rear brakes locking up-ok after cool down? 47 ford

M

mainiac239

Member
working on a 47 1.5 ton ford "big truck"
put NOS shoes on rear and shaped for correct clearance
wheels spun freely, went out for short drive on local roads (15 miles +/-)
on return brakes felt as if dragging, parked truck noticed that brake lights stayed on, about 45 min later brake lights off and wheels free again

thanks for any ideas of what to look at next
 
Check the clearance of the push rod for the Master Cylinder. You need a little or when things get warm, the M.C. Piston will not fully retract allowing the brakes to fully release.

Also, the tiny bleed back hole in the bottom of the M.C. Reservoir may be plugged up also causing the brakes not to fully release.

An easy way to check if it is a problem in the M.C. Area is, when this happens, to just crack open one of the brake bleeder screws just a little and see if some fluid comes out and the brake light goes out.

Let us know what you find.

Chris
 
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Had the same problem with our 47 PU. Rebuilt the MC with no improvement. Finally replaced the MC with a NOS one and no more problems.

Les Bliss
 
swaped out mc with new unit, bled the system
pedal not as high, but still plenty there
prob have to wait til the 4th to try it out
 
There is a tiny vent hole in the MC cap that is usually plugged up with dirt and/or grease. That, and a plugged relief port are the most common problems. The push rod needs 1/8 inch or more play to keep the piston from covering the port when hot. I earned a living for 15 years with one of these trucks. Tough old beasts that will beat you black and blue at high speed and long distances.
 
1/16" clearance between the pushrod and bottom of the MC piston bore for the pushrod will provide about 3/8" free PEDAL travel before the brakes start to engage, which is within the range that Ford specified in the 1939 Service Bulletins. An extra 1/16" will do no good at the MC, but will "waste" another 3/8" of effective pedal travel and braking... BUT 1/8" is way better than NONE or even pre-load, which would cause the problem of brakes locking when hot for the reasons already posted.
 
i had same problem it was the intermediate hose at rear it collapsed in the inside wouldnt let the fluid come bake until it sat for a while
 
Also check all hose guides or clamps for rust on inside of clamp or guide.The mc will push the fluid by the restriction but will not let it back fast enough.But my first place to look would be the clearance on mc push rod. my 2 cents lee34
 
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