Right Rear wheel locks up when stopping

[clarkaw1]

My right rear wheel is locking up on wet or dirt roads. It’s a 76 with front discs and drums in the rear. I recently replaced the following: Master cylinder, power booster, stainless hoses from the proportioning valve to the calipers, new wheel cylinders and new drums in the rear and all new brakes all around. I made adjustments to this wheel in question but the problem continues. What gives?

 

[siderbox]

When you say recently, how recently?
Did it start after said repairs?
Is there any chance there's an axle seal leak?
Maybe the drum is out of round?
The other side is out of adjustment?

 

[gumbydood]

I'd say the right rear wheel cylinder is sticking on one side, causing the other side to push out twice as fast... this causes the shoe to push against the drum earlier and harder than otherwise would occur, locking the tire.

Just 'cause it's new doesn't mean it's right (unfortunately)

 

[broncnaz]

Probably just a adjustment issue or the shoes havent fully seated in both drums and one is just locking up because they have seated in that drum. There could also be some air in the wheel cylinder thats not locking up.

 

[clarkaw1]

When you say recently, how recently? Less then a month for everything (new left rear wheel cyclinder yesterday.Did it start after said repairs? YES
Is there any chance there's an axle seal leak? Doesn't appear to be
Maybe the drum is out of round? Brand new but it could be?
The other side is out of adjustment?

I adjust the brake shoes to where the drum will go on with very little fight and then using adjustment tool, tighten the shoe where it start to grab a little.

 

[Greg_B]

Just a stretch here but mine did that after I had a roll back haul it to the muffler shop... the goofball put the chain around the brake line and pinched it almost shut on one side.

Also had this happen when the real axle seal leaked out on the shoes.

When I bought it 15 years ago it almost spun me out the first time I drove it. One rear drum was warped and had a crack in it and the rear axle was bent along with the rear wheel. Evidently someone has slid the rear end into something hard and damaged it. Replacing axle, drum, shoes and new wheels corrected that.

Just a thought...

Greg

 

[clarkaw1]

OK, I installed a new wheel cylinder to the left side two/three days ago, thinking the same thing as gumbydood (maybe the left drum isn't working and the right is making up for it?). But after installing the new left W.C. the problem still exist. Today I pulled the right drum, checking for any thing that could be causing this and to readjust the shoes. After, I took it up to the car wash, all seem fine but after pulling out of the car wash and stopping at the light, the two people on their motorcycle now need to change their underware due to the loud lock up wheel sound from the 36" IROK tire. Problem not solved.

 

[Greg_B]

I am going to guess that the drum is warped or out of round or you have a bent axle shaft... If it is the left side can you look in the mirror and see if the wheel is rolling true when you are going maybe 20MPH? Thinking maybe a high spot is catching before the other side?????

Any chance the shoes do not match? Different brands? Grasping here.... If it were both sides I might say a faulty master cylinder... I went through about 5 of them before i got one that didnt leak or feel spongy.

Brake drums are fairly cheap at autozone.... I never turn mine anymore... just but new... cost isnt much different... and I dont have to worry about the brake guy screwing them up which happens to be about every other time.

Greg

 

[siderbox]

I hate to ask this, but I'm going to anyway %)

Any chance two secondary shoes on right side and the two primary shoes on the other side?

 

[DirtDonk]

Definitely check the shoe positions.

Sounds like you're going to have to dig into it again, but I would verify that both wheel cylinders have the same diameter piston. No outside difference between a 3/4" and a 15/16" as far as I know, so you could be sporting different sized cylinders.

Heard of it happening quite a bit in fact, so probably worth a double check, even though it's a hassle and means at least a partial disassembly of the brakes.

But check the drums for true first. At least that's easy and might even be free.

Good luck.

Paul

 

[gumbydood]

What I mean is that on the RIGHT REAR WHEEL CYLINDER, one of the pistons (there are 2) is stuck in, so the other one is pushing out twice as fast... this causes one shoe to be pushed into the drum before it is supposed to, leading to a lockup of this tire.

When the brake pedal is pushed, a piston is pushed down the master cylinder, forcing the brake fluid out, through the brake lines, and into the slave cylinders/calipers. This hydraulic pressure then pushes the pistons out, which forces the brake shoes/pads against the drums/rotors. All of these items are designed to be balanced: the master cylinder diameter and throw must be properly sized for the calipers and slave cylinders so that the proper amount of fluid is forced into each corner, providing equal forces upon all braking surfaces. If one piston is stuck in a 2 piston component (like one side of a rear wheel cylinder), the other piston is forced out twice as far for a given stroke of the master cylinder. This excessive movement will cause the offending piston to force its pad/shoe against the drum/rotor early.

You should be able to determine if I'm right if you remove the right rear drum and have someone step on the brake. I'd put money on either one piston sticking, or something preventing one side from moving properly.

Good luck
G'dood

 

[siderbox]

What I mean is that on the RIGHT REAR WHEEL CYLINDER, one of the pistons (there are 2) is stuck in, so the other one is pushing out twice as fast... this causes one shoe to be pushed into the drum before it is supposed to, leading to a lockup of this tire.

When the brake pedal is pushed, a piston is pushed down the master cylinder, forcing the brake fluid out, through the brake lines, and into the slave cylinders/calipers. This hydraulic pressure then pushes the pistons out, which forces the brake shoes/pads against the drums/rotors. All of these items are designed to be balanced: the master cylinder diameter and throw must be properly sized for the calipers and slave cylinders so that the proper amount of fluid is forced into each corner, providing equal forces upon all braking surfaces. If one piston is stuck in a 2 piston component (like one side of a rear wheel cylinder), the other piston is forced out twice as far for a given stroke of the master cylinder. This excessive movement will cause the offending piston to force its pad/shoe against the drum/rotor early.

