question for brake gurus

[rustythumb]

help! car- '36. brakes- '46-'48 w/ '39 pedals. brakes gradually lock up when they get hot after 20 minutes of driving. normal when they cool down. i have since replaced master,wheel cylinders,shoes,springs & hoses & problem is the same!any ideas? thanks! p.s.- brake lines are new & not near exhaust.

[V8COOPMAN]

Make sure that there is about 1/16" freeplay between the pedal's pushrod and the piston on the M/C. The piston absolutely MUST return completely to allow fluid pressure to return to effectively ZERO after each application. Make sure the return spring is returning the pedal all the way, also. DD

[1931 flamingo]

Ck your M/Cyl rod for being too tight to the piston, keeping some pressure on the brakes.
Paul in CT

V8COOPMAN: Great minds think alike...................

[glennpm]

In addition to the master cylinder checks, old rubber brake line hoses can prevent free flow.

[alanwoodieman]

adjust your brakes when warm, otherwise they can be set up too tight

[rotorwrench]

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There is a little return port in the bottom of the master cylinder reservoir that can get crud in it. A person may have to draw the fluid out of the reservoir to see if it is clear or not. Sometimes even with new components a little piece of rubber can get in there while fluid is returning.

[Bruce Lancaster]

I think this is well covered here...but I'd add in some more on the pedal itself.
1. return spring should return pedal to top very positively.
2. Bushings...worn out bushings and shaft can produce very eccentric pedal movement and the possibility of pedal stopping at positions other than actual top!
3. Study pedal movement from beneath car, watching as someone uses it smoothly, stomps on it hard, lets it pop up, etc.
4. Around the pedal...a flap of rubber mat or carpet around the hole can do bad things. In other words, once the free play and return are adjusted, be certain that the pedal has actually read the plan and followed along!

[FlatheadTed]

Yes at least 1/8 free play before pedal contact on the MC piston ,

[rustythumb]

found the problem! thanks to everyone for suggestions, especially bruce lancaster! when i rebuilt the brakes,i added the thick rubber pads on the pedals, [it didn't have them before]. because of that,the pedal was not returning all the way! adjusting the rod to master cylinder had no effect. this has been driving me nuts for weeks! after i cut the pad off all is good. thanks again!