'68 Mustang bad brakes...

Just from your description, it sounds like you have a bad master cylinder, it happens even to new ones sometimes. If you pump the brakes with the lid off the master you will get fluid spraying around so that part is somewhat inconclusive (but don't leave the lid off!) StuK

(The only thing that hasn't been replaced is that directional valve 'thingy')

Do you mean the proportioniong valve? You'll need one for a disk/drum setup. Did you bleed the master cylinder?

Thanks for the quick replies Stu and Mark.

We're onto the second master cylinder. Both were bled properly although we can't get pressure to build up in the lines. If the lines are pressurized slowly as the brakes are pumped, the pedal will always travel to the floor. If pumped quickly, they will pressurize but we're not getting any air out!

Yes, the proportional valve. I think it's stock for the all drum setup. There's another one for front disc/rear drum?

Yah.

Thanks again, Darryl.

Make that the *proportioning valve.

Ok, we might not be talking about the same proportional valve. He's calling it a pressure balance sensor block which to me sounds like a proportioning valve but he says it's different. Apparently this one is new (aftermarket) and it has a thumb screw to adjust the pressure to the brakes (i.e., reduce it to the rears and increase to the fronts). Right now, he barely has rear brakes and nothing on the fronts so we're going to remove that block and see what happens.

Any other suggestions?

Darryl.

be the master cylinder is bad(its the oring on the part that goes into the opening --the main piston... had it on a 66 mustang.. had the brakes worked on at a shop back in the late 60's... the pedal would stay up but if you leave a little pressure off the pedal it would travel to the floor.. the mechanic(old man) told me that someone must have shoved the pedal down to far when they bled the brakes... that would mess up the master cylinder piston(O-ring)..... it hits an area that it never does when the brakes have fluid in them so it then gets distroyed by this NEW area that it hits during bleeding....kinda makes sense if that is your problem.... hope this helps.

All post and replies kind of vague on a few points. the distribution block is the brass unit directly down stream of the master cylinder on your car it should have a wire coming out of it. This is what will light up the brake waring lamp in your guage cluster. You spoke of bleeding the master cylinder, have you bleed both rear wheel cylinders, and both front calipers? On a swap as you mentioned this may require filling the master cylinder several times. The proportioning valve mentioned in other posts is to limit the flow of fluid to the rear wheels as the calipers take much more fluid to operate. Fluid spraying back into the master cylinder while holding (not pumping) the brake pedal down is a sure sign of compressed air in your system.

Darryl... Been there, done that. I can almost promise you the master cylinder does not have a big enough bore to push enough fluid for the new disks... I've been there. What is the bore size of the master cylinder? I'll bet it's less than a 1" bore...like a 7/8"?? I had to go to a 1 1/8" bore to push enough fluid to make the fronts work. Let me know what bore size you are using for the master cylinder? Mark

Hi Mark,

I would let you know the bore size if I knew which measurement that is! The push-rod bore is 1/2"--this is bored into what looks like an aluminum part that is retained by a snap ring--the apparent outer diameter of this part is 1"

I suppose that I can pop off that snap ring and take a closer look. Can I pick up an oversized master cylinder or is it possible to have this one machined?

Thanks for the feedback, Darryl.