Hello everyone,
I have a brake problem and need some help. The car is a 1972 Vette. It had been sitting for several years when I bought it. I have rebuilt the engine and trans and I am now working on the brakes. I have rebuilt all four calipers, replaced all of the soft lines, and replaced the master cylinder. I have bled the brakes manually and with a vacuum pump until fresh clean fluid comes out of the bleeders. I have checked for leaking fluid and found none. After all of this, I still have no brakes. When I press the pedal, it feels soft and the "BRAKE" light on the dash comes on. With the rear end on jackstands and the car in gear, I can press the brake pedal and get very little braking. It does try to stop the rotors but that is all it does "try".
What have I missed here? What have I done wrong and what should I look for or do next? Any suggestions would be greatly appreciated.

Mike

 

A few ideas:

Did you bench bleed the replacement master cylinder before you installed it?

Did you remember to bleed the inner bleeders on the calipers?

Did you replace the power brake booster? If so, did you adjust the master cylinder actuating rod?

Hope there's something here that helps.

 

Sounds like my story exactly. I tried to save the money and rebuild the calipers myself, but it just didn't work. I bought factory rebuilt ones and now she stops easily.

 

Thanks for the replies. I did not "bench bleed" the master cylinder. The service manual does not mention this at all. Could you tell me how to do that? On my calipers , there is only one bleeder valve so, I do not what you mean by bleeding the inner bleeder. I did not change the booster and did not touch the adjustment of the rod.

Thanks,

Mike

 

Bench Bleeding
- The master cylinder needs to be removed from the Corvette.
- Get a set of old brake lines, or rig something with flexible tubing, and route from the brake line ports back into the master cylinder's reservior.
- A local auto parts store may be able to sell you a kit for bench bleeding. Most master cylinders come with plastic fittings and flexible tubing for doing this procedure.
- Mount the master cylinder in a vise on a sturdy bench.
- Partially fill the reserviors with brake fluid.
- Slowly press the piston with a brass rod or something similar.
- Keep pressing until you've bleed all the air from the master cylinder.
- Remove from vice and install in Corvette.
- When bleeding the brakes, NEVER let the master cylinder reserviors run dry. If they get dry, air is reintroduced to the master cylinder and you have to bench bleed again.
- Also, bleed your Corvette calipers in order from the fartherest caliper from the master cylinder. Start with right rear and end with left front.
- Pressure bleeding does the best job, but requires a pressure bleeder. Having an SO or a buddy press the brake predal is also better than vacuum bleeding. I only use vacuum bleeding to draw the brake fluid into the caliper and use a pressure method to push out the air bubbles.

On my 1977 Corvette, I believe the rear calipers have two bleeders each (based on memory and it's been awhile). Both bleeders, with calipers installed on Corvette, face the front. It may be different with your calipers.

Please let me know if you have other questions.

 

Thanks lowvette!!! I think I have found the problem. I went back and bench bled the master cylinder and re-bled, using pressure(SO), starting at right rear.. That did help some but, I still did not have a truely "hard" pedal. As I was calling it quits for tonight and cleaning everything up, I noticed a small puddle of fluid on the floor. Sure enough the right rear caliper is leaking fluid. I will try to remove it and find the problem sometime this week.
Thank you for your suggestions and help. It has helped me learn a little more about my Vette.

Mike

 

Sounds like you're getting there. Are your calipers stainless sleeved units? If not, you might want to look at simply replacing them with sleeved calipers (Vette Brakes sells them). If they're not stainless, look to be doing this same thing every spring.

 

If the leak is near the bleed screw, it could be a cracked caliper. I've seen this happen more often when speed bleeders are installed. Overtightening a bleed screw can sometimes cause this as well.

Glad to hear you're moving in the right direction.

 

There are two bleeders on each of the rears. Both have to be bleed.

 

Yup. The calipers are basically 2 halves with pistons on each half. Each half of the caliper has its own bleed screw. So there's one on the inside of the rotor and one outside of the rotor. That doesn't sound quite right, but there are two.

THis pic should help. The two halves of the caliper are basically mirror images. See the bleeder screws pointing to the lower left corner of the picture?