different! Mine has 3 harnesses/plugs but the replacement has 2. They both have the same model # -Bosch 0 265 200 020. I called the local Chevy dealer - they confirmed that there were 2 different set ups for that year, but had no other info. I could really use some advice- Thanks

 

[TWISTERUP]

If you're sure you have the correct M.C.---try loosening the MC and moving it away from the brake booster to see if that also frees up the brakes---it's possible someone may have adjusted the pushrod behind the MC trying to "correct" a low brake pedal problem--that is another possibility which could cause your problem.

 

[stang-etr96]

You didn't mention replacing or rebuilding the calipers, which sounds like are hanging up in the piston area.... ie; o-rings or corrosion in the piston cups.

 

[railer75]

C4 Brakes

Thanks to Twisterup &Stangetr96 for the response-We checked the m/c and actuator rod and the calipers are good-replaced the left one- and are now concentrating on the abs -I am looking for info on the difference/capatibilty of the 2 abs units for that year.

 

[tonylong]

BTT, just want to follow this thread for possible future needs.

 

[85c4L98]

i wud look into the brake hoses.there known to collapse internally

 

[railer75]

Found ABS to be the problem-replaced the pump and everything is OK- Thanks

 

[railer75]

I replaced the master cyl before the abs pump- did not fix - abs pump was the problem

 

[roscoethug]

Hey railer75 - Did you do anything special when replacing the modulator pump/valve assy? I'm about to do this on my '88, and it seem straight forward. Is it?

 

[railer75]

Hey railer75 - Did you do anything special when replacing the modulator pump/valve assy? I'm about to do this on my '88, and it seem straight forward. Is it?

I didnt do it myself- had it done by a local mechanic-don't think it was too hard- I remember that there wre 2 different abs pumps w same part #- one had 2 wiring harnesses- the other had 3- so you might want to check-

 

[roscoethug]

I didnt do it myself- had it done by a local mechanic-don't think it was too hard- I remember that there wre 2 different abs pumps w same part #- one had 2 wiring harnesses- the other had 3- so you might want to check-

Thanks railer. I picked up a used Valve Module/Pump from a Vette salvage yard, and installed it. Bled the brakes and problem solved. In the future when changing pads I'll open the caliper bleed valves before compressing the pistons. I think that was the issue...dirty brake fluid back fed into the ABS caused an ABS pistion to stick. In the future I would get some rubber plugs to put in the brake lines when replacing the modulator valve, and save a mess. All the brake fluid wants to run out into the ABS tub. I picked up a used "1988 Corvette Electrical Diagnosis Service Manual Supplement" at Carlisle. Best $40 I ever invested in the car. It took me through a step by step diagnosis of the ABS using only a volt/ohmmeter and pointed to the modulator valve/pump as the problem. $150 for the modulator and $40 for the manual. Much cheaper than trying to find and buy a diagnostic code reader and a rebuilt pump assembly.