Technical 1951 cadillac brake issues

Vehicle:

1951 Cadillac, OEM stock drums up front, 1989 Chevrolet, 10 bolt rear end with OEM Chevrolet drum brakes (self-adjusting). Master cylinder, booster and pedal ***embly from 2001 Camaro.


Problem:

When car is started and idling the brake pedal feels fine and brakes work great. Drive the car for 5-10 miles and rear drums lock up and brake pedal is solid. All new brake components including springs, wheel cylinders, drums, shoes, self-adjusting ***embly. All new rear brake lines and brand-new center rubber hose. Front brakes are a non-issue although they are part of the entire system.


I am out of ideas. I have made sure all brake lines are 5-6 inches away from any heat source. I am using DOT 4 fluid. Brake lines coming from master cylinder in engine bay are heat wrapped insulated. Front brakes have 10psi residual valve installed directly after the master cylinder.


Any help would be appreciated.

 

Is your master cylinder under the floor or on the firewall (above or below the wheel cylinders)?

 

Firewall mounted

 

There went that idea. You running residual valves on the back or a stand off valve?

 

No residual valve on rear as I was told that any master cylinder produced after 1981 would not need because the wheel cylinders have cup expanders built in. (Mark with ECI hotrod brakes).

 

Check the clearances between the master and booster and the pedal rod to booster.

Chris

 

It doesn't need them when the master is higher than the wheel cylinders. I was just crossing that off the list.

 

what do you do to get them freed up? lose a line? wait?

 

s pen

You should be able to reach down with your hand and move the brake pedal 1/8 inch or so before you feel the pushrod contact the piston in the master cylinder.
What happens if the push rod is tight against the piston or pushing it in just a bit the back cup or the edge of the piston covers up the port to the reservoir and doesn't allow the fluid to return to the Reservoir.


That is the common cause of that issue especially if you can open a bleeder on a rear wheel and let some fluid out and the brakes work.

As far as residual or check valves every drum brake dual master cylinder I have seen or disk/drum has a check valve on the drum brake sides that is behind the seat for the flared brake line. in the master cylinder.
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