I replaced the shoes of the rear drums of the Caravan yesterday. I spent a few minutes looking at the adjuster mechanism and I can't figure out how it works. I set the shoes without springs to simulate the service and park brake motions but the adjuster just sat there. Presumably over the life of the pads the star wheel turns to take up the slack. But what turns it? There is a lever that rests on the star wheel that serves at least the purpose of not letting the star wheel relax the adjuster. Does this lever spin the star wheel the other way? Is it only for the park brake or is it for the service brakes as well (same shoes in this case)?

Thanks,
Sixto
95 S420
87 300SDL

When you engage Reverse and then apply the brakes the counter rotation advances the star wheel{thanks to the built in free play} which is attached to a threaded rod that spreads the shoes incrementally,been in use since the late '20's.................get an old copy of Chilton's or Motor's manual.

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Back-up real fast and slam the brakes on!

Literally!

When I do brakes, I always add a little never seize to that threaded pin between shoes because I have seen them rust and not turn.

Well you don't need to do it fast, or slam the brakes

Have enough movement that you can apply the brakes slowly to a full stop for 30 to 50 feet. Possibly do it several times.

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KLK, MCSE

1990 500SL

I was always taught to respect my elders.
I don't have to respect too many people anymore.

Just to clarify, the question is how does the mechanism work, not how do I get it to work.

Carleton is on the track but I don't see how the wheels spinning one way or the other cause the starwheel to turn.

Thanks,
Sixto
95 S420
87 300SDL

Both ways the starwheel will turn. Going backwards the momentum causes the brake shoes to push outward a slight millisecond so the thing will click.

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You don't need a weatherman to know which way the wind blows - Robert A. Zimmerman

Kuan, lets take it down many notches. What turns the starwheel? There's a lever that goes from one of the shoes to the starwheel. It's the lever you push aside to manually turn the starwheel so you can pull off the drum. Does that lever turn the starwheel in the other direction?

I think I see the point about going in reverse. The trailing shoe will be somewhat forced out when braking in reverse which will unload the adjuster. Then whatever acts on the starwheel does so to pick up the slack. I take it the adjuster doesn't expand so much that the brakes drag.

Thanks,
Sixto
95 S420
87 300SDL

Notice the upper spring rides across the star wheel. On 60's Chrysler products, there was along with that spring a tab that when in a reverse direction of the drum, (brakes applied)the shoes movement in that direction raised the tab upward and when the brakes were applied again going forward, the tab would come down inserted into one of the points in the star forcing the star to advance one spoke of the star. The opposite side of the car star threads if I remember had left hand thread.

I think the tab would only land on the next spoke in the star when enough brake material wore off, so they could not over tighten.

Our MB's use this method in the emergancy brake shoes too!

Essentially there is a certain amount of interference,or free play engineered into drum braking systems,If you've ever done a brake job on vehicles so equipped you will know what I mean when trying to re-assemble the shoes and line them up to accept the springs.

The following may explain it more coherently than I.http://www.babcox.com/editorial/bf/bf10216.htm

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Folks,

Hopefully I can explain... I'm not up to date on Chryslers, but have done enough others. The top pin is fixed, the wheel cylinder presses out the pads, and they contact the drum. The bottom of the brake pads rotate a bit forward or back depending on the rotation of the wheel. Most adjusters are designed to active on reverse braking.

When the pads expand they contact the drum, and rotate at the bottom... there is usually a cable attached to the top pin that goes around a holder about midway on the brake drum and then goes down to the adjuster arm. The arm is also usually attached with a spring to the other pad.

The cable keeps the adjuster arm in place, but the bottom of the pad assembly moves with the rotation. You can do this with the drums off to see some of the motion. If the brake pad has worn, the pads rotate more, and the adjuster arm will catch the next bump on the adjuster star wheel. The star wheel is attached to a threaded shaft that lengthens as it is turned. When the brakes are released, the springs attached to the pads pull them back to the central location. If the adjuster arm caught the next notch, it will turn it in the direction to expand it as it returns to rest position. This makes the bottom of the brake pads wider, so next time they don't rotate as much and maybe no adjustment is made. The adjuster arm also prevents the star wheel from turning so they don't loosen.

So what usually goes wrong??? In the initial setup you can have the brakes either too tight or too loose. Too tight and it will be hard to get the drum on. Once you have it on it will be very hard to turn. If they are too loose, they may not catch enough to adjust.

Once you install the brakes, put on the drum and wheel. Turn the wheel and if there is no drag it should be tightened a bit. In my experience you want just a slight bit - usually attributed to high spots that wear away quickly. If too tight you want to loosen the adjuster. They make tools for adjusting or use a screwdriver. There is usually an access window on the bottom of the backing plate. Put the tool in there and rotate the star wheel in the direction to tighten or loosen as needed. You should be able to hear the click - click of the adjuster arm on the other side of the wheel.

Drive the car a bit, do a couple of backup stops to have the adjuster system work by itself.

Hope I didn't confuse the issue more...

Chuck

There were some systems that worked from the parking brake instead of from reversing. I may be thinking of 60's cars.

Whenever I disassemble drum brakes I always replace the adjuster screw with the starwheel. It is cheap (but don't buy the made in sweatshop junk) and they love to stick, don't lubricate the threads it attracts dirt and moisture and gums up the mechanism.

Be sure you understand the leading shoe arrangement, most people don't.

Get a little bottle of brake caliper grease with a brush in it and learn to use it.

If you don't know how to work on your brakes or steering, get help. A mistake in these areas may cost you everything.

Now you've got me wondering. Do I have any right to work on a system I don't fully understand? I do everything by the book and it looks and works as it should. Doggone it, enough things keep me up at night

Sixto
95 S420
87 300SDL