My brakes feel spongy when I apply then. The pedal goes to the floor and car takes considerable more distance to stop. No fluid is leaking. Any ideas why?

 

Could be a few things. The first thing to come to mind is that your master cylinder has a leak. The other things could be air in the lines, very worn pads, etc..

When you apply the brake, if you give it full force braking, does it still lose pressure, or is it only when you give it light force braking? My master cylinder experience has been that it will leak vaccum when just barely touching the pedal, but when using a lot of force it works ok.

Either way, get this fixed pronto! :yesnod: :yesnod:


[Modified by Glock'94, 4:51 PM 3/7/2002]

 

Deteriorated seals in your master cylinder ... or air in the break system.

 

Have you tried bleeding the brakes?

 

That will be my first fix. Its the cheapest!

 

This seems to be an ongoing problem with some members including yours truly. I just had a new GM master installed...my pads are fairly new, ss lines and such, it feels the same way as the previous re-man master cyl which the installer insisted on that causing the problem. Not the case. It was bled, but there could still be an amount of air in the system. Mine are mush around town, pedal goes to the floor if you're at a light. And when you make a fast stop, the pedal seems to firm up.

A friend said a special technique requiring a machine might get the air out of the system and resolve the problem.

 

I would look at the slave cylinder for what you just described, since you have replaced the master cylinder. Are you loosing any fluid?

Original poster.....check brake pads for excessive wear. Bleed out system. Good time to install speed bleeders if not already.

Also wanted to mention the soft brake lines might just be swelling excessively for some reason. Old fluid that needs purged.


[Modified by Goody, 3:44 PM 3/8/2002]

 

If the pedal slowly goes to the floor then MC is suspect (or leak). If the pedal feels spongy but will pump up and brake better, then air iin the system is suspect. Brake light should come on if the pedal goes too low, or if the abs (think it's the abs) senses a pressure differential between wheels. Usually spongy pedal or brake light (if fluid is full) means air in the system.

Master cylinder could have air in it. If it does it needs to be blead before the calipers. First you have to make sure the front of the MC is lower than the back of the MC. Jack car as necessary. Pump up MC to moderate pressure and crack the front line enough to dispell any air, tighten fitting before releasing the brake pedal. Repeat waiting 15 secs (this in shop manual) until all air is removed. Repeat proceedure with rear brake line on MC.

Check ABS unit for a bleed screw. If it has one (some do, depends upon year and I don't know), this should be blead next, however I don't know the correct proceedure to clear air from this point. It may very well require a Tech I / II scan tool to cycle the abs modulator to clear this point. It may not, you have to check the shop manual for your year.

Then move to each caliper. Remember this is a Corvette and the abs unit is located behind the driver in the center right side of the car, so bleeding order is different than other cars. For my 89 the bleeding order is :

1.) Right Front
2.) Right Rear
3.) Left Rear
4.) Left Front

I would do a complete flush which requires a little more than 1 full quart of fluid. Do not use DOT 5 (silicone) fluid. It may take a long time to get all the air out. If at any time the MC goes dry, start over, you blew it.

I would love to hear what all these spongy pedals turn out to be. It's very hard for me to believe that all of these are just air, can't any shop bleed the brakes anymore? I think most shops know how to bleed brakes, so maybe it's air trapped in the ABS or front of the MC, but most shops know about that as well. Perhaps the Corvette with the low mounted ABS unit in the center of the car is just very prone to getting air trapped if allowed into the system from the MC.

Let us know what it turns out to be.

Pete