Need Help please - Non ST

[Mark Grumpy]

TAKE IT TO A NON ST SITE :lol:



I come here because there are no other good sites for this kind of help and I'm looking for someone to support my conclusion.



Anyway - my Corvette has brake issues. Non ABS, 4 wheel disk. No leaks, good pads and rotors.



The pedal went almost to the floor and the light came on. My first thought is master cylinder either dirty or bad internal seal (or both). This logic may be flawed but if it were either booster or vacuum the pedal would be harder, no? Agree or other??



thanks



Mark AKA Grumpy

 

[troy malone]

brake boosters tend to make a hiss or air leak sound when they go bad.. i still had brakes on my vette when the booster went,, just had to press real hard and the pedal did travel more..

i'd try bleeding the system and changing the fluid if you havent done that already, could be air in the system..



troy



what year vette???



mines a 88 35th anniversary #1580

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[Mark Grumpy]

thanks Troy. I don't hear anything and the fluids were changed last year sometime. I'm thinking for 30 bucks I'll just go ahead and change the master out. It is an 80 and I'm not certain it's ever been replaced, so it won't hurt to do it.



Not a good pic, but here she is.



grump



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[P M]

As TroY said, Air. Bleed the system first before you replace any parts.

 

[Fred]

Agree with TroY and PRM. Bleed. Then replace the M/Cyl.

 

[Yardsale]

Almost to the floor? Seems like more than air (or a lot of air). The light comes on if A) there is not enough fluid (assuming there is a sensor in the reservoir) or B) if one of the pistons in the master cylinder has enough of a leak to cause the Pressure Differential Switch to close the circuit or C) if the front or rear balance is off enough for the Pressure Differential Switch to close the circuit (which can be caused by a bad seal in a caliper).



My guess is that something is blown. If one of the calipers is blown, I would think that there would be some pedal loss, but at some point there should be pressure before the pedal gets to the floor (or almost) Possibly an external leak.

 

[Ralph Pipkin]

I have owned and restored Vettes for many years. If you have no leaks and the pedal gets spongy I'm afraid you could have a costly problem. From 1965 to 1982 Vette owners begin to experience spongy brakes after the rear wheel bearings started to wear. As the rotors rock back and forth taping on the pistons in the calipers it would pump air into the system. The parts are relatively cheap but the labor is high for this work and requires expensive tools to facilitate repairs. This is one of the type of repairs that tend to precipitate additional work. Typical cost are around 2K. Hate to be the bearer of bad news and this may not be your problem but it bears checking before spending money and efforts elsewhere. Good luck!

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[Kevin Palmer]

Grump, if the inner seals are worn inside the Master Cylinder, what you describe may happen.



Here is how to test this. Drive it around a bit to get it to temperature. Come to a stop like you normally do, once stopped, instead of just resting your foot on the pedal like normal, press a bit harder like your still trying to stop for example. If the pedal moves down only a slight bit due to the extra pressure and does NOT move then try this.



Come to a stop like normal, once stopped, relax the pedal a small amount and then reapply the pedal with a smooth light pressure. If it goes past the normal resting area and works its way to the floor you need a master cylinder.



They fail fairly common in that general year area. I have changed HUNDREDS of then for customers.

 

[Kevin Palmer]

Did you get a definitive answer???

 

[Mark Grumpy]

Not yet. Thanks all for the suggestions to change fluid first. I picked up a master cylinder and will change it and the fluid. I figured for 20 bucks and five more minutes what can it hurt?



Hornet - would what you describe cause a vibration at all? I've been noticing a vibration that "feels" like it is in the drivetrain but vibes can be decptive sometimes.



thanks



grump

 

[Richard L]

I would say that you have air in your brake lines or you have a leak. It sounds like you may have let your fluid get low and it sucked in some air. The air in the brake lines will compress and make the pedal sink without much brake action. That will also cause a pressure imbalance that will trigger the "Brake Light".



Power brake booster failure will not trigger the Brake Light. That is caused by excessive pressure differentials between the front and rear brakes. That is a hydraulic problem.



...Rich

 

[Ralph Pipkin]

When the bearing wears it does not necessarily vibrate. You can check for free play as you would for any wheel bearing. More than a couple thousandths will cause rear brake problems. After you bleed the brakes if the problem returns you will need to get someone to check the rear spindles. You can spend a lot of time and money chasing this problem if the bearings are shot.