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drum brake symptom

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NutmegCT

NutmegCT

Great Pumpkin
Bronze
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1958 drum brakes all four wheels. All brakes apply and release *except* for one shoe on one front brake.

Front left wheel: trailing (lower) shoe will return to the rest position if I pound it with my fist. I can wiggle it back and forth by prying with a screw driver.

But press the brake pedal, the lower shoe goes out to the drum ... and stays there.

Remove drum, pound with fist, goes back to rest position.

All lines, hoses, and shoes and return springs are new. Self-adjuster is correctly adjusted per spec.

Is this "one sticking shoe" a symptom of a failing wheel cylinder? Since all other shoes and wheels work correctly, is there some other angle I'm missing here? I don't really know how to test a wheel cylinder. :wall:

Thanks.
Tom
 
If this is the only one, you can rule out the check valve in the master. You might inspect the backing plate for burrs, etc. I use a very small amount of anti-sieze on the backing plate where the brake shoe makes contact. It maybe the wheel cylinder, but usually they work or they leak. You could pull the dust boot off and have a look at the bore?
Cheers,
D.
 
First rule of automotive repair states:

Just because it's a new part doesn't mean it's a good part.

Once you understand that, look at it like you're starting from scratch on the brake job.

FIRST thing I would do is open the bleeder when the problem occurs.
If the fluid goes "poof!" and the brakes release, it's either the hose or a smashed steel line, or possibly debris in the line somewhere.

I would look for the port in the wheel cylinder to be open and clear.

Your "wiggling" of the shoes with a screwdriver seems, to me, to rule out the problem of a groove worn in the backing plate causing the shoes to hang up, but could be.

You said all new, but didn't mention wheel cylinders.
No "poof!" of fluid would indicate wheel cylinder.
The pistons wear, and can "cock" at an angle inside the bore.

Dave
 
Thanks gents.

M/C is new also. But the front wheel cylinders aren't new; they were replaced about three years ago. Rear wheel cylinders are all new.

If there's a "stuck" piston in a cylinder, would that allow the shoe to return to rest position when I hit the shoe with my fist?

I'll give that wheel line "spurt" test a try.

Thanks.
Tom
 
Yeah, could, so could a flap of rubber in the hose.
Just do the checks, it will eliminate what it isn't, and narrow down what it is.

If the shoes lift away from the backing plate enough to clear the support pads, and they still don't retract, you can eliminate worn/grooved backing plate pads, and Lord knows I've seen enough of those!

That leaves the wheel cylinder.

Now, call me a cheapskate, if you want, but I just call it "experienced", if there is a problem, I don't want to just throw parts and money at it until it (hopefully) goes away.

I want to FIND what is causing the problem, and fix what needs to be fixed.


Dave
(oh, and on brakes.....never do one side. ALWAYS do both, meaning if one hose is bad, do both, if one return spring is bad, do them on both wheels, if one wheel cylinder is bad, do them both.)
 
You are spot on. Always do both sides. Use a clear hose over the nipple and place the end in a clean clear jar. Open the bleeder and see what you get. If there is debris present, it will be easy to see in the jar. Be sure that the shoe is not jumping over onto the edge of the support pad.
Cheers,
D.
 
Results:

Engine off, applied and released brakes.

Wheel wasn't locked, but was very hard to rotate.

Removed wheel and drum. Opened bleeder; a big drip, but that was it. Wheel now free.

Replaced drum. Engine on, applied and released brakes. Wheel very tight - tighter than with engine off.

Removed wheel and drum. Opened bleeder. A good healthy squirt. Wheel now free.

Seems the power brakes make the problem worse. But with no power brakes, there's hardly any residual fluid pressure at the bleeder.

Does this sound like a cylinder problem? At first I thought it might be the power brake slave cylinder, but the problem only happens on that one front wheel cylinder; the other wheels remain free and loose even when the power brakes are used.

Tom
 
First thing that popped to my mind was weak return springs. The spring doesn't have enough pull on it to overcome the drag and brake fluid pressure. Something to think about.
grin.gif
 
Does the vehicle have a brake proportioning valve? I would look there. What sort of fluid are you using? Have you turned all drums and arced the shoes?
Cheers,
D.
 
Return springs new and correct.

No proportioning valve, and it's a "single line" system to boot. Using DOT 4 fluid. Drums and shoes turned and arced. I'm still thinking it's a wheel cylinder problem, as the other shoe on the same wheel works fine, as do all the other wheels' brakes.

Remember, the problem shoe actually needs "convincing" to move back from the drum, tho' the other shoe on the same wheel returns freely.

Tom
 
If you get a big squirt, and the wheel rolls free, most likely hose or smashed steel line somewhere.
Springs, no, as if it squirts it out with the bleeder open, it would return the fluid uphill.
Power brakes, yes, more pressure (that's what they do), and harder lock, bigger squirt.

Now, follow the steel line up to the next junction point and repeat.
If it squirts there, well, something in the block.
I think you will find it won't squirt.
You might just try the line connection to the other end of the hose first.