You should be able to determine if I'm right if you remove the right rear drum and have someone step on the brake. I'd put money on either one piston sticking, or something preventing one side from moving properly.

Good luck
G'dood

That's not the whole story how drum brakes work.
In a self energizing drum brake system the front shoe (primary, the smaller lining) is pushed against the brake drum by the wheel cylinder.
Then the primary shoe is rotated by the drum pushing on the adjuster in to the back shoe ( secondary, the larger lining).
The secondary shoe then is rotated by the drum into the anchor point above the wheel cylinder. The secondary shoe has no were to go.
At that point the contact between the secondary shoe and the drum slow the rotation down.
This is the reason self energizing drum brakes are less effective when trying to slow down in reverse.
The primary shoe is asked to slow the drum from rotating. But it has less lining.

 

[gumbydood]

That's not really how drum brakes work.
In a self energizing drum brake system the front shoe (primary, the smaller lining) is pushed against the brake drum by the wheel cylinder.
Then the primary shoe is rotated by the drum pushing on the adjuster in to the back shoe ( secondary, the larger lining).
The secondary shoe then is rotated by the drum into the anchor point above the wheel cylinder. The secondary shoe has no were to go.
At that point the contact between the secondary shoe and the drum slow the rotation down.
This is the reason self energizing drum brakes are less effective when trying to slow down in reverse.
The primary shoe is asked to slow the drum from rotating. But it has less lining.

So there isn't 2 pistons in a rear wheel cylinder? They don't move away from each other? Every drum brake I've worked on has a wheel cylinder that pushes the top of both shoes out. The action that follows is immaterial at rest, as it's really hard to observe the self-energizing portion of the drum brake while the car is stationary. It's easy to see the piston not pushing out of the wheel cylinder.
I bring this up since I've personally seen this occur on drum brakes. A stuck piston caused premature wheel lockup... sorta like the problem the OP is having with his brakes.

 

[siderbox]

I have changed some of the wording sense your post gumbydood

There are two pistons. Yes they move away from each other. And all the other things you said.
But most of the friction is created from the wedging of the secondary shoe against drum because of the anchor pin.

Self energizing doesn't happen when the car is stationary. Nor will you have a problem with the brakes locking up.

I hope we are having a civil discussion about this to help clarkaw1 fix his Bronco.

 

[gumbydood]

I appreciate your expanding upon my brief description of a hydraulic braking system. I did not mean for anyone to believe that it was complete in its description, as there are many other components to a braking system, with entire books written on just this subject. I was merely trying to lay a basic groundwork of the function to allow understanding of my remote diagnosis, and the reasoning behind it.

Your original wording was more... aggressive than your edited post is, causing me to feel the need to defend the accuracy of my post. My intent is to assist the OP in making his bronco safe to drive.

G'dood

 

[siderbox]

Sounds good gumbydood.
After rereading my original post, I thought the same thing. I sure did not mean it that way.
I have a bad habit of coming across harsh.
When I do that my wife says "your filter's dirty"

 

[gumbydood]

No worries. With electronic media it is easy to incorrectly interpret the poster's intent.

When the OP posted he replaced the LEFT wheel cylinder based upon my post, I felt the need to be more specific on the mechanics of the failure I expect he will find. I'm just sorry I wasn't clear enough in my original post that he wasted the time, effort, and $$ on the left side.

 

[clarkaw1]

Your not wasting my time or $$, I though the left wheel cylinder needed to be replace as well. I'm trying to replace all my bake parts anyways. Thank you and to all for your help.

No worries. With electronic media it is easy to incorrectly interpret the poster's intent.

When the OP posted he replaced the LEFT wheel cylinder based upon my post, I felt the need to be more specific on the mechanics of the failure I expect he will find. I'm just sorry I wasn't clear enough in my original post that he wasted the time, effort, and $$ on the left side.

 

[clarkaw1]

Yeh, I double check this myself with my Haynes manual as well, the short shoes is in the front (closets to the doors) on both sides. I just got home so I haven't yet to reply to everyone or work on my baby but again thank you and everyone for helping.

I hate to ask this, but I'm going to anyway %)

Any chance two secondary shoes on right side and the two primary shoes on the other side?

 

[clarkaw1]

The drums are brand new and I drove it today to work, around 35 miles one way. If i had a bent axle shaft (I'm not saying I don't) but there is no shaking come from the rear at all ~ 65-70 mph. I may have my wife drive the Bronco while I follow her to see if there is any warping, as long as she doesn't fall in love with it. I replace both sides on the same night, out of the same box, but who knows if the manufacturer mix the shoes up?

I am going to guess that the drum is warped or out of round or you have a bent axle shaft... If it is the left side can you look in the mirror and see if the wheel is rolling true when you are going maybe 20MPH? Thinking maybe a high spot is catching before the other side?????

Any chance the shoes do not match? Different brands? Grasping here.... If it were both sides I might say a faulty master cylinder... I went through about 5 of them before i got one that didnt leak or feel spongy.

Brake drums are fairly cheap at autozone.... I never turn mine anymore... just but new... cost isnt much different... and I dont have to worry about the brake guy screwing them up which happens to be about every other time.

Greg