VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 can a ruber brake hose suck air and not leak fluid

I am working on a 1940 Chevy Sedan.

I replaced the master cylinder and all 4 wheel cylinders. I bleed the brakes, but the pedal still goes to the ground. After pumping the pedal a couple times, I get a pedal. I cant find any leaks anywhere. Is it possible that the rubber hoses are sucking air but not leaking fluid?

I guess unusual things are possible but in a properly functioning brake system, there is always positive pressure.

Adjust your brakes. It's taking too much fluid to drive the shoes against the drums.

Not likely as the pedal pressure is many times greater.
I still think you have an incorrectly assembled master cylinder.

Every time my pedal get a bit too low I adjust the brake shoes and it brings the pedal back. If the shoes are too far from the drums a stroke of the pedal only get them part way to the drums. Each stroke gets them closer. A stroke of the pedal only moves so much volume of fluid. Pressure differential should have nothing to do with the volume.

The brake shoes are all new, and adjusted out to a slight drag. The master cylinder is new and I suspected it was the problem, but I rebuilt the old one and get the same results. I am running out if ideas.

When you finally get some pedal does it hold or slowly drop toward the floor?

I still think it is probably something wrong with the master cylinder. Strange if you have had 2 different ones on there but.....

Hydraulic systems are fairly simple. An essentially non-compressible fluid fills the system. When more fluid is forced in then the pressure increases or the volume in the system expands (like brake wheel cylinders moving shoes toward the drums).
Essentially only three things can be the problem. 1. Master cylinder does not force more fluid into the system. 2. The system contains something that is compressible (air). 3. The system volume changes (brake cylinders move shoes toward the drums, hoses bulge or there is a leak).

Yes, are you sure that you got all of the air bled out of the system?

Once I get a pedal, it holds tight.

I could be wrong but to me that just screams brake shoes out of adjustment, too far away from the drums. Are you the one who adjusted them or was it someone else?

It is possible for the wheel cylinders to admit air when retracting. If that is the case you should have a soft pedal.

What happens when you release a little foot pressure on the hard pedal? Does it then go to the floor? Or does it stay in the same position? If it stays in the same position then I agree with Tiny you need to double check the brake shoe adjustment. Lightly scraping may be high spots or shoes not centered or ??? Try locking each up and then backing off a bit.

Sounds like adjustment to me, been there done that. I had a few people tell me it was adjustment and when i got aggressive with my adjustment i found they were correct. You do have 2 adjustments at each wheel do you not? One for each shoe? I found the previous owner had only adjusted one shoe therefore the initial drag felt correct.

Excellent point. If he's only adjusting one side of the cylinder, the other end of the cylinder is taking all of the fluid. If you're not familiar with Huck brakes it's an easy mistake to make.