The Stovebolt Site Forums The Shop Area Driveline Bleeding brakes, no pressure

Hello friends,

I replaced the wheel cylinders on my 1950 chevy 3100. I haven't bled brakes for eons but I remember the basics (with a YT refresher of course). I've done all four sides multiple times having someone pump the brakes for me. I also used the method where you immerse the end of the hose into a bottle of brake fluid and I had someone gently push the pedal and release, with the nipple open. using this method when the pedal is released should i see fluid getting sucked from the bottle back into the wheel cylinder? I saw no such movement. The pressure has only slightly improved; the pedal goes to within an inch of the floor.

What am i doing wrong and what should i do now? Do i need to bleed the master cylinder; is that a thing on the old ones. It has just a single chamber.

PS I'm not seeing any leaks anywhere.

Any advice appreciated.

I installed 4 new wheel cylinders on Ol' Roy a few years ago. I had the entire truck on jack stands and let gravity do most of the work.

I opened all bleeders at the same time and let the fluid flow through, making sure to keep the reservoir full.

After suitable amount of time, I closed everything up and did the standard two-man brake bleed starting with the furthest one (RR) and working to the closest (LF).

I installed a master cylinder as well. I like to bench bleed them prior to installation.

When doing your two-man bleed, make sure your helper has a clear understanding of when to push and when to release so as not to draw air back into the system. Work out a system where he repeats your order of "push" after he has pushed the pedal and then repeats released or up or whatever after you tell him to release the pedal.

This way both of you know where the pedal is supposed to be and where it actually is.

Make sure your brake shoes are all adjusted according to spec.

thanks for the tips; I mostly followed the process you outlined. i tried the gravity bleed too but couldn't get any fluid or air to come out. should i not tighten the lid on the master cylinder. I just thought of that, maybe it couldn't flow due to the lid.

When I've done gravity bleeds in the past I could never get that solid pedal feel. I always use a helper and like Otto mentioned, make sure both of you are on the same page with Push and Release. And don't forget to check the master cylinder and not let it run out of brake fluid.

Normally you leave the lid off/loose so you can monitor the fluid level and keep adding fluid when required.

And just to reiterate that the shoes should be adjusted to spec when doing this.

If your helper is letting the brake pedal come back up before you have closed the bleeder, air will be pulled into the system. Have helper pump brake pedal three times, then push pedal down while you open bleeder. Then close bleeder before the pedal is allowed to come back up. Repeat as needed. Also follow the correct wheel sequence; longest brake line from master cylinder first, finish with shortest line.

Che, I've always had good luck with suctioning the old fluid from the master cylinder and filling with new, a clear tube in a bottle of old brake fluid, open the bleeder on the R/R (only) and pump away until clean fluid comes out. As mentioned the shoes should be adjusted first. Air can't enter when the pedal is released since it'll just suck in brake fluid.

Some good advice above, Good Luck.

RonR

1950 had Huck brakes. There are two adjusting wheels for each wheel cylinder.
I have found that the best way to deal with the difficulty of bleeding that style of brakes is to adjust both adjuster wheels on each wheel cylinder until you can barely rotate the tire. This will take all of the slack out of the brakes which makes it so that less brake fluid is required for the pushing the shoes into engagement with the drums.
Without tightly adjusted brakes, the master cylinder piston runs out of fluid before fluid fills the empty wheel cylinder.
Once you finish bleeding the brakes and have a hard pedal, back off each wheel cylinder adjusting wheels until the tires can turn with little effort.
Once you have driven if for a while, the shoes will wear until they match the arc of the drums and they will spin freely.
You won't read this method in any manual, but it works like a champ.

Thanks everyone for the tips, i really appreciate it. I'll keep trying.

I'm still having no luck. I noticed today that there is some leakage around the front boot on the master. I'm thinking that may be my problem and I'm wondering if that's why the brakes failed in the first place. So I see that classic parts has two options, a rebuild kit and a new master. Have folks had good luck with a rebuild kit, or should I just get the new master? Thanks.

Hard to tell without taking it apart ,if it is not to rusty a kit will work .I see Napa may have the parts still .

che - It's fairly easy to remove and disassemble your master cylinder to check the internal cylinder wall condition. If it's not pitted its worth ordering a rebuild kit, but should also include a light bore cleanup with a cylinder hone to remove any buildup/debris so the new kit will seal properly.

If the cylinder wall is pitted, you're looking at either sending it off for sleeving and rebuild or ordering a replacement. If you are on a budget, you can get a new master cylinder for your 1950 3100 from Rock Auto # 35571075 for 1/2 the cost Classic charges. Only real difference is the Classic cylinder comes with an original style metal vented fill cap, while the Rock Auto part has a plastic vented fill cap. You can always take your existing metal fill cap and transfer it to the Rock Auto cylinder if you prefer a more original look.

I installed the Dynamic Friction master cylinder from Rock Auto 3 years ago January and saved the original for rebuilding later. I needed to get the truck on the road and the new mc was only $40. It isn't as nice as the original in terms of finish but it's still working fine.

The original metal cap cannot be installed on the new cylinder because the caps are different sizes. Be careful not to cross thread the plastic cap.

Thanks very much for those quick replies. And thanks for letting me know about Rock Auto; i had never heard of them before. I went ahead and bought the one from there. Last question, do i need to bleed the master before installing it. I have the shop manual and it doesn't mention bleeding.

I always bench bleed master cylinders before installing them on any car.

Inspect the new mc carefully. As usual it's from China and not made to the high standards of the original. I had to remove a couple pieces of flash from the reservoir and "clean up" some rough finish before installation.

Despite that, I haven't had any problems with it in 3 years.

Good to know. Thanks Otto.

You didn't make any reference to having replaced the flexible brake hoses.
They can collapse with age and restrict or prevent the fluid flow.
Most of the aftermarket sources carry them.
Fred

I did the bottle bleeding with my trucks. One person. Pulled myself under the truck and depressed the brake pedal until the bubbles were gone.
Moved to the next in series. Did that twice. No problem.

to edit. thats the clear tubing going into a clear bottle with clean brake fluid. Tubing in there where no air can return to the bleeder.
My shoes were not adjusted. Making sure the master cyln does not run out. Pulling the brake pedal underneath as to pump it.
Longer the system can sit full, the better. I adjusted the shoes to where I could just hear the pads rubbing. Everything being brand new helps.

Since Bendix brake shoes free-float on the pivot pin at the top, it's important to adjust them to get a firm drag (not locked up) and then back the adjuster wheel off one turn. That's 10 clicks of a manual adjuster, or 20 with the self adjuster with finer teeth. Just "adjust until you hear a drag" doesn't guarantee that both shoes are in contact with the drum.
Jerry

Most likely. I just reported what worked for me w/o assistance. They work fine 4 years later.