If it squirts, go further up, if it doesn't, the problem is inside that hose.
 
And you are absolutely certain none of the other wheels lock up, or drag, which changes when you crack the bleeder in question?

Dave
 
TOC said:
And you are absolutely certain none of the other wheels lock up, or drag, which changes when you crack the bleeder in question?

Dave
Click to expand...

Yep - I lifted each wheel and checked. All other wheels completely free and turn easily. So no change when that front left is bled.

Another interesting aspect: there's a single rubber brake line and hose leading to each wheel brake. But on the front left wheel, only the lower (trailing) shoe sticks - not both shoes.

T.
 
NutmegCT said:
TOC said:
And you are absolutely certain none of the other wheels lock up, or drag, which changes when you crack the bleeder in question?

Dave
Click to expand...

Yep - I lifted each wheel and checked. All other wheels completely free and turn easily. So no change when that front left is bled.

Another interesting aspect: there's a single rubber brake line and hose leading to each wheel brake. But on the front left wheel, only the lower (trailing) shoe sticks - not both shoes.

T.
Click to expand...

can you swap the spring with another shoe to see if that makes a difference?
 
Odd.
But, if only one sticks, and the other retracts, can't be the hose.

This is why you A) ask questions and B) go through logical troubleshooting.

Now, since the w/cyls weren't replaced, and only one shoe is sticking (how did we determine only one shoe sticking?), replace the w/cyls.


Wait a minute-----is this car German?

Is it one of those oddballs with two single-end w/cyls per wheel with a steel line linking them?

Here I thought we were talking LBC's, in the worng forum, then I saw your 1958 Mercedes.
 
TOC said:
It IS!

https://info.rockauto.com/getimage/...ttp://info.rockauto.com/Raybestos/WK264-1.jpg

THAT makes all the difference in the world as far as troubleshooting goes.

If it's two single-end w/cyls per side, and one hangs up, it's probably the lower, or the jumper line is plugged with garbage from the old hose.
If you can get the line out, flush it out both ways with Brakleen, re-bleed.
Click to expand...

Hi - sorry but I'm dense. What's the "it is!" and the rebuild kit link for?

OK, I'm guessing you're saying I need to rebuild the cylinder using the kit?

Must be that I wasn't clear earlier. There are two shoes and two cylinders on each front wheel. On the left front, the top shoe (leading) works fine; doesn't get stuck in the extended position. The lower shoe (trailing) is the one that gets stuck. That's why I thought it was the lower shoe's wheel cylinder.

Here's a link to some helpful pictures and diagrams of the front brake system:

https://mbzponton.org/valueadded/maintenance/brakes.htm

So ... is my next step rebuilding/replacing the lower shoe wheel cylinder? Or just flushing the line that connects the two cylinders? If the latter, would I accomplish the same thing by opening the bleeder and flushing the wheel that way?

Thanks. Your expertise is *very* much appreciated!

Tom
 
By all means try bleeding the lower cylinder first, Tom. But IMO you're going to end up replacing it. Most likely the moisture in the system over time settled in the lower areas of the system... which means the OTHER side is likely to be the same.

...just sayin'.
 
Tom.
Let me re-quote from the next-to-last and last posting I had:

"Wait a minute-----is this car German?

Is it one of those oddballs with two single-end w/cyls per wheel with a steel line linking them?"


"It IS!

https://info.rockauto.com/getimage/...ttp://info.rockauto.com/Raybestos/WK264-1.jpg

THAT makes all the difference in the world as far as troubleshooting goes.

If it's two single-end w/cyls per side, and one hangs up, it's probably the lower, or the jumper line is plugged with garbage from the old hose.
If you can get the line out, flush it out both ways with Brakleen, re-bleed."


When I did a quick check on wheel cylinder kits for one of them old Mercedes, it shows one cup and one boot.
THAT is a single-ended w/cyl (see: IT IS!) and you can have damaged steel line between cylinders, debris of any kind in that line or jammed up against the end of it.
You really need to pull the steel line, and clean it out, plus the pockets for the line in the wheel cylinders.

The hose should come in lower than the bleeder, which means lowest cyliners, bleeder on highest (but, I may be remembering Dodges).

Before you go spending a lot of money on parts, just see if you can clean any of the garbage out.
Especially if the w/cyls were replaced three years ago, which is what I think you are saying.


Question:

To make certain, the locking shoe is the one where in relationship to the bleeder screw?
The toe of the shoe fits into the piston of the w/cyl, so which w/cyl is affecting the locking shoe, the hosed one or the bleeder one?

Dave
 
Hi Dave - thanks for the follow up.

"To make certain, the locking shoe is the one where in relationship to the bleeder screw?
The toe of the shoe fits into the piston of the w/cyl, so which w/cyl is affecting the locking shoe, the hosed one or the bleeder one?
"

The problem shoe is the lower shoe (the trailing shoe). Take a look at this picture:

mb_brakes_190_front6.jpg


It's the shoe on the lower left.

The bleeder is on the other side of the plate, in the upper left ("north west" on the compass).

T.
Edit: the front of the car is on the right.
 
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