Brake Issues..Need input

[ABX131]

My 63 has the running gear from a 76 4x4, including the axels and brakes. It has disk front and drum rear. We replaced the M/C and booster a while back with a remanufactured unit, we bench bled the M/C. The application is for a 68' Vette. We had the front rotors turned at the high school auto shop my son is in and they put new front pads in. The rear was good and needed no attention. We have bled the system and have no air in the lines. We have bled them a ton. The issue we are having is the brake pedal has too much travel and feel like they loose pressure and the truck will start to creep at stop lights. The pedal has a return spring?? Why would it need one? Shouldn't the pedal have enough pressure to push it self back? My son and I are having different theories as to what our problem is. He thinks the rotors are too thin explaining the long travel of the pedal. I think the M/C is not holding pressure thus allowing the truck to creep. Input please..

[Wrenchbender Ret]

First check the adjustment of the rear brakes. They should be snug in the drums. You may have to back the emergt. brake cable adj. up. If it is to tight it will pull the shoes off the anchors. You may need to adjust the rod bretween the booster & master cyl.
If the pedal goes down as you set at a light & lose the brakes you may have a bad master cyl. The thin rotors will not cause this. The caliper stays up against the pad.

[Tx Firefighter]

With the Vette master cylinder, you might be running into issues with the fact that your rear brakes are drum and Vette rear brakes are disc. Perhaps a lack of residual valve, being a Vette master cylinder ?

[ABX131]

What about the return spring, did some one add it or did they all come with one?

[luvbowties]

""The pedal has a return spring?? Why would it need one?""

For one thing, spring would keep brake light from staying on from pedal sag.

On other issues, why did you use a 'vette mc? You would be certain that all components match had you used one that fits the donor truck... Another possible problem: often, during upgrading, the push rod length from brake pedal to booster needs adjusting(extending, probably). HTH,
sam

[luvbowties]

...another possible issue: suppliers, at least some, offer a mc for 68 vettes using a 1-inch bore and a different part# for those using a 1 1/8-inch bore. Also, the ones for manual brakes look just like the ones for power brakes, altho' they have different part #'s. As others have mentioned, that 'leak-down' at stoplights sounds like a failing mc.
sam

[ABX131]

Issue fixed...replaced M/C under warranty and adjusted linkage..solid stopping power now..Thanks to all. Next week hope to swap out the steering column.