What acticates self adjuster in drum brake? 2

[knowlittle]

I asked this question at hobby-level automotive forums but I got conflicting answers. Some say braking in reverse motion moves the adjuster. Others say engaging parking brake. And that's for the same car.

So here is my question for automotive engineers. Is there a way to tell just by looking at it if it is parking brake activated or braking-in-reverse activated? Thanks.

 

[franzh]

When the brake shoes move more than a preset amount, the movement actuates the adjuster arm usually one notch at a time. When the brake shoe travel is insufficient to lift the arm, it is assumed to be in adjustment.

Almost all of the self adjustment devices actuate from the rear shoe. The rear shoe is anchored at the top in forward rotation, but when in reverse, the front shoe is anchored, allowing the rear shoe to move a little more.

There are generally two types of self adjustments, the cable type that lifts the arm, and the link type that allows the arm to drop, both actuating the star-wheel adjuster. The two types are NOT interchangable.

The self adjustment mechanism should actuate in normal driving anyway.

Franz

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[IRstuff]

The newer ones probably self-adjust, like disk brakes do. The older ones, ala 1966 Plymouth, required backing and braking to move the adjuster.

TTFN

FAQ731-376

 

[evelrod]

Excellent explanation, Franz...however, I think those methods of adjusting the brake shoe clearance are, basically, for American cars. Several other methods are available on 'foreign' cars, e.g., English Ford products that actuate the adjuster by way of the parking brake. Same deal, just uses the p brake to move the actuator instead of vehicle motion. In the 60's when English Fords were popular here in Socal, I used to get all sort of problems with folks that were used to American cars and just never used the p brake!

Rod

 

[knowlittle]

Thank you for the explanation, Franz.
I needed to hear from the source rather than not-always-truthful-internet.

 

[carnage1]

As I recall the ratcheting self adjuster on many cars is actuated by a screwdriver through a hole in the backing plate.
That's why they call it a "self" adjuster, because you (yourself) are the one crawling under the truck cussing about your worn out brake adjusters

 

[evelrod]

Franz, since you are interested in vintage cars, I'm sure you will appreciate the fact that I don't need a screwdriver...I still have several different "brake spoons" from my time at "Marvin Mann's Auto Service" in 1958/59...Also still have my "tappet wrenches" from that era. I have a bunch of other odd tools that were specific to cars of the 50's, too.

Carnage, when I do rear brakes on my trucks (the only thing around here with self adjusters) I have replaced the actuating cable and guides each time...so far after 30+ years of Dodges, no problems...Now the Chebbys, that's another matter.

Rod

 

[franzh]

Ahh, old tools, old cars! I too have my tappet wrenches, a clip puller for the valve guide (ask anyone else what we are talking about? HAH!) and I just saw at auction, an in-car crankshaft cutter for a "T" model. My brake spoons are custom ground, several wrenches show more than few heat marks from being adapted to unique applications.

Several years ago, I sold an old Sioux valve machine that had a lifter refacer attachment. I also still have a babbit shaver and my old prussian bluing bottle. Somewhere I have my old glass surface for checking flatness, a sneaky pete, and who knows what else.

Thanks for the memories, it hurts to think back 40 years ago!

Franz

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[Rob45]

Interesting to see two completely correct answers and two ludicrously far-fetched replies on the same thread...

Hint: Franz and Rod are right.