Todbo

Getting a crappy MC is bad , how about a brand new heater core from auto zone , I still haven't decided if I'm going to take the damn thing back out! :mad

Larry B.

It's the grease in the waterpump bearings that makes the difference. There was a thread on that on the ncrs board.

Brian Madderom

Ecklers has new Delco for $199 and VBP has new Wagner units for $79. Not sure about Mid-America but I would do my homework on Manufacturers of the parts.

phoenix

Alright... now for some reason it has to be the power booster.

I replaced the mastercylinder with a new one. Raybestos.

Same problem.

The brakes are nice and firm with the engine off, then the pedal drops to the floor when I start it up. At idle, I am getting about 10-13 psi of vacuum at the booster. The check valve is working and the booster holds vacuum, but not for long. When I shut the car off, the vacuum holds for about 2-5 minutes.

At idle to about 20 mph, if I stomp on the brakes, the pedal goes to the floor and the brakes slowly stop the car. Over about 20 mph if I stomp on the brakes, they are hard and will lock up.

The are all bled well (again) and the same exact problem. The only thing that I haven't replaced is the power booster.

So I ordered one in the hopes that the problem will be fixed finally

Maybe I have a small leak in the diaphragm that won't hold a little vacuum but will hold it at higher RPM???

Any other ideas??

Matt Gruber

this sounds like the problem of low vacuum. I had the same problem with the 350hp cam. Crummy at 20mph or less. Might improve with new booster. Mine is old. 262 cam fixed the problem in my 72.(strong vacuum, at least 15")
Sounds like a vacuum leak or a big cam. A vacuum canister will fix it if it is a big cam.

71coupe

Looks like bad master cyl. If the bore is tapered or not honed on the rebuild, the piston will only seal/pressurize when the pressure is high, like when you press hard on the pedal (which forces the seals to the cyl wall)

The thing that kills master cylinders is when the pedal goes to the floor. The piston & seal are pushed into an unused section of the bore - which usually has a ridge & is dirty. That tears up the seal.

Look around for a company that can resleve the master cyl (similar to the stainless sleves that are installed on the wheel cylinders. I saw an ad a few years ago in a Corvette mag that installs bronze sleeves- which is better than the virgin metal after a hone. I need to do my m/c as well. Good luck.

GTR1999

White Post Restorations in VA resleeves M/C's for about $150 with a lifetime warranty.
Gary

MIKER

Looks like a good opportunity to upgrade to hydraboost power assist like Norval uses.
Norval's ps assisted brakes http://forums.corvetteforum.com/zerothread?id=222342