Finja

Ok, so I finished installing all new brake components. I mean new booster, master, all the lines, proportioning valve, rebuilt the calipers. I reused the rotors and pads because they were still good. Everything else is new. I got the kit from Zip Corvette.

Finished bleeding the brakes the first time by using a vacuum gun. This worked fine on the rears but could get no fluid through the fronts with out pumping the brakes. So......had to use the old pump, hold, loosen, tighten, do all over again method on the fronts. The brakes were working fine so went on about a 10 mile drive. On the way back to the house, and after a few stop lights, noticed that something was dragging pretty bad so I pulled over. The front pads were smoking! Put the car in drive and it sits still. They were locked up. during this time noticed that the brake pedal was hard as a rock, even with no vacuum on the booster. After a little while they cooled off and I was able to drive home. Now the pedal goes all the way to the floor and the brakes hardly work..........Any ideas??????

...Roger...

Sounds like the front are dragging. Open the bleeders and see if the drag goes away.

Finja

Well the drag went away after I let them cool.

...Roger...

You have to find which part of the hydraulics is bad. The rubber lines are the usual culprit but the master or a misadjusted pedal can cause it also.

Mike Ward

Here we go again. Start there, looking for a master that doesn't release when hot.

Finja

Rubber lines are all brand new.....How do you adjust the pedal?

Finja

Its brand new......is it common for new ones not to work right?

7T1vette

Dragging brake pads is one thing...partially applied brakes is different [worse]. In the first instance the pads can get hot and burn on the surface, plus maybe even warp the rotors. In the latter instance, you can generate some serious heat up to catching the pads/tire on fire.

If the pads are dragging, it could be that there was zero runout on the rotor. You need a few thousandths of an inch runout to keep the pads from staying on the face of the rotor.

If the brakes are partially applying...but only on the front, then they must not be completely releasing pressure after you exercise them. That would either be due to a sticky proportional valve and/or a sticky master cylinder piston that doesn't release fully. I would lean more to the P-valve being sticky.

'75

On my 75 there is an adjustable push rod between the master and booster. If it's adjusted to far out it can cause these symptoms.

...Roger...

I would try this. Get the front wheels off the ground. Rebleed to get your pedal back. Pump pedal up and see if fronts will lock up. If they are locked loosen the 2 nuts holding the master to the booster. If this unlocks the front calipers the length of the pushrod might be not letting the master return. Try moving the master back against the booster to see if the rod is hitting before the master bottoms out. If it is the pushrod is too long.

If the above doesn't unlock the calipers, with the master still away from the booster try loosing the front line nut on the master and see if fluid escapes under pressure. If this releases the calipers the master is holding pressure for some reason.
(Careful not spray brake fluid on your paint)

The pedal pushrod inside can also be too long but you should notice no pedal freeplay.

...Roger...

Quick question. Did your new master and booster combo require brass adapters at the 2 brake lines going into the master?

Finja

Ok, this was a concern to me. The booster came with a short rod in it, the master came with the same size short one and a long one. I decided to use the long one because the hole inside of the master cylinder piston was really deep. When assembling the rod didn't seem to put any pressure on the master cylinder piston. The instructions with the booster said that if you have the correct length rod that fluid should come up in both when pushing the brake pedal about 1/2", and it does.

I will try this tomorrow........


No, the master has the correct size to match the lines coming from the proportioning valve.

Mike Ward

Roger's got it.

Finja

Ok......So I didn't need to bleed the front brakes this morning, they were working fine. So I took a little drive, about 5 miles. Stopped at one stop light to turn around, and on the way back same thing happened. I pulled into the drive way and she stopped herself with out me touching the brakes. I turned her off, got a wrench and loosened the two nuts that hold the master to the booster and the brakes freed up! So I decided to try it again, tightened the bolts back up and went on a little drive. The brake pedal was going almost all the way to the floor and I couldn't get them to start dragging again.......

Not sure why it would do it once and not a second time. Also sounds like the push rod is a little too long. Mine is not adjustable....Can I buy an adjustable one somewhere or should I just grind a little off the current one?

...Roger...

Before deciding the pushrod is the problem, try putting a couple washers between the master and booster. ( gently push the master up to booster and note the gap-this is the amount of washers to use) Drive the car , if the problem stays gone then work on the pushrod but if the problem comes back you might have a problem on the booster side.

I've been running into booster/master combos that are not matched.

Finja

OK, looks like it was the push rod being about 1/4" to 1/2" too long. I put three washers on each side between the master and booster and everything seems to be fine. Drove it a pretty good distance today and the calipers were still cold afterwards. I guess now I will just cut a little off the pushrod at a time until I get the right length.

Thanks to everyone for all the help!