Before getting a Corvette, you should have a chiropracter on retainer.
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Nevada_545 gives a nice explanation above. (Somewhere around comment #226)
When you back up and step on the brakes, the self adjuster will only click the star wheel one notch IF the required pedal movement has been reached. It does not click the star wheel every time you back up, only when the brakes actually need adjustment.
A disc brake system stays pretty consistent because when you apply the brakes and let up, the pads only move back just enough to clear the rotors. There are no springs to push them back, just the friction of the rotors to move them. As the pads wear down, some fluid from the master cylinder stays in the caliper to compensate for the wear. This is why in a disc brake system, the fluid level in the master cylinder is always dropping.
That is not the case in a drum brake, at least not in the older all drum brake systems. Later model rear drum/front disc systems have a different design for the rear drums that I won’t get into here.
Your drums brakes move the top of each brake show out to the drum, the bottom of each shoe is hinged on the self adjuster star wheel. When you release the brakes, the shoes are pulled away from the drum by springs. There is a cross piece under the wheel cylinder which limits how far the shoes are pulled back.
As the shoes wear down, the brake pedal will go a little lower to the floor before engaging. For normal operation, the small difference is hardly noticeable. When you back up and step on the brakes, the cable is pulled and it in turn pulls up the lever next to the star wheel. If the brakes are still in adjustment, it wont pull it up far enough to catch the next notch on the star wheel.
When the brakes have worn down enough, the pedal stroke required to stop in reverse will finally pull the lever up enough to catch the next notch and it will click one notch down, bringing the shoes back into proper adjustment.
When new shoes are installed, it may take several reverse stops to get the shoes properly adjusted. In you case though that would not have worked for you as there were other issues. Self adjusting would not have been able to overcome those.
But after the initial adjustment, the self adjuster will only activate the star wheel occasionally.
Now I am going to urinate on a couple of suggestions above. Do not do hard braking in reverse at elevated speeds to make this adjustment. The harder you press on the rake pedal, the further it will go down. By forcing it to go down more, it will make an adjustment when it is not needed. That will cause your brakes to be too tight. It will give you a little better brake pedal feel, but it will not increase brake efficiency. You will stop just as fast with the correct adjust as you will with tight brakes.
But tight brakes will wear down much faster and reduce your gas mileage due to increased drag. Just brake normally when backing up and if the brake job is done right, all will be well.
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Hi Keith:
Just curious. Is the above really true?
The amount of “self-adjusting” is dependent on how far the adjusting lever is rotated counter-clockwise when braking in reverse.
Isn’t that movement limited by the shoes expanding to the drum (where the leading shoe is anchored to the pin at the top), and not by the speed of the drum’s rotation or the intensity of the braking?
Keep in mind that a drum will flex when braking, you can take a new/old drum and put a drum mic in it and squeeze the drum with your hands and move the dial on the mic, so yes pressure can affect the travel of the shoes due to the flex of the drum… You can’t see it but you can measure it… Yes I have done it many times… That is one of the many reasons why drums have a discard spec on them… The thinner (wall thickness, yes I know drums get bigger as they wear out as measured) the drum the more the flex and less efficient it is on top of the other reasons why oversized drums are bad…
Joe, we are kind of in agreement here. The remark about elevated speed was for safety. Elevated speed is not necessary.
How far the adjusting lever is rotated is dependent on how far the shoes move. Shoe movement is directly related to pedal travel. The more the shoes are worn, the more the pedal travels, but enough pedal travel for normal stops and pushing the pedal as hard as possible results in two different lengths of pedal travel. Pushing as hard as possible can cause the adjusting lever to rotate far enough to catch the next notch on the star wheel where a normal pedal pressure might not catch it until for another 500-1000 miles.
Also @davesmopar is right about the drum distorting.
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Resolved. There was a partial obstruction in one path of a cube-shaped part attached to the rear differential housing. I don’t notice any effect on braking performance however. Good braking before, good braking after.