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Old 08-01-2019, 02:10 PM
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rear drum brake shoe orientation

guys,

I'm installing a new rear on my 70 GTO and swapping the brakes over, standard 9 1/2" drums. The service manual says the primary (bigger) brake shoe goes toward the front, but the current set up on the old brakes has them toward the rear. Can someone confirm for me where the bigger brake shoe is supposed to go?

Mike

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Old 08-01-2019, 02:24 PM
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The shoe with the shorter lining is the primary and goes towards the front. Longer lining towards the back.
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Old 08-01-2019, 03:21 PM
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It only matters if you have and are using a parking break. In that case the cable is routed in the front or rear of the drum. The cable pulls on the parking brake which piviots on a point increasing leverage.
It has been almost 50 years.
Someone could have installed a diffrent axle or backing plate that requires the smaller one on that side.

Other then interference or some aftermarket thing requiring special pads it does not make a diffrence what way they are mounted.


Also. Buy a all in one brake tool. You can do the job with screwdrivers snd wrenches. But that $10 or so tool is worth every penny.
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Old 08-01-2019, 04:05 PM
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Quote:
Originally Posted by cerial View Post
It only matters if you have and are using a parking break. In that case the cable is routed in the front or rear of the drum. The cable pulls on the parking brake which piviots on a point increasing leverage.
It has been almost 50 years.
Someone could have installed a diffrent axle or backing plate that requires the smaller one on that side.

Other then interference or some aftermarket thing requiring special pads it does not make a diffrence what way they are mounted.
Sorry, but I have to disagree. The leading shoe is self energizing in the direction of travel. Since MOST of your high speed driving is forward, the front shoe is the one that's self energizing. The reduced lining area on the front shoe is designed to help balance the loads on the two shoes so they wear somewhat evenly. The metal backing part of the shoe is the same on both, so the parking brake is irrelevant. In fact, on 1980s GM cars, the parking brake cable comes in from the front on one side and the rear on the other side so they could save a few pennies per car by only having one backing plate. The shoe with the smaller lining still goes towards the front. And frankly, it lining size didn't matter, manufacturers wouldn't incur the extra cost of having two different shoes in each lining set.
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Old 08-01-2019, 05:49 PM
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Semi brakes use the same size shoes in all there drums.

Most wheel cylinders are double acting.
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Old 08-01-2019, 07:43 PM
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Quote:
Originally Posted by cerial View Post
Semi brakes use the same size shoes in all there drums.

Most wheel cylinders are double acting.
I have no experience with semi truck brakes. I DO know that GM A-body brake shoes are not anchored to the backing plate at the bottom. The upper edge of the front shoe is pushed outward by the wheel cylinder. Rotation of the drum rotates the two shoes and self adjuster towards the rear pin on the wheel cylinder.

This rotation is how the self adjusters work.

Yes, the wheel cylinder is double-acting, but the pressure inside is the same on both pins, and the added friction force rotating the shoe assembly around pushes back against that rear pin.

I'll ask again: since GM pinches every penny possible, why would they go to the expense of having to stock two different shoes for primary and secondary if a single common shoe would work?

To the OP, since I missed this in your first post originally, I don't know what you're reading, but the shoe with the SMALLER lining is the PRIMARY shoe and goes to the front.





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Old 08-02-2019, 06:13 AM
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I know as a kid long before I could drive, one time doing mopar brakes which had this stupid little rivet like metal piece that gets hammered in one shoe, I put it on the wrong one and left it that way. So the smaller lining had to go to the rear. When the next inspection came my Mom told me that the car needed rear brakes, only because the last set on one side was put on backwards. So it made a big difference in wear.


Remember when brake shoes had a core charge?
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