I have been reading post after post regarding brake issues but have found no magic Bullitt. I have a 1979 L48. Lost brakes after a 250 mile trip to the beach. Mechanic there replaced the two back calipers. Drove it home a few days later and upon arriving I had no brakes. Pedal to the floor. Took it to a local mechanic and he replaced the lr caliper. Within a couple of days NO brakes again. Took it to another local mechanic he replaced the rr caliper. Now have replaced all 4 calipers the master cyl. and the booster. The mechanic says the car stops but has virtually no travel. Pedal goes almost to the floor. Mechanic says no air in lines. He says he can think of nothing else to do. I know it ain't right. What would you guys do next??

 

Did any of them measure the rotor runout?

Are you using DOT 5 fluid (which is likely not compatible with recently rebuilt calipers)?

 

I agree you have a run-out problem.
Here's how to check and correct run-out:


https://www.youtube.com/watch?v=SSxC...ature=youtu.be

 

Do you know how to bleed the brakes?
If not find a shop that works on older Corvettes.

 

Thanks for the replies gents. mechanic said he guarantees no air. bled in proper sequence. bench bled mcyl. The pedal is better does not go all the way to floor board and stops as it should. maybe I am chasing ghosts. have probably 1" or so when pedal is depressed. seems like the pedal was much harder prior to issues.

 

How old are the rubber hoses?

 

Using DOT 5, or 3 or 4, won't have any of the characteristics described. The notion of incompatibility has to do with longevity of the materials to resist leaking, it doesn't have any bearing on whether it bleeds well, will stop the car, or will maintain performance over several days.

 

So it seems the rear calipers have been replaced twice with this problem. What reasons were given?
You said all 4 have been replaced but your text indicates the rears only.
Is the fluid in the master dropping with each problem such that it needs to be refilled - like it's losing fluid between fixes?
When the booster and/or master cylinder were replaced, was the actuating rod adjusted for length? If too short to match the piston depth of the master, you'd have long pedal travel before the master c. piston is actuated and could run out of pedal before enough piston pressure is applied.

I suggest you make sure the system is full, jack it up and remove all wheels, crawl under the car while someone is applying the brakes very hard, and look at every line joint and caliper for leaks - from the master cylinder to the pads on each wheel. That will eliminate leaks.

Check the booster rod length - there's a gauging tool available to do this.

If everything above checks out, make sure the bleeder screws are in good condition and tightened appropriately after each bleed.

That's all I got! Good luck.

 

Fair enough. But the warning against using DOT 5 is still legitimate, especially if new calipers/MCs are being thrown around. If the OP finds a solution that works, he won't want to do it all again in a few years.

My money is on rotor runout, which can pump air into the brake calipers, especially if using the OEM-style lip-seals. Here's what I bought to check mine. The shims in the video above are still the best way to fix it, if you want to preserve rotor thickness.

 

Most likely culprit is excessive runout in the rotors. (Anything over .002”) Mechanics who are not experienced with Corvettes wont think of this but its a very common problem, and sounds exactly like what you are experiencing.

 

Can you see any leaks? Is it manual or power brakes? You say your pedal is going to the floor so you are either loosing a lot of fluid out of the rear of the master cylinder into the fire wall or booster or its leaking out of the front and rear calipers.

What everyone that is claiming runout means is that your rotors are warped just enough to cause the pads to flutter which could pump air into the calipers due to the old lip seal style. The best solution is to rebuil the calipers with o ring seals or buy calipers that are already converted. CSSBinc has an EBAY store and sells them for $480 for the complete set or about $200 for a conversion rebuild kit.

Either way your describing a low fluid or air in the system issue.

 

I quickly scanned the posts and I agree with the rotor runout culprit.

What no one mentions is that if mechanic 1,2, and 3, indeed,did remove all the air from the brake system with each caliper replacement, too much rotor wobble (runout) will pump the caliper piston seals eventually allowing air to reenter the system and the pedal to the floor issue..aka no brakes. O ring brake calipers, instead of the OEM lip seal calipers, will mask the rotor runout problem on some cars but cannot and will not fix cars with major rotor runout issues.

My OEM Lip seal SS calipers are from 1985 and still working perfectly on my car since I replaced them back 35 years ago....so much for the O ring calipers.

Fix the rotor runout and change the brake fluid every 3-5 years...you will be less likely to have brake issues

 

I wonder if the mechanic noticed there are four bleeders at the rear?

 

May well be run out. Did I mention that the rotors were replaces maybe 1000 miles or so ago. Rubber hoses are new. The correct booster from auto parts place does not have an adjustable rod. I asked the mechanic about that. My GTO had an adjustable rod. Only loss of fluid was on rear tires when those calipers were replaced. I don't THINK the calipers on the 79 have but one bleed valve on rears. Anyway, I have the car back now, car stops fine but still only have an inch or so of pedal when brakes are depressed. Still seems soft.
Thanks again guys.

 

I would bet they are not bleeding the brakes properly and just replacing parts. Get, or make, a pressure bleeder. Hopefully you can do it yourself because your mechanics don't know what the heck they're doing.

 

All C3 Corvettes have two bleed screws on the top end of the caliper one on each half of the caliper.
Try gravity bleeding the calipers.

 

You didn't mention the rotors before.

Did they get riveted back on and turned (quick and dirty way to ensure zero runout, but at the cost of rotor thickness)? Did they get shimmed properly, with screws holding them in place on the hub (the better @GTR1999 method)? If no to both, you'll really want to measure them.

There are several rotor runout tools at Amazon (click for link) that include the Vise-Grips and dial indicator. And then you'll know, and have a cool tool.

Pick up a Motive Power Bleeder, and a better clamp, and do the bleeding yourself. Your rear calipers absolutely have two bleed screws, or else they've been repaired or installed incorrectly. Here's my setup, using only air pressure. I had to refill the reservoir a bunch, but there was little mess doing it this way. On the rears, I had two catch-cans and did both sides of the caliper at once.

 

Thank you Mr. Bike space. Gonna get the bleeder. The original Rotors were removed maybe 1500 mles or so ago. No prob;lems in between then and recent issues.
Mike

 

I hope that was helpful! I'd still check the rotor runout, though.

The other tip I have for bleeding is to tap the junctions and calipers with a wrench, to dislodge the last of the air.

Let us know how it goes!