brake pedal came back up, heard werid noise?

[tigmaned]

i am thinking air in the line or really bad brake fuild, since what i can see is really dark. other day while idleing in a parking lot had my foot on brake and by its self it move up and down some. and today i had my foot on the brake and it all of a sudden came back up against me and i heard a funny moan like sound under the car just in front of my feet. i am think the brake control valve that sends each line to each brake is under there right? but both times it happen at a long idle which hasn't been that great and maybe low vacuum was the cause too?
could i have a bad vacuum check valve going to the booster?

 

[86PACER]

Is your ABS light staying on?

 

[tigmaned]

when i start the vette the abs is lit, then goes out and i am not sure when but comes back on, so yes the abs light is on. BUT i thought the ABS system didn't effect the normal brake funtion at all??

 

[86PACER]

The light should not be coming back on after it turns off when you start the car. You got a problem in the ABS system.
When you start the car, and roll up to 4MPH with your foot on the brake pedal, you should hear the ABS Pump/Modulator Valve prime, and feel the brake pedal pulsate at the same time. This is the ABS auto check. Are you sure the sound you heard was not from behind the driver's seat?
The brake system would still work fine even in the event the ABS has a problem, just ABS won't work. But the ABS Pump/Modulator Valve can transmit through the brake pedal when it's keeping the brakes from locking up by controling brake pressure. In your case it sounds like the ABS kicked in when it was not supposed to. The ABS Pump/Modulator valve is located under the storage comparment behind the driver's seat. I would do some simple troubleshooting. A GM Shop Manual would be very helpful in checking that you have the right voltages at the right times in the right wires.

For starters, check the INJ 1 Fuse, Brake Fuse, Guages fuse, and the Sop-Hazard fuse.

http://corvettefever.com/howto/19239/
http://automobiletest.com/service/1987corvette/abs.htm

If you end up finding a bad relay, I got extra ones.

 

[tigmaned]

when i first got my vette about 7 months ago, the ABS light was on. i trouble shot it and found one of the relays didn't work. i changed it then and the light hasn't come on till about 2 weeks ago. i didn't care since i only drive her in sunny times if i can. but this grown sound i heard when the pedal came pushing back against my foot it was in front of me and why i am wondering control valve or booster? but i can't say i hear a vac leak from the booster and its not hard to push the pedal in??
thanks for your help!!!

 

[Jeb]

That groaning sound you are hearing sounds just like when the ABS does its autocheck when you are first moving after starting the car. You'll also feel some pulsating in the pedal when this occurs.

 

[tigmaned]

but wouldn't that sound be behind me, thats were the ABS is. next wram day i have to flush all the brake fuild out i think thats a little of the problem too.