Interesting brake issue
 

These brakes on my 69 Firebird track/street car have me a little baffled. Ron Sutton put my complete system together based on what I want to do with the car, weight, tires, etc. Willwood 6 piston in front with 4 piston in the back using Spec 37 rotors, Willwood 7/8 master (already rebuilt by Willwood and bench bled) with Motul 600 fluid.

I initially bled the system via gravity, vacuum, pump and hold. It took a while since the complete system is brand new...including the copper lines that I bent. I then drove the car about 50 miles in hopes that the vibration and bumps from the road would release and residual bubbles still in the system. I then repeated all the bleeding procedures. I then went out to bed the pads in.

I drove the car on a couple occasions and wasn't thrilled with the stopping power (I couldn't get the brakes to lock up if I really wanted to). I was also having trouble with my brake pedal not returning all the way up after being depressed, which caused the brake switch to remain activated...thus the rear brake lights would stay on unless I put my toes under the pedal and pulled it up all the way.

I briefly talked to Ron via email and he suggested to rebleed the system with the rear off the ground a foot or 2, adjust the brake pedal so the master was slightly preloaded, or a combination of the 2.

I rebled the system, and added reverse bleeding to the regiment. I also adjusted the brake pedal rod so it was twisted out far enough to give a slight drag on the brakes while at rest (it is in the upper pedal hole). No air in the pedal as far as I can tell, and the pedal springs all the way up now (no brake switch problem).

Took the car out for a short drive today to test things. I made about 6 hard stops from about 50 and was able to get the rears to lock up (too much rear bias...still a adjusting the proportioning valve. but after about 3 miles of driving the brakes began to lock up! It was so bad that at one point it was like I was power braking the car as I was trying to get to a stop sign and then pull over. I shut things down and got out to check under the hood, under the car, etc. All looked normal, so I got back in and fired it up, but it in gear, and it wouldn't move...brakes completely locked up! I sat there for a bit scratching my head. 2 different cars stopped to see if I needed help...gotta love back country roads in Iowa. I decided to just get in and give it hell. I was able to get moving, but was worried I was going to really mess something up. As I was moving, I did the toe thing with the brake pedal. After I put some pressure on the bottom of the pedal, the brakes seemed to release and all was ok. I applied the brakes twice more on my way back to the garage. I jacked the rear of the car up to see if I could rotate the tires. I could, but it was VERY hard...same on the fronts. After the car sat for a while, the wheels were easier to spin. Sorry for the long post, but I am sitting here wondering "what the heck is going on". I am waiting to hear back from Ron, but he has a few million other things going on at the moment. Anybody have any ideas?
Joe

You need free play in that pedal. The pressure can't bleed off if the pedal does not release all the way .

I also am concerned about using copper tubing for brake lines. Copper generally does not hold up to vibration very well. Maybe I am reading what you wrote wrong ?

It's probably NiCopp. Copper/nickel alloy I believe. Not pure copper. It's supposed to flare much easier than stainless, yet resist corrosion better than regular steel.

Yes...NiCopper....the good stuff from England. Maybe I took Ron's advice a little too literally!

If you having to pick the pedal up, make sure you do not have an interference at the firewall. Also make sure you have the calipers shimmed within spec. If you have a pad riding on the rotor, it could build enough heat to push on the rotor if it doesn't have proper clearance.

I figured I had to do the toe thing to get the brake lights to turn off because of a combination of the brake light switch not properly adjust and the brake pedal rod not properly adjust for length. Today's problem didn't show up until I lengthened the master cylinder push rod end...to preload the master.

Preloading the master cylinder sounds like a bad idea to me. The piston in the master cylinder needs to be fully uncompressed when your foot is off the brake otherwise the port to the reservoir will be blocked off, and believe me it doesn't take much movement of the piston to block off that port. You also won't be able to bleed the brakes when that port is blocked by the piston. The booster to master cylinder rod needs to be adjusted such that there is a small gap between the rod and the piston of the master cylinder. Then adjust the rod length of the other side of the booster to fix the brake light problem.

Also make sure your parking brake is working. It could be that the pistons in the rear caliper is having to travel too far because the parking brake has not been adjusted.

you don't preload the master. it has to have play so there is no pressure on the brake system when your not using it or the end result is your brakes trying to lock up.

Manual system....no booster.