The Stovebolt Site Forums The Shop Area General Truck Talk bleeding disk/drum brakes

Hi Guys,

I have exhausted my knowledge on brakes. I have a 1950 1/2 ton that I installed the POL disk conversion on the front axle. I also installed their dual master cylinder. Prior to installing the MC is did the bench bleed with the tubing fittings that came with the kit. I used the centering tool to ensure that the proportioning valve is centered with the switch removed.
The pedal goes to the floor with no pressure. I tried the one person vacuum bleeding but that has never worked for me, on any of my vehicles. I did the two person bleed, three pumps and then hold (this has always worked). I made sure the reservoir did not run dry. That did not work, the pedal still goes to the floor. My wife was doing the pressing of the pedal and she said she felt an increase of pressure when she was pumping the pedal but after closing the valve, the pedal to me did not feel like there was pressure and it still went to the floor.
Today I installed some of the Russell check valve bleeders on the rear and bled the drums by myself but the pedal still went to the floor.

The next thing I will try is the remounting the bracket of the MC. There are two sets of holes and one set will move the MC closer to the pivot but I think I have it correct per the instructions. This will shorten the stroke, I think. It is only about 1/2 of distance to the next set of hole so it is not much.

Anyone do this conversion and can tell me what I am doing wrong?? Do I have to re-bleed the MC? there seems to be zero pressure on the pedal.

thanks
skipper

Are the rear brake shoes adjusted properly? Disc pads don't retract, but the shoes do. If the shoes don't get pushed firmly against the drum all the pedal stroke gets taken up trying to get the shoes moved far enough to get some resistance to pedal movement. Some people recommend adjusting the shoes tight against the drum before bleeding, then resetting them to the proper running clearance once the bleeding is finished. On Bendix brakes the proper adjustment method is to tighten the adjuster until there's a firm drag (not locked up) on the tire and wheel assembly, then back the adjusting wheel off one turn. That's 10 clicks on a manual adjuster, or 20 if you've got self-adjusting brakes with the fine-tooth star wheel.
Jerry

If it's a power brake system, another possibility is that the adjustment rod between the booster and the master cylinder is badly out of adjustment. They make a tool to check the clearance. Should be about .020.

Mityvac Vacuum Pump makes a great friend!

Miraclepieco, has the answer. My system on the ‘62 C-10 did exactly as yours and adjusting the rod properly cured the problem.🛠

Hm, I did not check the clearance on the shoes. I set them so that they drag just a bit but I had set them prior to filling the system with brake fluid.

I system I installed does not have the power booster. It is only the MC. How much of a stroke is needed to completely compress the MC?

I tried the mityvac but it has never worked for me. I am sure I am doing it correctly but it has never worked on any vehicle of mine. I even bought one of the harbor freight compressor vacuum bleeder and it did not work.
I will check my shoe clearance tonight.
Thanks all, I let you know what i find.

All told, how much fluid are you going through? We know the fluid has to be going somewhere.
Which leads me to the next question; are there any puddles yet? Under the wheel cylinders (wheels)? How about puddles elsewhere? Like anywhere under your rig. If not. Have a look along, and inside the frame rails (channels(s)). Feel or look along the brake lines path. See if you can find any wet spots, that might indicate a leak. A rusty line only needs a tiny pin hole to be a problem. You might find a puddle inside one of your frame rails, that isn't big enough to leave a puddle under your rig.

Hope this helps.

Chris

Well, you guy were all correct. my cylinders were not actuating because they were stuck. I did rebuild them but it had been sitting a while that they got stuck. They were also leaking. I bought two new cylinders and I am replacing them but I am having some trouble installing the brake shoes. These are Huck brakes, not sure how they are different from the Bendix but I always struggle to get the single spring on the shoes. It seems the only way is to place the sharp end of the spring pliers onto the shoe lining. I have been chewing up the brake lining to have something for the pliers to grab onto. Is this correct or am I using the tool incorrectly?

I use vice grips far enough away from the hook end of the spring so that the vice grips don't interfere.

I had very good results with pressure bleeding, once I got the special cover to seal over the dual master cylinder had the brakes bled in under a half hour.

had to use to use some extra clamps to seal the bleeder cover in place.

Special brake pliers are made for this purpose, inexpensive. Or a piece of rod, bent for a handle, grind a groove very near the end, getting deeper as one goes around the rod.

Ed

As Ed suggested, brake spring pliers (and other brake tools) - make the job easier and quicker.

The correct tool as shown in the manual, uses the lining surface to pull against. That tool can make grooves and marks in the lining.

With all the posts that I have seen with problems bleeding the modified split brake system, it makes me wonder if the system would provide any braking at all when one system fails. I haven't seen a post where someone actually experienced this. I know that the split systems as they came from the factory did indeed work.

Bleed many of them but I always put a piece of material between the brake lining and the tool.

Surprised I could walk in to autozone and still get the correct MC. Had just
replaced 2 slave cylinders and MightyVac did the trick.
Clutch and brakes have more 'feel' than ever.

Some one mentioned pressure bleeding, that works good until a cap or cover leaks, then you have paint remover on everything. I much prefer vacuum bleeding, I use one of those oil suction pumps that way you have lots of capacity for the exhausted fluid.