Hi again. On a drum brake with self adjusters. If there was a scenario where the spoon was not in contact with the star wheel because of a misapplied or misaligned spring (preventing contact), could that circumstance cause the brake to self-overtighten?
The arm is there to ratchet the star wheel to tighten as you use the brake (self adjusting). The spring across the star wheel is to keep your manual adjustment from backing off. I would think even if you had the star wheels on the wrong side they still wouldn't over tighten that much (if any). But if they become so loose (stayed short from lack of adjustment) that they might drop down out of the recessed area and then the shoes would not return to the regular at rest location.
If everything is correct I’ve heard of fronts over tightening because it happens when you back up and press hard on the brakes but never the rears.
In theory, the auto adjusters move the star wheel only if there is enough brake shoe movement when braking in reverse. If the shoes are already in good adjustment there will not be enough shoe movement to allow the adjuster lever to turn the star wheel.
I can't claim any first hand experience. But I do remember an auto tech instructor describing this phenomenon years ago. Years ago, as in back when four wheel drum brakes were still commonplace. If brake drums got hot enough the inside diameter would increase slightly until they cooled down. While things were still hot and the drum was slightly expanded, if you were to back-up at a high enough speed and apply the brakes quickly, the self-adjusters would sense the additional clearance between the shoes and the drum. This would allow the adjuster levers to actuate the star wheel on the adjuster a notch or two to compensate for the additional clearance. In other words, the self-adjusters would work as they were designed to. The problem however occurred as the brake drums cooled to their normal temperature and returned to their normal, slightly smaller diameter. The result was that the brake shoes were now over-adjusted and would drag on the drum or even lock-up the wheel. The cure was to manually take out a click or two of the over-adjustment thru the adjuster slot in the backing plates. The other "cure" was to avoid braking while backing up while the brakes were over-heated. The problem seemed to happen mostly on vehicles that saw heavy brake use for prolonged periods. Police pursuit vehicles and highway patrol cars and the like. Or loaded trucks slowing down on an exit ramp to pull into a truck stop or gas station. But as jimmysix noted, it wasn't a problem unless the driver backed the vehicle up and applied the brakes while everything was still hot. And since they supplied most of the stopping force it makes sense that the front brakes were more susceptible to the problem.
I was always taught and then taught that the self adusters were designed to work when you hit the brakes while hitting the brakes when backing up. Some rears seem to adjust when you use the park brake. When I was doing brakes every day I adjusted an untold number of self adjusting brakes that were working right simply because the owners never seemed to back up enough and hit the brakes enough to get them to adust or on the rears they never used the park brake. I've got home made tools in my tool box to either push or pull the aduster lever out of the way so the star wheel can be backed off when they are too tight or when you want to back them off to get the drum off. I've also got a half dozen brake spoons because one style won't work with all of the adjusters.
An experience I had was hot brakes tightening up due to what turned out to be a faulty master cylinder. We rears would tighten up, we would stop and bleed the rears, then we could proceed, but a couple days later, while on the same trip, we would have to bleed again.
Deathrowdave, I've been thinking about this and let me know if my theory holds any water. Given the one-way nature of the star adjuster and the spoon, on a correct setup, the ratcheting action will only allow the star wheel to turn in a way that tightens up the brakes. So if only the star wheels were switched between left and right, my thinking is that due to that one way ratcheting action, if any ratcheting were to occur that it would only cause the brakes to continue to loosen. What do you think?
I will have to sit down and put on the thinking cap . I was just brain storming. I’ll get deep into thinking about it and discuss in a bit .
I changed single '55 Chev master that I had rebuilt at least once, for a Mustang dual and that problem was solved. Yes, a different master solved the problem. In my case it was not a flex hose deteriorating.
I think (there's trouble) that most with auto adjusters are off set to one side, so to swap adjusters left to right you would also need to swap the arm. I've personally never seen an adjuster over tighten by itself........I've seen many people over adjust the brake manually. I would say you have a different problem if they're getting tight by themselves.
