drums brakes building pressure while driving, help needed.

I have a 53 f100. Last year, the master cylinder, brake lines, hoses and wheel cylinders were all changed. Brakes worked great all spring. However now, they are building up pressure while driving on trips over 5 or 6 miles to the point of basically locking up. After this, if the truck sits for an hour or so, the brakes eventually leak down and you can drive it again. Any idea on what the problem/solution is?

 

Is one of the new lines run close to the exhaust? Just a guess?????

 

Do you have some free play between your pedal arm and the rod going into the master cylinder?

 

Check your M/C to see if it's overheating. If so, track down the heat source.

 

Yep. Rod going in to master cylinder is to long. Only the slightest fraction of an inch is all it takes.

 

adjust your brake pedal rod

 

If it doesn't the master cylinder piston will not come out far enough to expose the hole for the brake fluid to transfer back into the reservoir as the fluid heats up expanding and the pushing the brake shoe out against the drum.

 

First thing to do - when the brakes get to locking up, crack a bleeder to see if there is pressure (careful, the fluid WILL be hot).

If there is pressure, check next the rod into the master, make sure it is fully retracting and has free-play.

If all is good there, the relief port in the master is probably plugged. This is the least likely, so last to check.

BTW, anyone else remember that this was a subject from the Model Garage??

Cosmo

 

X3 on push rod free play adjustment

 

Yep, I'd look for a line close to your exhaust. Had the same problem on my
Nomad. Routed a new brake line to the rear of the car and routed it differently, no more problems...

 

The rod going in the Master cylinder is too long....turn it in about 3 turns or so. Problem fixed....if not...2 more turns.

This has been mentioned a time or two and also the brake pedal should have about 1/4 inch free play before the MC engages if the rod is adjusted properly.

 

Had exactly the same thing happening with my 51 Merc. Rebuilt everything and it still happened. Finally installed a NEW master cylinder and problem solved. For some reason rebuilding the old MC didn't solve problem

Les

 

Sometimes the brake hose is the culprit. It's liner will collapse and become a check valve not letting the fluid return to the master. Jim (55willys)

 

had this happen on a dual hyraulic set up ( hyd over hyd ) on a old chevy straight truck , the return spring on the pedal broke and was pumping up the system as we drove down the road as the pedal bounced back and forth

 

Yep lack of a pedal return spring can cause this issue as well.