I have a problem with my brakes.  I don't know if it is the calipers or master cylinder.  I have a lot of brake pressure prior to cranking my car.  However, when I crank the car the brake pressure is minimal.  My master cylinder is full of fluid.  Is this a problem with the brake calipers, bleeding the brakes or the master cylinder.  Does anyone know which of these may be causing the problem.

I am going to assume you mean start the engine when you say crank the car, and that the brake pressure is peddle pressure.  If that is the case, you are probably losing vacuum in the brake booster, which builds up again after running the engine.  If all that agrees with your symptoms, check for a vacuum leak in the hos to the booster, in the check valve, and in the booster itself.  Unfortunately, the most common problem is a bad booster, which is a pain to replace.  Good luck.

Larry

Does the car stop ok, or does the pedal go to the floor?
Power brakes will normally have a "hard" pedal without the engine running. Once the engine is running, the booster makes the pedal much easier to mash, hence the "power" brakes.
If the car stops ok with a good pedal, I'd say you're ok. If the pedal is going to the floor with the engine running, then you probably either have air in the brake system, or a bad master cyl.
More details are needed to confirm the problem...

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Joel Adams
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The pedal is going to the floor with the engine running

Now we're gettin somewhere!
You need to check all four wheels/calipers for leaking first. Corvette calipers are notorious for leaks if they sit very long.
If there are no external leaks evident on any of the calipers, and the Master cyl is staying full, without having to add to it, then you have:
1- Air in the system
2- Bad Master Cyl.
3- Excessive rotor run-out(see #1)
4- Combination of all of the above...

For issues #1 & #3, excessive rotor run-out, or "wobble", will cause the pistons in the brake calipers to act as pumps, sucking air into the brake system. This is a '65-'82 Corvette anomaly...other cars don't have this issue.
If you can bleed the brakes fully, and the brakes are great until you drive it for a while, you probably have warped/out of round rotor(s). They will need to be turned/trued, or replaced. This is THE #1 problem with Shark brakes...

IF the pedal never pumps up, even after bleeding, then your master is most likely gone to Corvette heaven, and will need to be replaced.

So....check for leakage first, then bleed thoroughly. If the problem still exists after that, the master is bad.
hth

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

irlene,

thanks everybody, I will try to bleed the brakes when it is a nice day here.  Right now it is rainy and a little on the cool side

Hey Irlene, I have relatives in Cary - is Red Springs anywhere near there?

Keep in mind, with our cars when the car is sitting still, it is possible to pushthe power brakes almost all of the way to the floor when there is nothing wrong.  Is the pedal okay when the car is moved?