The Stovebolt Site Forums The Shop Area Driveline Brake Master Cylinder, 1949, 3100, pickup

Saw in my brake problem search that someone suggested "bench bleeding" the master cylinder before install.I filled my new cylinder, installed and I still can only pump up the pedal then it looses it and the pedal goes to the floor even after bleeding. That's what the old one did and I thought it was because the pits in the cylinder.I have no line leaks and the wheel cylinders are adjusted pretty close. Do I have a bad master cylinder or have I done something wrong?

So, Did you "bench bleed" the new master cylinder?

Unless you have a newer style master cylinder there is no need to bench bleed the stock AD master cylinder. When you say new, do you mean "New"? Are you sure your keeping the fluid level up to the top in the master cylinder? You may have to refill it a half dozen or more times to get all the air out of the lines, and make sure your not running it dry or you will just pump more air into the lines and be starting all over again. Who is helping you bleed the lines? are you sure your following the proper bleeding procedure?
Denny Graham
Sandwich, IL

...sounds like there just has to be a lot of air in the system. When you bled the system are you following proper procedures? Pump the pedal, open the bleeder valve, close bleeder valve and THEN let the pedal back up.
Are you getting Fluid at the bleeder valve? Are you getting Air out of the bleeder valve?

Need some more info to help..... and you say there is no leaks but beware that sometimes the lines can leak and the fluid run along the chassis rail and not instantly show up.

No need to bench bleed? Why not? Why not start with a M/C with no air in it?

Make sure all the shoes are adjusted right. Those old Hucks are hard to adjust. Each shoe has an adjustment. All of the adjustments are right hand threads. If you have worked on the brakes you know how they are constucted & you can visualize in your mind which way to turn the adjustment. Even if you adjust them up till they lock up or are real tight you can get a good pedal & then go back & adjust them properly. Usually about 4 notches back from a heavy drag is about right. You may still have a little drag but that is OK. When you get them right the pedal will hardly go down. You just apply pressure to it. Make sure your master cyl. push rod is adjusted to let the piston go all the way back. If you are haveing trouble bleeding, speedy bleeders might help.

As others have said, I'd bet you don't have the shoes adjusted correctly. All the fluid is filling the slave cylinders before they engage the drum. Tighten them up till the wheel won't turn, then back them off a little at a time.

Also, you might consider a 10lb residual pressure valve between your MC and brake lines. This will maintain 10 pounds of pressure in the line which should prevent the slave cylinder from totally emptying between uses even if your shoes aren't adjusted just right.