I've been reading that question for two days and still have a hard time understanding exactly what the deal is. Exactly what brakes as in year and model of the axle donor are you working on so I and maybe others can look at an image and figure out what you may have done wrong. You didn't by chance decide to install self adusters on an older Ford 9 inch that didn't have self adusting brakes and forget to take the spring that the star wheel normally clicks against off? On most self aduster setups it is hard to install things wrong without something coming loose or breaking. Some adusters pull up an some push down. Let us know what you are working on and if you added self adjusters what year and model of rear you started with and what year and model of adusters you used and we will go from there. If the aduster (star wheel) is put on the wrong side, it will back the brakes off rather than tighten them up.
If the spoon, or adjusting lever, is not in contact with the star wheel (ever), the brakes will not adjust to a tighter position. The spring tension across the lower ends of the brake shoes will tend to keep any movement of the star wheel going in the direction of loosening the brake adjustment. It's doubtful that there would be any great amount of movement of the star wheel anyway, so it would take some time for any noticeable change in adjustment.
You know that over-tightening of self adjusters started being talked about when they first came out. People actually had them taken off their cars because of this. However, in the 60 + years since they have been on cars, I've never seen one over adjust. Heard a lot about it like, "I know a guy" stories, but I've never seen it. I saw a similar problem on heavy truck when automatic slack adjusters came out. Again, I never saw one over adjust.
On a similar thread, there was a lot of discussion as to whether there was enough free brake pedal travel to allow for some fluid expansion as it heats up. How would OP describe the free tavel of pedal, before braking begins to occur?
Hotrodjohn71 Self adjuster levers are often labeled left and right, and I have never seen where they will fit from one side to the other. Google pics of your brake setup to see if anything is out of place. I would be interested in if your brake shoes have been replaced and if the lining is softer like being able to stick your finger nail into it. My reasoning below but I wonder if the newer linings are to soft and allow the adjuster to tighten when they shouldn't. This is what I have be fighting ot 72 mustang that has factory 4 wheel drum brakes doing the same over adjusting mainly the front but backs a bit slower. Overheating to the point of locking up. History on this car is known, my brother bought it in 73 in almost new condition and drove it without any problem until his father inlaw replaced the brakes and master cylinder in the late 70s, he drove it after this only briefly and parked due to the brakes overheating. Low miles stored inside and started a few times a year. Last year he asked me to go over it and get it road worthy again. I know the master was replaced along with the shoes and slaves and lines when his father inlaw did them back when. I replaced all the slaves, rubber lines and master, blew out all metal lines, no rust on this car at all. Replaced all drums, brake shoes , hardware kits, new adjuster cables and levers, I also replaced all the springs with new twice as the first kits seemed to be questionable, Napas best spring kit and shoes. Master cylinder rod has play, I have not shimed out the master yet but am going to try it. Non power brakes. I have pulled and checked the wheel bearings they looked good. I wondered about runout on the drums but checked ok. I am leaning to the brake shoe lining maybe being to soft and grabbing more than the old linings that seemed to be much harder material. Only other item is the diveter block with the brake lite switch...never had brakes kick me like this before.
Just something to be aware of when converting Manual Drum Brakes, use a coarse tooth star wheel, and self adjusting brakes use a fine tooth star wheel.
I've had self adjusting over adjust. Ask an old head mechanic and hot rodder what would cause this. He ask me when I had replaced all the brake springs. When I told him never he said there's your problem. I replaced all the springs and that fixed it.
I got so tired of my fronts overtightening on the Econoline axle in my Falcon gasser that I gutted the self adjusters, and switched to adjustable stars. Set them up, and never had another issue. Sometimes old school is better.
You wouldn't want self-adj drums on a race car if using drums specifically as a weight saver .. Weight and low drag is what you are after.
I replaced my old brakes on my champ car 9 inch rear end. It had 1.75" non-self-adjusting shoes. The new replacement pieces are 2.5" wide shoes with self-adjusters. The only problem self adjusters ever gave me was when they would not self adjust, due either to the screw threads being rusty and seized or to the adjustment pawl failing to grab the star wheel sufficiently. I use anti seize (sparingly) on the threads and grind the "tooth" of the adjuster pawl at a sharp acute angle to be sure it grabs the wheel.
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