BIG BLOCK JAMO

i just bought a 66 427/425 roadster in detroit. the car got 4 stainless steel calipers about 15 years ago. it sat for a while after that. i've blead the brakes. no visable leaks. the pedal "pumps-up" but then gets "spongy" and then almost goes to the floor. is it time for 4 new ss calpiers?? any sugestions?? thanks in advance...

JohnZ

If there are no visible fluid leaks, you're bypassing the piston seals in the master cylinder. Rebuild the master - if the bore is pitted, get it sleeved.

DansYellow66

If there are no visible leaks at the calipers then it's more likely the master cylinder needs rebuilding in my opinion. They could also just need more bleeding. What technique did you use to bleed the system?

Avispa

Also don't forget to check your wheel bearings front and rear for correct adjustment, and the rotors for excessive runout. Loose wheel bearings or excessive rotor runout will do the same thing.

You may also have a tiny pit in one or more of the SS sleeves (just note that this is the least likely problem, check all the other stuff first). When I bought this 66 about 25 years ago it had an air pumping problem into the driver's side rear caliper. The bearings were adjusted and the rotor runout was within spec. After disassembling the caliper, we found a small corrosion pit right in the seal lip area. After replacing the caliper the problem was finally solved.

MikeM

My vote is a caliper is sucking air simply because I don't recall a mastercylinder ever causing a spongy brake pedal. Not saying it can't, just never seen it.

If it's a caliper, you may have to remove the wheels to find it. Caliper leaks can be sneaky.

mrtexas

The way to verify the problem is to block off the master cylinder and see if you then have a pedal or it is spongy. If spongy the master cylinder is to blame. If not, air in the brake lines requiring bleeding.