Please help with parking cable
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Senior User
Joined: Jun 2012
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Thanks for the encouragement. It's amazing how many times something intimidates me because I've never done it before. Afterwards, I wonder why I was so intimidated. Drum brakes always looked so confusing to me, especially compared to disk brakes.
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
Don't be afraid to make a mistake. If you do, back up, fix it and learn from it but don't dwell on it.
These trucks are dirt simple and, compared to today's vehicles, relatively cheap to fix, no matter what's wrong.
Sometimes they can drive you nuts, but the main point is to have fun with them.
Just my 2¢
More Turbo
Joined: Nov 2003
Posts: 747
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Doesn't the parking brake also adjust the rear brakes?You should be able to pump the parking brake pedal while holding the lever out.My understanding is that it will pull the tab up and catch the teeth to turn it
. Seems like I done this before and the brake pedal got firmer.
. Seems like I done this before and the brake pedal got firmer.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Doesn't the parking brake also adjust the rear brakes?You should be able to pump the parking brake pedal while holding the lever out.My understanding is that it will pull the tab up and catch the teeth to turn it. Seems like I done this before and the brake pedal got firmer.
. Seems like I done this before and the brake pedal got firmer.On these trucks, the automatic adjusters work when the truck stops in reverse.
When you hit the brakes, the shoes rotate a very small amount, this is the self-energizing action. The amount of rotation depends on how much clearance there is between the shoe and the drum. The greater the clearance the more movement there is in the shoe. The little cable anchors the adjuster arm and holds it in position, the shoe movement makes the adjuster move in relation to the arm. When there's enough movement, the arm moves the star wheel one notch, taking up the clearance.
The reason why it works only in reverse is to keep the brakes from adjusting too much. If the brakes get overheated from extreme use, the drums can expand quite a bit. If the adjusters work with forward motion, they would take up this clearance and when the brakes cooled down, the adjustment would be too tight and either cause overheating and rapid wear or just plain lock up.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
I mentioned "self energizing" brakes, by design most drum brakes have a primary and secondary shoe, the reason for the different lining lengths. By design the secondary shoe contacts the rotating drum and the slight rotational movement helps to "force" the primary shoe against the drum. This in effect gives the brakes a sort of "mini-power brake" action, taking less pedal effort for a given pressure.
Disc brakes don't have a self energizing action so they require higher line pressure to be effective.
A secondary reason is drum brakes have a larger lining area compared to discs, but the main reason is the self energizing action.
Disc brakes could be designed to be self energizing, Chrysler actually had a self energizing disc brake set up in the forties. It was a very complex set up and was never satisfactory so was dropped.
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