79Grrr

Im a nubbie!! I bought a 79 vette about 6 months ago. (What a dream!) however i have replaced the master cylinder twice and my breaks in a matter of days are mushy.All the way to the floor. Someone had recommened replacing the proprtioning valve. Im fustrated cuz winter is coming in any day now and i need to drive my beauty and go get it winterized for the first snow fall.Any help would be greatly appreciated!!! stumped in Idaho

VETTEVIC

A mushy brake pedal is a sign of a good master cyl. If it were bad it would be less than mushy without stopping the car. Mushy pedal is either a problem with air in the lines or a caliper leaking or a line leaking somewhere. I'd check the brake lines (every joint) with a clean paper towel for any moisture or signs of leaking then pull the calipers and make sure they are sealing properly. Most likely there is just air in the lines from the master cyl. replacement but dont put money on it. A proportioning valve will not usually cause mushy pedal unless it is leaking, usually causes either the front or back not to work and the pedal too hard.

Beasley's 76

Also did you follow the right sequence when you bled the brakes, this caused me some problems as I didn't realize you had to do it in a certain order. Search the forum and I know they were posted on here somewhere, once I bled my the correct way my brakes are better. I had similiar issues until then I replaced the Master cylinder and I would have breaks when I left the house but before I got home they were going to the floor. Sorry I don't have the directions handy but they should be posted here somewhere.

79Grrr

I never expected such a quick response!! Thanks!! Im bent on driving my vette before snow gets here.!!

BerniesVette

Check all 4 calipers to see if they are leaking. If they are You can exchange them at auto zone with ones that have a lifetime warranty or go with upgrades. Bleeding the brakes must start with the caliper farthest from the master cylinder. Usually the right rear, then left rear, right front and left front last. The rear calipers have two bleed screws and both must be bled. I believe the bottom screw first then the top. Someone will correct me if I'm wrong. I hope this gets you some good strong brakes!
Bernie

VETTEVIC

The bleed screws on the rear calipers are both at the top, one to each side. Bleed the outside one first on both left and right.

jayr

I found that my calibers would seep but not enough to leak on the floor
or even noticable crawling under the car. It would give me a mushing pedal from air leaking in. I got mad one day an pumped my brakes as hard as I could and held them for about 5 minutes. Than took each tire off and found two of them damp with brake fluid.

wombvette

The problem is runnout in the rotors, especially in the rears. The master cylinder is good, quit F%&^*ng with it. There are probably a thousand post in the archeves on this problem.

genuine1980

Did you remember to Bench Bleed the master cyl when you replaced it... this is very important.

Also I has a lot of success vaccum bleeding the entire system when I replaced the master cyl... it gets all the air out and replaces all of the fluid in the system.

Just remember to make sure you don't run out of fluid in the master cyl when vaccum bleeding or you will suck air back in... How do I know that? lol