Hi All,

I am afraid that I am at the end of my rope & am ready to give up. Being a manly kind of man, I have put off asking for help as long as I could! LOL

I have a 55 F-100 with stock brakes - drums all around & a stock master cylinder. The only non-stock items are automatic brake adjusters, I installed them in the midst of doing all the following listed repairs items. I did not have this problem before installing the auto adjusters. (But I don't think that they are the problem, they adjust well & don't over or under adjust.) I verified that I have them properly installed - I looked at my '78 truck & used it as a check against my '55 install.

My problem: with use, the brakes will "pump up" over a short period of time (maybe 45 minutes), until all brake pedal movement is gone & the brakes are fully engaged even without me touching the pedal. If I let her set about 1 hour (if I do it before or after all pedal movement is gone), the pedal will go back to her starting position. I can also loosen a bleed valve & will get a small amount of fluid go out & can hear the brake pedal go back to it's start position. I believe that the wheel cylinders are not returning to their original positions & eventually brake drag occurs, resulting in total lock-up.

What I have done to date:
Replaced all 4 wheel cylinders, found 2 leaking.
Replaced all 3 brake hoses (found 1 that was partially blocked & didn't allow fluid to return to the master cylinder fast enough).
Rebuilt the master cylinder 2 times (the 2'nd time because I figured that the check valve was not allowing fluid back to the master cylinder resevoir fast enough - took about 10 minutes for the pressure to fade & the brake lights to go off before the 2'nd rebuild). The brake light now goes off immediately after releasing the brakes now.
Replaced 1 leaking steel brake line, other 4 lines have no kinks in them.
Replaced all brake pads & drums.
Replaced the brake switch.
I have the cleanest brake fluid ever seen, I've gone through about a quart of fluid doing all the repairs listed above.

Over the 3 week repair period, my brakes went from spongy to nice & firm. I, in my infinite wisdom, didn't do all the repairs at once, I was eliminating the obvious problems & eventually ended up replacing everything. I replaced all wheel cylinders when I found 2 leaking, then I had front passenger brake drag until I figured out that the hose was bad, then I had drag all around until I figured out that the master cylinder check valve (after rebuild #1) was too restrictive. Both times I rebuilt it I used a Raybestos kit.

Any thoughts?

Thanks & Regards,
Jon

 

You are not alone! I have been down the very same road with my f600. All wheel cylinders, rebuilt master, etc. After many frustrating attempts at fixes, I talked to a truck mechanic. Between your brake pedal and the master cylinder there should be an adjustment rod. Back it off (shorten the length) 1/2 to 1 turn. That will back the brakes off. You will also notice your brake pedal travels farther now. If it is to much for your liking you can turn the adjuster(lengthen the rod) 1/8 turn at a time. Adjust, then go for test drive. Continue until satisfied. I know the frustration. I had to get out of my truck, crawl underneath and back off rod at stoplight so the &^%* truck would move when light turned green. This is very hard on brake linings and tempers. Hope this helps.

 

56f600 has the right fix for your brake problems. You have to have some play in the brake pedal adjustment. The rod into the master cylinder has to fully return to the end of it's travel or the fluid will not return to the reservior. Turn the adjuster until you can feel some play in the pedal. ...Terry

 

Back Again,
Thanks 56f600 & Overkill-F1 for your replies!!! Well, after I quit last night in disgust, the brake pedal was pretty close to having no play in it. This morning it was back at it's starting point again, with lots of play. I took your advice & backed the master cylinder linkage off some more, it's a lot closer to the floor than I would like. However, that said, there is still plenty of stopping power left. I did come up with another thought - I had the mastercylinder filled pretty full. So I got to thinking that maybe it needs a pocket of air in it to properly work. I took some out & went on a road trip. Brakes seemed OK, I couldn't tell if they were pumping up or not. I'll find out tomorrow when I drive my 65 miles to & from work.
Thanks & Regards,
Jon

 

I got Brakes that work!!!!!!! Man Oh Man do I feel stupid. I had overfilled the resevoir & when the brakes heated up, there was no room for expansion. I see from another brake post that there is a vent hole, gonna take a look & see if mine is clogged. Thermal expansion, who would have thought!!!!!

 

The return hole on my Hudson is on the bottom of the reservoir. It was rusty enough I had to use a tiny drill. I'll never forget the lesson, though. I tried adding clearance in the linkage, new wheel cylinders etc. Another Hudson mechanic let me in on the secret.

Tom

 

Bruhahahahahahaha I GOT BRAKES!!!!!!!!!!!!!!!!!!! Sure enough, there are 2 vent holes on the cap. Used a No. 54 drill to get all of the accumulated crud out of them, topped off the master cylinder & I have perfectly working brakes now. Many Thanks For All of Your Help!!!!!!!!!!!!!
Regards,
Jon