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Tips
Tips

drum brake symptom

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There is a sping inside the cylinder.
Naught a stiff spring, and there primarily to hold the cup against the piston, and keep the piston/cup from retracting on rough road vibration.

If you can push the piston back with a screwdriver, that is generally sufficient.
Compare it to the other cylinder on the same side that does NOT have a locking shoe syndrome!

How far in?
Depends on shoe wear and drum wear, but probably 1/2" or so on a single-ended cylinder.

What you look for is corrosion, pitting, especially along the line you will see where the cup resided.
If it doesn't hone out, replace it.
Or, send it off and have it sleeved (but do all 4 fronts at the same time).

I still wanna know what happens when you unlock the tab on the pivot bolt for the show with locking syndrome and try to move the bolt head....does the shoe try to shift position in the direction of the wrench movement at all?

Important you watch that shoe first crack with the wrench, 'cause if you break any corrosion loose THEN look, you won't see it, and it may be harder to diagnose once apart.
 
TOC said:
I still wanna know what happens when you unlock the tab on the pivot bolt for the show with locking syndrome and try to move the bolt head....does the shoe try to shift position in the direction of the wrench movement at all?
Click to expand...

Good point.

The whole thing is a box-o-tricks. When all is right they're great. If one of those things gets funky, it gets hard to figger it out. Tension on the slider (center pin) and cylinder bore issues are still my top picks.

...but I'm still concerned over a possible lip worn on the backing plate, too.
 
Just to be sure I'm following all this:

"what happens when you unlock the tab on the pivot bolt ... and try to move the bolt head"

No movement at all.

"If you can push the piston back with a screwdriver, that is generally sufficient."

OK - I can do that; same "feeling" on both cylinders - both go about 1/4". So does this mean I can pretty much rule out a cylinder problem?

The sad remnant of my brain attempts a cogent thought: if the brakes are not being used (no pedal pressure), then why can I push a cylinder piston stud "in"?

Shouldn't the piston already be "in", and only push "out" when I press the pedal? In other words, why can I press the piston stud in, if the brakes are relaxed?

Ridge on backing plate: where would I look for a possible ridge? Would it be really obvious like a slight raised curve, or something that would be really tough to find? Are you talking a ridge that would "catch" the side of the face of the shoe? or catch some other part of the shoe? or ...?

T.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Are you talking a ridge that would "catch" the side of the face of the shoe? [/QUOTE]

Yep.
 
The piston has a light spring inside the cylinder that keeps it out against the shoe pin.
If it didn't, your first (and maybe second) (or last) stroke of the pedal would go to the floor.

If they feel that same, remember that for now.

You tried to move the pivot bolt and nothing happened...."No movement at all"

Does that mean the pivot bolt won't move at all?
 
Maybe it's just me but when I looked at the diagram I saw the return springs were the same. When I look at the picture, they look like 2 different size springs. ? :confuse:
 
Thanks. The piston studs do feel and move the same. Sounds like that isn't really an indicator of the internal cylinder condition.

Turned pivot bolt - shoe didn't move.

Picture is just an example I found. My springs are equal.

Thanks gentlemen!
Tom
 
Next is A) remove and open the cylinders for inspection, abd B) inspect the backing plate for any possibility of grooves in any mount pads.

However:

Been a long time, but I thought those MB pads floated fully, as in no rubbing support pads to contact.

Might be interesting to swap out springs, top and bottom, just to confirm that is isn't a weak spring.

I THINK you can swap out the cylinders, too, which will help confirm, if the problem shifts, it's the cylinder, if it doesn't, it's not.
 
A clue?

Engine cold, unused for three days.

Pry up the problem shoe. Clicks back into place. Pry it up again, doesn't click back into place. Pound shoe with fist, back into place. Pry it up again, clicks into place.

The "sticking shoe" problem is intermittent.

And, as I haven't used the brakes, or even moved the cylinder piston and rod, seems to me the cylinder has nothing to do with the problem. Shoe isn't welded to the piston rod; rod just sits in the shoe "cup". Cylinder/piston unused - shoe may or may not "stick" after the pry test. Anyone agree with me that the cylinder probably isn't part of the problem?

