The Stovebolt Site Forums The Shop Area Driveline Brake fluid in lines not feeding back into M.C.

I have a '46 with huck brakes, but am using '53 brake pedals and associated hardware to incorporate my 235 engine. The master cylinder is a new one for 51-53 trucks. The brakes keep locking up and i have to open up one of the wheel cylinder lines to release the fluid and pressure to get the truck to roll again. Every time i step on the brake pedal, its the same thing all over again. I don't see any kinks in the line. All items on my build are new or rebuilt. Any ideas ? Cecil..........

Do you open the line or the bleeder valve at the wheel cylinder?

Do you always open the same one?

Is the pedal adjusted right, will it bring the MC plunger all the way back when the pedal is at the top of it's travel?

One way to check is see if you can wiggle the linkage at some point near the top of the pedal travel. If you can't then likely the MC plunger never fully retracts and the linkage needs to be shorter.
Hard to explain, but hope it helps,

Grigg

Other likely cause is an internally collapsed rubber flex line acting as a check valve, you can't see the problem from the outside. I have run into that before, but never on a new flex line although it could happen..

guys,
what are "huck' brakes ? how do they work, and what years were they installed ?

thanks.
leonard

I've read that the master cylinder doesn't allow the return of fluid from the brake system until it's completely retracted. If it's out of adjustment, the plunger won't let fluid back out of the system, locking the brakes. Never happened to me, but I've heard of it.

Good luck to you, I'm doing a full brake replacement on my '51 and may run into the same problem. Seems to me there is a section on adjusting the pedal free play in the shop manual.

David Bush

Huck brakes were used through 1950 - in '51 GM went to Bendix style brakes. Huck brakes have the wheel cylinder at the top of the backing plate, like Bendix, but the adjusters (there are two) are on either end of the wheel cylinder, not at the bottom like Bendix. I've got both - Huck on a '46 1/2 ton and Bendix on a '51 1/2 ton.

Just got into the Bendix system, but offhand it looks like the adjustment system is superior to Huck. With Huck you're adjusting each shoe individually, with Bendix one adjuster does both at once.

David Bush

Lonnie, i open the bleeder valve at the wheel cylinder and its doesn't make any difference which one i open. Grigg, there is a little play in the pedal, but very little. I will recheck to see if the plunger is completely retracted. Cecil.......

Huck Brakes , Bendix Brakes.
Notice the differences.

thanks much david bush and longbox55.
i learned something new today. LOL.
leonard

I have a similar problem with my rear brakes when I go on long rides or when i use the brakes a lot the pressure builds up and eventually the rear brakes won't release. Still trying to figure it out as well.

Probably the flex line at the rear axle, or at least worth looking at/replacing first.

I FINALLY now know what "huck" brakes are! Thanks!

Bill

I agree with the above posts ..check that flex line from your frame to the rearend ...that bugger cost me a days headache when I tried to bleed my new system ..it wouldnt let fluid go past it ...an THEY WILL WORK IN REVERSE ALSO ..let the fuid pass but not go back.
Tim

If it doesn't matter which bleeder valve you open, I would suspect the compensating port in the master cylinder is plugged. The compensating port is a small hole, about .020" at the bottom of a counter bored well just ahead of the larger fluid port that is the most visible port in the fluid reservoir. A fault in one of the flex lines would mainly affect one front wheel, or the two back wheels. The back wheels have a common flex line. Compensating ports tend to be ignored during brake work, because they are not very noticable.

Pedal adjustment is also a possibility, and if I remember correctly, there is a clevis that is adjustable on the push rod on the master cylinder. With insufficient piston travel upon release of the brakes, the compensating port will remain covered by the piston and the residual pressure check valve on the MC piston will retain pressure in the system. Add a little heat and you will have locked brakes that need to be released by opening a bleeder valve.

A little more on the Huck brakes: the anchor is at the bottom, and they are not "self-energizing." In the Bendix brake setup, the wheel cylinder is the anchor and the shoes are free to move slightly with drum rotation when the brakes are applied. That movement gives a "self-energizing" effect which improves braking effort without increasing pedal force. Some manufacturers, GM among them, referred to those brakes as "duo-servo" brakes.

Harvester