73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: Cheyenne1010 on June 10, 2018, 08:43:20 PM
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I got a 1973 chevy C10 and I'm doing the rear brake shoes
I notice the shoes are not exactly alike,one shoe has more brake material then the other one,why is that?
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Are you saying it’s thicker or longer? The longer one goes toward the front I believe.
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The 73-87(91) GM trucks use a duo-servo brake system. The primary (forward or leading) shoe on both sides typically has shorter friction lining than the secondary (rearward or trailing) shoe. Duo-servo brakes are self-energizing, meaning that as the shoes are forced outward against the drum by pressure applied via the wheel cylinders, the forward movement of the vehicle and rotation direction of the drum rotates the primary shoe toward the secondary shoe through the automatic star adjuster located at the bottom of the backing plate. Since the automatic star adjuster is not anchored to the backing plate the rotational force of the primary shoe forces the secondary shoe into the heavy anchor pin that is fixed in position at the top of the backing plate, amplifying the outward force of the secondary shoe against the drum. Because of the self-energizing effect of duo-servo brakes, the secondary shoe presses outward against the drum with greater force than the primary shoe. Hence, the secondary shoe has more friction material (the lining has greater surface area) than the primary shoe to help equalize the wear on the shoes.
When backing up, the same principle applies except the drum rotates in the opposite direction. When backing up, the primary shoe presses against the drum with greater force than the secondary shoe (the roles are reversed). However, since so little time is expended braking while backing up, accelerated wear of the primary shoe is not an important consideration.
So, the important point to remember is that the secondary shoe has longer friction lining than the primary shoe and mounts in the trailing or rearward position.
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Thanks for taking time to explain all of that.
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Extremely well described, BD. Thank you.
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bd is the Man!
Pretty cleaver how they designed the star adjuster to self adjust the shoe clearance while backing up.
I have to remind myself to deliberately come to a full stop in reverse so they adjust.
Unless you say we don't need to...?
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Coming to a full stop is unnecessary. It merely requires a moderate to aggressive depression of the brake pedal while backing, preferably in a straight line to keep the adjustments balanced side-to-side.
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I thank you and my NECK thanks you ;D
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Which neck?
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The one my head rests on... 8)
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Just checkin'. 8)