T.
 
With that brake setup, no agreements until it's fixed.
So, have you pulled the shoes off yet?
 
I don't know what to tell you.
Doc and I both tell you to pull the shoes.

Popping the shoe out by hand and having it stick is NO TEST whatsoever.
That rod that fits into a socket on the end of the shoe can unseat, causing that very issue, that will never, as in ever, show up when you apply the brakes and the piston moves the rod out.
Conversely, there is a pocket in the end of the piston for the rod.
If it's burred, the rod (if it sticks to the shoe) will unseat from the piston pocket, and may very well hang up....sometimes.

Tell me...what was the symptom, when driving, that caused you to think the shoes were locking up?

What you are doing isn't going to prove anything, at all, other than possibly the tension of the boot is holding the rod in such a position that it unseats when you pull the shoe back.

THAT could mean a damaged piston pocket, which means new w/cyl, so, no, absolutely no agreement that it is NOT the w/cyl.

Pull the shoes, then the rods and boots, LOOK at the piston, inspect the backing plate, inspect the shoes, inspect, clean and lube the pivot, THEN we can have some data to figure it out.
 
Okay.
Did you understand the rest of it?

I still would like to know, before Thursday, what was the symptom, whilst driving, that caused you to think you had locking shoes?

Did the wheel lock and not release?
Skid?
Smell badly?

Dave
 
TOC said:
I don't know what to tell you.
Doc and I both tell you to pull the shoes.
Click to expand...

Will do.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Popping the shoe out by hand and having it stick is NO TEST whatsoever.
That rod that fits into a socket on the end of the shoe can unseat, causing that very issue, that will never, as in ever, show up when you apply the brakes and the piston moves the rod out.
Conversely, there is a pocket in the end of the piston for the rod.
If it's burred, the rod (if it sticks to the shoe) will unseat from the piston pocket, and may very well hang up....sometimes.[/QUOTE]

I hear you. But it just seemed to me that having the "stick" and "not stick" happen on the problem shoe, when I know the piston hasn't moved, would tend to indicate the piston isn't in the problem loop.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]

Tell me...what was the symptom, when driving, that caused you to think the shoes were locking up?[/QUOTE]

After about ten miles, I feel the engine having to pull harder to go up a hill. And releasing the brake pedal, I still feel some "drag" on the car's speed, which isn't there when I first start in the morning. After the ten miles or so, I feel the hub and it's MUCH hotter than the other three wheels (wheel discs are off). Get home, raise the front end, right front wheel is free to turn easily; will actually spin. But left front wheel takes a lot of hand force to rotate; no spin possible. Definitely has drag.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]

What you are doing isn't going to prove anything, at all, other than possibly the tension of the boot is holding the rod in such a position that it unseats when you pull the shoe back.

THAT could mean a damaged piston pocket, which means new w/cyl, so, no, absolutely no agreement that it is NOT the w/cyl.

Pull the shoes, then the rods and boots, LOOK at the piston, inspect the backing plate, inspect the shoes, inspect, clean and lube the pivot, THEN we can have some data to figure it out.[/QUOTE]

OK - will do on Thursday. I just thought that knowing the stuck/unstuck problem occurs, even without using the brakes, would be helpful.

T.
 
NutmegCT said:
TOC said:
I don't know what to tell you.
Doc and I both tell you to pull the shoes.
Click to expand...

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] I hear you. But it just seemed to me that having the "stick" and "not stick" happen on the problem shoe, when I know the piston hasn't moved, would tend to indicate the piston isn't in the problem loop.
Click to expand...

You mentioned you had NAPA work on the brakes and after that the one shoe started having a "stick" and "no stick" problem.

I researched the staff at that NAPA and discovered that the person who worked on your brakes is a retired Private Investigator. The problem with your car is simple.....you got a gumshoe! :crazyeyes:

Ok, ok...I know that was of NO help. But hopeful it made you smile....or at least groan!! :laugh:
 
Now, that was bad....REAL bad......

