1956 Chev. brake problems.

Ronnie Moore
1/9/08

newly rebuilt 56. I have disk front,drum rear.Sometimes the brake petal goes to the floor.I can pump one time and have a full petal.I have replaced the master cylinder 3 times. Anyone have any ideas?

CHEVY DUDE
1/9/08

It sounds like you have air in the brake lines. You need to bench bleed the dual master cylinder before installing it in the car, then you need to bleed the entire brake system starting with the longest line and work your way up to the shortest line. You said you have disc brakes up front with drum brakes at the rear, did you install a proportioning valve in the system?

ronnie
1/10/08

Thanks dude, I bench bleed the master cylinder & have bleed the brake system several times.I don't think it's an air problem. I did not install a proportioning valve.I have thought about installing a prop. valve or residual check valve.

CHEVY DUDE
1/10/08

Ronnie, you really need to install a proportioning valve in a disc/drum combination, also have you checked the brake rod travel length with the new master cylinder compared to the original?

mike
1/10/08

If you have a single master you need to change to a dual. If you already have a dual, then the only thing that could be wrong as you describe it is the internal valving in the master. I suggest flushing the system and installing a new dual master.

Ronnie
1/10/08

I have checked the rod length.It's right. Remember this is a sometime problem. the car is not a daily driver. I have driven roughly 400 mi the past year, and the brakes failed 5 or 6 times. I think I'll try a proportioning valve, but I don't understand how this will keep the brakes from going to the floor.

mike
1/11/08

IT WONT! Pedal to the floor with no sign of leak is an internal master valve problem. Master valve opens on the return stroke. If it sticks open, the pedal will go to the floor as the fluid bypasses the piston. Your fluid is contaminated and gumming up the valves. Just a flush might help.

CHEVY DUDE
1/11/08

Ronnie, the proportioning valve is installed in a disc/drum combination to regulate the pressure between the front and rear brakes. Rule of thumb is 70/30 front to rear since the front brakes will provide most of the stopping power. Without a proportioning valve it is not unusual for the rear brakes to completely lock up. As to the pedal fade you are losing pressure somewhere in the system.
If the problem continue you may want to take it to a brake shop and have it checked out, after all it only takes one failure to lose your car or worse. Good luck.

57 belair
1/11/08

You want the air pushed away from the master cylinder. So its my understanding that the first line bled should be the shortest line since its the closest to the master cylinder. then in order until you bleed the longest line. I think you might be bleeding too much at a time and not having enough brake fluid in the master cylinder. good luck

CHEVY DUDE
1/12/08

fluid level must be monitored at all times when bleeding the lines, thats why you should have another person adding fluid as nessary when bleeding the lines.

s m
1/13/08

if in doubt about proper bleeding, just have it pressure bled in a shop.

ASE tech.
1/13/08

also, have you been monitoring the brake fluid levels while driving?check the fluid level after the next episode. any external leaks? also check the condition of ther vacuum booster, it could be working only intermittenly giving you the idea of excessive pedal travel at time. bottom line…what does the primary visual brake inspection show?

bink
1/13/08

get a new master cylinder

larry
1/13/08

blead the farthest or longest line first if you read your shop manual it will teach you a lot motors is the best

57 belair
2/13/08

was the problem with the brakes fixed?

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