The Stovebolt Site Forums The Parking Lot Big Bolts 1946 COE brake problems ?

Hi All,
I am unable to get the brake system / pedal to be like I think it should be. The brakes engage about half way on the pedal travel...and if pumped they will come up. I have replaced the master cylinder with a NEW one, I have the Hydravac brake unit rebuilt by a reputable company, I installed a one way valve between the intake manifold and the Hydravac unit. I replaced the brake linings, I did install a rebuilt 2 ton rear end from a 1980 Chevy truck with two wheel cylinders per axle. Pedal is not spongy...just begins half way down. I have adjusted the front and rear brakes as tight as I can...several time. These are hydraulic brakes. Help...I have run out of ideas...anyone have any other ideas?
Thanks
Brian

Hy repguy, If my memory is correct, a stock 46 braking system had only one wheel cylinder per wheel. The increased volume of the two extra wheel cylinders on the rear axle may account for the increased travel of the pedal. Just a thought.

Thanks for you reply....and that may me be it. Any way to fix that besides replacing the rear end?

Are you sure you got ALL the air out of the brake lines? I was taught to bleed the farthest brake from the MC first, then the next closest, then the next,etc. I have even had to "bleed" the MC by loosening the lines where they come out of it. Just a suggestion, but it sounds like there is still air in the system.

Thanks 54tow.....I did follow the bleeding starting at the farthest away but I did not bleed the master....I did go through about a gallon of brake fluid. Thanks for the suggestion...any others?

Nice trucks, by the way. Just saw the COE, and it has that certain "something". Then I saw the 42 - my jaw dropped. I salute you!

Hy repguy, I checked some books, and your master cylinder should be a 1 1/4" bore. That same size bore master cylinder was used in the early fifties, with a rear axle with two 1 1/2" bore wheel cylinders on each side, so the capacity should be there. Did you bleed your hydrovac, I seem to remember the procedure was to bleed the hydrovac first, the upper screw and then the one on the barrel, then on to the wheel cylinders as was described, longest line to shortest line, hope that helps.

Thanks for the replies....I did not bleed the Hydrovac....did not know I was supposed to. Some further research shows that my master cylinder is below the height of the wheel cylinders and may need to have 10 psi residual press valves to keep the fluid from siphoning back to the master. I will address all of these this week.
Again Thanks to all.
Brian

Hy repguy, drum brake master cylinders have the residual pressure valve built into their components, so there should be no need to add more, hope that helps.