46 Truck Brake Problem, need advice...

[deathwish]

Hello, I am new here but I have a serious issue and wanted to see if anyone can help.

I have a 46 truck, the brakes are stock except the previous owner changed the front drums to late 70's chevy truck disks. I have plenty of play at the master cylinder and the rear ford drums are working well. The issue is that if I drive for a prolonged amount of mileage, 20 or so miles, the front disks begin to self clamp, as if I was playing with the pedal. The pedal itself begins to lose its play that it has at rest till the truck wont roll at all. The rear drums are cool but the front disks are understandably hot. Now it will do this but if I then park the truck and let it rest everything returns to normal.

Can someone help me out? Thanks again, Roger

 

[Kurt in NJ]

What was used for a master cylinder?
A drum brake system has a residual pressure valve that keeps a little pressure in the system, many disc brake systems have a valve that prevents pressure from reaching the calipers until it rises above a low threshold.

Most drum brake systems needs the small amout of pressure to help keep the wheel cylinder cups tight to the cylinder to prevent them from leaking, but some systems (most modern disc/drum) also use expanders that use the spring to force the cups tight to the cylinder so a disc brake master cylinder can be used.

Whenever we do a modification to our old Fords other modifications will need to be done in most cases to make the first modification work properly.

 

[deathwish]

To my knowledge it is a stock master cylinder that is still being used, I included photos as my knowledge of stock parts is not the best. Thanks, I hope this can lead me in the right direction.