1941 Ford Big Truck Brake Bleed

U

Upstate gearhead

Junior Member
I've converted my 3 1/2 ton to dual master. One line goes from the back reservoir to the rear and splits on the rear end housing. The front reservoir goes down to a dual tee for the brake light switch and the two front wheel cylinders. If I block of the two lines going to the front cylinders (past the tee), I get a solid pedal. With one or both front cylinders connected the pedal is soft. I get no air when bleeding either front cylinder. If I push the pedal down so that it contacts the master, I can pump up pressure, but as soon as the pedal goes up the last half inch, the pedal goes back to being soft (about 8 lbs push). There is no sign of either front wheel cylinder leaking.
Any idea what is going on?
 
Does the master cylinder have residual pressure valves and did you bench
bleed it before you installed it??

Bob
 
I put a residual valve on the line going to the rear. I bled the master cylinder, but was concerned that air might have gotten back in when I blocked/unblocked the front cylinders. I put pressure on the cylinder and loosened the brake line at the master cylinder to try and remove any air that might have snuck in. The master is solid with the fron lines capped off at the hose connection.
 
After installing a dual master cylinder, I experienced similar problems.
I installed 'Speed bleeders' and that cured all the problems.
Don't know why or how but they worked.
This may or may not work for you but it may be worth a shot.
 
Problem solved and it just goes to show when you have a hammer, everything looks like a nail. Not all soft pedal issues are caused by air in the brake line. In my case, the wheel cylinder cups were installed backwards. Why this had the impact it did, I don't know. Turning them around gave me brakes.
 
Just for conversation; On my 1 1/2 ton I found that the bled nipples were sucking air around the threads! Had to teflon tape the bled nipple threads. Newc
 
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