lonestarclassics

hi everyone. new to the forum. I have a 67 fast back that I recently purchased. it has 78 thunderbird brakes (new calipers, rotors, hoses, and pads) with I drum drum power master. when I bleed the brakes it pumps up fine but will not release the pressure from the front caliper. any thoughts??

Starfury

Pinched line or a stuck caliper piston are my first thoughts. Is it just one side, or both sides on the front?

Edit: If it's both sides, 67mustang302's comment below makes perfect sense.

67mustang302

You have to use a disc m/c with disc brakes. Some drum m/c's have a residual pressure valve to counter the force of the return springs in drum arrangements to prevent low pedals when you reapply the brakes, and if you use it with disc brakes the calipers won't release completely.

lonestarclassics

im getting a thunderbird master in a minute. everything else is t-bird so ill stick to it I guess

bop11

When you say it does not release, do you mean the pads are tight against the disc or that you just can't see them move back? There is no return on disc pads. The pressure is released but the pads stay against the disc unless there is a little warp and then they will be pushed back by the warp in the disc, but in general there should be no movement of the pad only pressure. If the pads move away, it means you have a problem with the feed valve in the master cylinder being stuck closed or sticky.

lonestarclassics

the pressure does not release. have to use a pry bar to turn the rotors. and as I said. everything is new in the system. installing a disc/drum mc now. the residual pressure valve that 67mustang302 was talking about must be the problem

67mustang302

It might be the problem, or part of it. You might also have stuck pistons. In either case, you need to run a disc m/c with discs.

bop11

On early mustangs the front section of the master goes to the rear brakes and the rear to the front brakes. It is not a cross (one front and one rear) as on newer cars. I don't know what a 78 T bird had. The lines go to a broken line detection switch before they go to the brakes. The switch is just a piston which moves to one side or the other should the brake lines fail. This cuts off the circuit so you don't lose all the fluid and all the brakes. If you have it setup with the cross system, the rear drum return springs may be holding the front calipers on.