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Brakes on 82 keep airing up

Posted: 6/6/07 4:41pmMessage 1 of 14

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edingerb

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Waco, TX - USA

Joined: 6/6/2007

Posts: 14

Vette(s): 1982 Coupe; Black;

I can't seem to keep a hard brake pedal on my 82 vette. I bleed them and they are rocl solid for a few minutes to a few hours. As soon as I start driving, the brake pedal starts losing its firmness and after awhile (especially on the highway) the pedal goes to the floor and I have to pump it to get any brakes. My rotors look good and I have new pads all the way around. They are not leaking fluid. I'm stumped! Can someone help?

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Brakes on 82 keep airing up

Posted: 6/6/07 8:06pmMessage 2 of 14

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Adams' Apple

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Duncanville, TX - USA

Joined: 11/8/2003

Posts: 22720

Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

While the rotors may look good, have you checked the run-out on them?
If the rotors are warped, or running crooked, it causes the pistons in the brake calipers to "pump" air into the brake system, causing a low pedal. If they are bad enough, you could have a solid pedal in the driveway, but loose it before getting to the end of the block.
If you see no leaks, and the pedal is firm until you drive it, then I would have to suspect the rotors being warped. It may only be one of them warped/crooked, too, not necessarily all four.

Joel Adams
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Brakes on 82 keep airing up

Posted: 6/6/07 8:36pmMessage 3 of 14

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ranger3

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North Charleston, SC - USA

Joined: 3/20/2004

Posts: 4208

Vette(s): 1975 L48 AT AC T-top

Definitely need to get a dial indicator and check the runout of the rotors. It certainly sounds symptomatic of a pumping caliper piston.

Scott

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Brakes on 82 keep airing up

Posted: 6/7/07 6:52pmMessage 4 of 14

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eddie20875

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Lanoka Harbor, NJ - USA

Joined: 12/21/2006

Posts: 2191

Vette(s): 1975 metallic blue coupe with t-tops,L48, t/t steering, black leather interior. 1990 L98, white/red leather interior, auto,a/c

wouldn't a bad master cylinder show the same signs?

LIFETIME MEMBER #97
THE DYNAMIC DUO

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Brakes on 82 keep airing up

Posted: 6/7/07 6:59pmMessage 5 of 14

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Adams' Apple

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Duncanville, TX - USA

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[QUOTE=eddie20875] wouldn't a bad master cylinder show the same signs?
[/QUOTE]

A very valid question, but..No...He says the pedal is fine until he drives it. If the master was bad/leaking internally, it wouldn't matter if the wheels were turning or not...it would "leak" regardless.

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Brakes on 82 keep airing up

Posted: 6/7/07 7:33pmMessage 6 of 14

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eddie20875

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Lanoka Harbor, NJ - USA

Joined: 12/21/2006

Posts: 2191

Vette(s): 1975 metallic blue coupe with t-tops,L48, t/t steering, black leather interior. 1990 L98, white/red leather interior, auto,a/c

the way i read it was "even if it sat for a few minutes or a few hours. then if i started driving it...." i was under the impression that he didn't have to drive it for the pedal to soften. Smile

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Brakes on 82 keep airing up

Posted: 6/7/07 7:51pmMessage 7 of 14

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Adams' Apple

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Perhaps he can clarify it. I can see it could be read either way. He's working out of town at the time, so maybe when he gets back on-line, he'll post a little more info.

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Brakes on 82 keep airing up

Posted: 6/7/07 8:18pmMessage 8 of 14

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jayare

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Joined: 1/4/2007

Posts: 475

You guys are amazing.

I'm having a little of that problem. I have checked everything (in the driveway) and can't seem to get a "good" pedal. Time to check run-out.

Thanks guys......Rich

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Brakes on 82 keep airing up

Posted: 6/8/07 8:28amMessage 9 of 14

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sfindlan

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Badin Lake, NC - USA

Joined: 4/21/2004

Posts: 127

Vette(s): 1979 Red L-48 Corvette with Doeskin interior, 3-speed automatic, 3.55 rear; 1986 L-98 Coupe, 4+3 Manual - Satin Black and Purple (SCCA TT/Hillclimb Car); 1993 White LT-1 Coupe, Black Interior, 6-speed

Interesting. I have a somewhat similar problem except I will have good brakes the first time I hit them, then they are gone the second time I brake if it is within 0-15 seconds or so. Very troublesome on winding tight roads. I have new pads, new master cylinder and no leaks in the calipers. Runout doesn't seem to be a problem - as the brakes are there initially even if you drive miles. If I press on the pedal in the driveway it will slowly (very slowly) go towards the floor, although it doesn't go all the way. That is why I changed the master cylinder - as I was convinced it would be bad.

Can the proportioning valve cause the pedal to go soft like that?

C3: 1979 Corvette Coupe, Auto, L-48, Red/Doeskin (my wife's fave);

C4s: 1986 C4 coupe (SCCA road race car), satin black, 4+3, Z51 package, L-98; & 1993 C4 coupe, white, 6-speed, LT-1.

http://www.C3VR.com/member_uploads/6001_6100/6032/P102018120111222163715r.jpg

http://www.c4vetteregistry.com/member_uploads/14301_14400/14327/WolfRidge-Dusk-by-GRM20111222173029r.jpg

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Brakes on 82 keep airing up

Posted: 6/8/07 3:14pmMessage 10 of 14

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johnu

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Scottsdale, AZ - USA

Joined: 5/23/2007

Posts: 617

Vette(s): 1981 Corvette Two-Tone Claret color, 4 spd, C7 Vert

My rear rotor had a "slight" runout issue that caused the pad to emit a chirp on the first touch of the brake. An immediate second touch was quiet. A yearly bleeding was required to remove the air the pumping action contributed and tame the chirp until I had the rear bearing replaced (previous mechanics bubba according to my expert) and the rotor turned straight again.

Only 34 years together

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Brakes on 82 keep airing up

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Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

Brakes on 82 keep airing up

in Forum: C3 Engines, Driveline and Handling