Need advice: The pedal on my '71 goes to the floor on the 1st push; with about 3 pumps the pedal comes up, but not firm. It's a manual system. I've had the master cylinder replaced 3 times (1 original change and 2 warranty replacements). Each time after replacing the MC, I lost the pedal after almost exactly 3 driving miles and had to pump the pedal to stop. The garage that replaced the MCs, subsequently recommended replacing the proportional valve. Did that, no help. There is nothing else the garage wants to do, so they sent me home. When I bleed the system, I get a semi-firm pedal, but still lose it after about 3 miles. There are no fluid leaks. I've replaced 3 calipers over the last 8 months or so. The calipers don't get hot so the fluid shouldn't be breaking down. I have the original rotors (I'm the orginal owner). What equipment do I need to check the run-out. All said I'm not sure what to do next. The car really isn't drivable now.

Check the rotor runout and wheel bearing play. Either one will push the pads back into the calipers and create low pedal. If its fair then gets worse after driving, I would tend to suspect loose wheel bearings. The front can be adjusted if they are in good shape. The rear is a bit trickier. Be sure to check all of them. It only takes one loose one.

Ken Styer

Make sure you're bleeding the brakes in the proper sequence. Both the Chilton's and Haynes manuals list the sequence in the Brakes chapter (#9 I think it is).

Tools to check runout Here is an example of a dial indicator.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=623

You will also need a stand Something like this.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=5646

You will be looking for something less than .007 inch total runout. My guess with your 3 miles to low pedal you are greater then .030 range.

What about replacing all 4 rotors?

You can't go wrong replacing the rotors, but you still need to check the play in the wheel bearings.

Ken Styer

To close the loop on this thread:

Got rear rotors, front rotors and hubs from Muskegon Brake. Muskegon assembled and trued the front rotors and hubs, and checked the parallelism of the rear rotors before they sent them (a reasonable additional charge). Also replaced the front wheel bearings and seals. Everything was "bolt off, bolt on." Discovered the left rear brake (the only one not recently replaced) was bad, so called Muskegon again and got a ss sleeved calipher from them.

While the car was still up on jacks with the wheels off, I bled around the car, i.e., left rear, right rear, right front and left front, 4 times to ensure all the air was out of the system (My wife was in the cockpit working the pedal; once around would have been enough for her). Maybe overkill. But...

the pedal came up and stayed up..."no pedal" was my initial problem. See earlier posts, the "professionals" had thrown up their hands.

Only glich I encountered was that the new left rear calipher heated up when I test drove the car. Posted the problem around; replies focused on a bad rubber brake hose. Called Muskegon for a new rubber hose to the steel line (I was in no hurry). Got it, put it on and the calipher went "cool."

I'm not much of a shadetree mechanic, but got everything apart and back together (everything that came off was OEM...34 years old). A lot of grease, but no skinned knuckles. With e-posting advice from this forum and CorvetteFAQ messageboard, I was comfortable doing the job. I made Muskegon Brake my single parts source. They (I talked primarily to Justin) were easy to work with and I recommend them.

Total parts cost was about $590. My "unskilled labor" was about 6-7 hours, give or take, spread over 3 weeks or so.

Most importantly the car is drivable again.

It's a nice feeling not to have the pedal go to the floor when you step on it isn't it...!!!
____________________________________

Jim O.
Save the Wave...!!!