After installing new power brake booster and master cylinder on my '76 Comet now the front disc brakes are locked. With the wheels removed I cannot turn the rotors by hand. If I pull the calipers and push the pistons back in, will they return to normal braking or will they just stay tight after the first time I use the brakes? Any ideas what might be going on here?
Were the calipers sitting for a long time? That can make them hang up or seem "sticky". Did you try to drive it yet? If not I would try a little bit of low speed parking lot type driving to get the calipers and pads to settle into place. See if that makes a difference. If you are sure the caliper pistons are not sticking and a little test drive does not settle it in, I would suspect somethings not right with the master.
The car did sit un-driven for only about two months. I've driven it a little now. Just around the block. Gentle pressure on the pedal and the car jerks to a stop. The master cylinder is brand new from Auto Krafters.
If the rod in booster is too long, can cause the "dragging/locking brake syndrome". Should be checked for proper clearance prior to install. Loosen MC, if brakes free up that's the problem. After already installed, easiest way to set is shorten rod by a turn and try brakes. When too short, there will be free travel prior to brakes appling. If still hangs, calipers are probably giving issue. If above doesn't fix it, open bleeder valve to see if their is pressure in line. If OK check distribution block and/or move on to longshot. Longshot, possibly you have a drum MC. Drum brake MC have a check valve in the front brake port that prevents shoes from fully retracting. Generally they don't seal perfectly so work OK with a disc setup(case in point, my Fairlane that got disc conversion last week). If that's your problem, loosening the front brake line at MC will relieve the problem.
Okay, here's what I did after lunch. Pulled the calipers off and pushed the pistons back. Then I pulled the master cylinder and shortened the push rod from the booster by about a turn maybe a little more. Put everything back together and did just a short back-and-forth in the driveway. Brakes felt normal. They feel pretty good actually. Don't have time for a full test drive today and it's about to start raining anyway, but I think I've got it. Thanks guys for the advice. Keep your fingers crossed.
Glad it worked but it wasn't necessary to compress pistons in calipers. Anytime vehicle is held stationary with brake, caliper pistons will be against rotor. Next movement of vehicle leverages pads away from rotor. With rod too long, it was exactly as someone was continually holding brake.
"You got it just in time to make the MCCI Roundup "at your front doorstep". Yea, no kidding. There was a point a couple weeks ago when I was sure I wouldn't make it.
I had that problem in high school, the rod was too long as described and would lock my brakes. Being young and ignorant I was cracking the bleeder regularly just to drive. Grandpa came to the rescue, backed the nuts off the master about a 1/4 inch and all was well. He then "showed" me how much fun it was to adjust the rod under the dash. Showed = "get your butt under there and adjust that rod before you kill someone!".
Just got back from a good test drive. Brakes worked great. The only problem now is the speedometer has stopped working. Pretty sure struggling around up under the dash I must have pulled the cable loose or something. Not a big deal, I'll get back under there at some point. I hope I never have to change out a power brake booster ever again. Terrible job. Might be better and certainly easier to just sell the car. Only kidding. (not).