But, to throw more into this....
Lockheed style, with locked pivots, can be a real problem if not set up right, in that the heel can lock into the drum.
Now, direction of rotation dictates this can't happen, but sticking with shoes that are not arced to the drum, and cylinders that are not positioned correctly, or aftermarket cylinders with pivot holes in the wrong place, or.....wrong cylinders (see above on casting numbers).
Who knows what it is until we find it?

Major brake adjustment on OLD cars...there is a slot in the edge of the drum....to fit a feeler gauge into, loosen the main stud, tighten the adjuster as hard as it will go, rap the drum all the way around and re-tighten adjuster, THEN lock the main stud.....

I don't remember all these years later what the process is on those MBs, but one of the reasons you buy MB parts and spend the money is MB parts work.
 
Silverghost said:
NutmegCT said:
TOC said:
I don't know what to tell you.
Doc and I both tell you to pull the shoes.
Click to expand...

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] I hear you. But it just seemed to me that having the "stick" and "not stick" happen on the problem shoe, when I know the piston hasn't moved, would tend to indicate the piston isn't in the problem loop.
Click to expand...

You mentioned you had NAPA work on the brakes and after that the one shoe started having a "stick" and "no stick" problem.

I researched the staff at that NAPA and discovered that the person who worked on your brakes is a retired Private Investigator. The problem with your car is simple.....you got a gumshoe! :crazyeyes:

Ok, ok...I know that was of NO help. But hopeful it made you smile....or at least groan!! :laugh:
Click to expand...

shriek.jpg



argh!
 
Took a day off yesterday but got back in the ponton groove today.

The problem of the dragging brake shoe is solved.

Symptoms: press brake pedal and release. All shoes on all wheels would extend outward, then return inward *except* the lower shoe on the left front wheel. Remove wheel and drum, pry the upper shoe outward (as if braking), upper shoe clicks back into place. Pry the lower shoe outward, release, but lower shoe just barely moved back, thus staying mostly extended. This was causing the brakes to heat up way too much, and gradually freeze the front left wheel.

Took the shoes off and discovered that the inner edge of the lower shoe (the part just under the lining) had been rubbing on the raised area of the backing plate. See picture attached; you'll see what appears to be a slightly raised "plate" just under the corner of the shoe. The plate had a slight bit of oxidation (corrosion) on the surface.

I filed down that raised area on the plate just a hair, then put a drop of ATF on it. Reassembled, tried the "pry and click" test. Both shoes now moved out and back in normally.

I then girded my loins, drove about a mile, raised the front end, and found the wheel completely free to rotate. Drove another 25 miles, and found the brakes and wheel still completely free.

Thanks everybody for all the suggestions. Onward through the fog!

Tom in CT
 
THAT'S the pads we kept talking about!
Now, there is a question.
Now, did the shoe fall off the pad? Then there is something else amiss.
The pads should stay under the shoe at all times, unless the pads are way too thin (doesn't appear to be so), the drums are horribly oversized (quite possible on a car over 50 years old), or the wheel cylinders are wrong, with the pivots in the wrong place for the heel of the shoe.

Looking at your latest photo, I see an angled wear pattern on the shoe.
Hopefully you did that at some point by grinding the shoe surface.
Otherwise, the shoe is not aligned properly (and that could be a wheel cylinder not seated properly).

Too bad you've got it all together.....I'd like to know if the heel (pivot) end of that shoe is making contact with the drum (it will have wear like you see in the picture).

If that shoe dropped off the edge of the pad, that isn't good.
However, if it was just corrosion, that's one of the things we wanted you to look at.

Glad it's fixed.
 
DrEntropy said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Are you talking a ridge that would "catch" the side of the face of the shoe?
Click to expand...

Yep. [/QUOTE]


self said:
...but I'm still concerned over a possible lip worn on the backing plate, too.
Click to expand...

:devilgrin:
 
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