Just another drum brake question

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lazarat

Well-known member
Joined
Feb 7, 2018
Messages
657
Hi all, as stated I have an original bones 53 chevy 210 with 79 chev monte carlo or camaro drivetrain, including rear end. This would include the single master cylinder under the floor.

I have replaced all four wheel cylinders, and master cylinder, as well as all questionable brake lines, (a couple of which were rusted through and leaky).

My problem, I get in the car and the wheels will lock up, brakes are great....until I drive about a mile or so. Then the usual stand on brakes and pray it will stop or something doesn't pop.

I have bled this thing several times by myself, (bottle with hose in fluid method, I use a 2x4 to lock the pedal to the floor using the bottom of the dashboard until I can tighten up the bleeder). Same problem. Brakes great then depreciate after driving a few minutes.

I read here in the search about the cylinder not going back far enough to allow fluid backflow, but all seems well in that regard.

Another question, could air be somehow sucking back into the lines without showing a fluid leak? I have read where air can go where fluid won't show.

Any input? I am sick of bleeding these brakes. Thanx.
 
Need a little more info:

Did you bench bleed the master before you put it on?

How is the pedal after a few stops, hard or mushy, going to the floor?

You say it will lock the brakes, front, rear, or both?

Does it have air in the lines every time you bleed it?
 
Need a little more info:

Did you bench bleed the master before you put it on?

How is the pedal after a few stops, hard or mushy, going to the floor?

You say it will lock the brakes, front, rear, or both?

Does it have air in the lines every time you bleed it?

No I did not bench bleed. can I still do that without removing it?

the pedal seems a little hard, and if I push hard enough the brakes will grab to one side then the other.

The brakes at morning start will lock, at first, mostly front, and bleeding the brakes by myself is hard to determine if there is any air I just keep the master cylinder fed after three slow pumps, repeating.
 
Some of my thoughts are, Bench bleeding gets the air out of the master cylinder so when you hook it up to the brake lines you don't pump a little air into the lines, far from the bleed screws. Once you've mounted the master cylinder and lines and testdriven and bled the lines there won't be an air bubble anywhere near the master cylinder, so you don't need to bench bleed your system anymore.
You have a hard pedal, so you have no air in the lines. Mushy pedal means air in the system.
I don't know why your brakes get worse as you drive.
Maybe, if you have power brakes, your vacuum pot is faulty or hooked up wrong, or the rod from the pedal is not letting the valve in the vacuum pot come back all the way.
Maybe, the leverage ratio of your brake pedal is not right. Some of the guys on this forum will know what the correct ratio is. I would think it should be 10 to 1 or 12 to 1.
Good luck with this.
 
A hard pedal means no air in the system, that's good. But, I think you have a mismatched system, I'd bet the rear cylinders are a lot bigger than what was on the stock rear end and the smaller master can't produce enough force to move the shoes. Two ways to go about fixing that, smaller bore wheel cylinders or swap to a dual chamber master cylinder that has the proper bore for the rear brake cylinders.
 
I had a similar problem on my Essex. It was a combination of two things, the rear brakes were slightly out of adjustment and the stroke on the master was to long and the pressure was bypassing back to the reservoir through the compensation port. Just not sure if a single master has that port.
 
My problem, I get in the car and the wheels will lock up, brakes are great....until I drive about a mile or so. Then the usual stand on brakes and pray it will stop or something doesn't pop.

The very definition of brake fade. How old are the shoes and drums?

.
 
The very definition of brake fade. How old are the shoes and drums?

.

The car sat for a long time. When I did the wheel cylinders I was fighting off cobwebs. The shoes were worn but had enough meat, now you are correct, possibly glazed and just old, and I was thinking shoes and they are now in my future. I will report back.
 
Doc's right on the brake fade. Sounds like the brakes are adjusted too tight and are getting hot as you drive (self induced brake fade).
Try backing the adjustment off somewhere around 10 notches.
The bigger the wheel cylinders the better the braking force up to a point. If they're too big, the pedal will go to the floor.
Brake pedal ratios are; power brakes 6 to 1 manual brakes 7 to 1
p.s. make sure the short shoes are on the leading side of the setup and the long shoes are on the back side of the setup.
This pic is of the rear but, it's the same for the front.

rear-brakes.png
 
Thanx for the tips, reminders and suggestions.

So yesterday I did the rear brakes, because I had to wait for the front shoes to be delivered to Oreilly. That is when I realized it has been at least 20 years since I did drum brakes. The driver side took me a little longer as I struggled with those nail and spring hold downs, while juggling the self adjuster and E brake linkage, with a bad shoulder. By then all my tricks came back to me, other side took only 15 minutes.

The shoes seemed brand new, but obviously over heated, When I started investigating these brakes awhile back the self adjusting rears were definitely too tight, I backed them off all the way and then added a few clicks. (no wonder the previous owner said he thought the car was slow....)

Now the pedal has more movement but it is stopping better. Today, its the front, which are much larger than the rear. Which brings me to....

A hard pedal means no air in the system, that's good. But, I think you have a mismatched system, I'd bet the rear cylinders are a lot bigger than what was on the stock rear end and the smaller master can't produce enough force to move the shoes.

I thought about this, the rears I believe are smaller than the front, apparently the shoes are, but will see.

The passenger side still has the drum riveted to hub, I am debating having a local machine shop grind them off.

More later.
 
You want the rear drums to be smaller than the front, the front does 75% or so of the braking. I have 12" fronts and 10" rears. I didn't think about the shoes being so hard they were fading, sounds like you're on the right track now.
 
Ok so battling mosquitoes at the crack of dawn wearing one of those headband lights I attacked the front. The verdict is that what look to be at one time brand new shoes were over adjusted and got too hot.

The pedal now has more travel but stop much better, I probably need to get the back tightened up a little and maybe a notch or two on the front. Car rolls much better.

The next time I do brakes its going to be the dual MC and the front disc kit.

Thanx again, great bunch of knowledgables here:)
 

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