i have all new brake components. when i try to turn the rotor without the tire it won't move. i pried the piston back just a hair and they seem to rotate easy after that. i don't understand why the piston doesn't release by itself. any suggestions would be appreciated. thanks bob m o No:
Did you replace the master cylinder with one designed for disc brakes? Some drum m/c have residual valves built in them that will keep pressure applied after the brakes are released. This was done to keep the pistons expanded in the wheel cylinders and also to overcome some of the return spring pressure. Youu need a m/c that does not have this internal to it. Sometimes these can be removed. Also due you have freeplay in the m/c pushrod. If not the m/c will not release all the pressure. Hope this helps.
If the bushing the bolt goes into is scored, it might prevent the caliper from loosening. I had that problem once, but not on a Buick (it was an 88 Cutlass).
thanks for all your info. all the brake components are new or rebuilt including hoses and steel lines. the only thing not new is the combination(proportioning) valve. also it is both rotors and i do have a little freeplay in the pedal. the m/c is drum/disc also.
Did you lubricate the mounting bolts and caliper ear bushings with synthetic silicone grease? For the calipers to operate properly, they must be able to slide.
10-4 on the lube. i think i'll pull the m/c and check to make sure it doesn't have that valve for drum brakes. thanks for the reply. bob m
The valve is usually located behind the flared seats that the lines screw in to. If you pull the lines off try and push a small piece of wire (welding rod) in the hole. If it hits something before it goes into the bore then that usually indicates their is a reidual valve in that port.. Some times you can remove them by screwing a sheet metal screw into the seat and pulling it out with a pair of vise grips. Then remove the valve and reinsert the seat. Doesn't always work that easy but might be worth a try.
I discovered the same thing on Shari's GS with rebuilt master cylinder and recently added booster. Like you I checked the play on the booster rod going to the brake petal and found it slack. I ruled out the hoses acting like a check valve since they had been replaced in the last few months. Ended up putting a couple of washers between the booster and the master cylinder to give the plunger a little end play. That cured the problem.
problem solved. it was a check vavle in the m/c. me to parts guy "is this a disc/drum or a drum/drum m/c" ? parts guy "it's definetly a disc/drum m/c." ou: i guess you have to double check everything, if you want to be right and save a lot of time. thanks to everyone for response :beer bob m.
