PRI (small, front) Drum Shoe Wearing More than SEC (large,rear) Shoe

[6volt]

Low mileage C20 truck front brakes done in 1995 with new wheel cylinders, springs, etc.

Front shoes are 5/64 and the back are 10/64.

Everything seems to be working perfectly. Shoes wearing evenly across face and also same on each side (L and R).

I am tempted to reverse the shoes to even out the wear.

Anyone try this?

[cdowns]

a dumb idea // as cheap as brake shoes are to replace if you cant afford to replace them every 12years or so maybe you should get rid of the truck

[6volt]

My main concern is that there is something wrong and I would like to understand it and fix it.

As far as replacing them, they still pass inspection by a good margin so there is no reason to replace them.

I only posted this because I thought maybe other people had seen this behavior and had figured it out.

[67ChevyRedneck]

There is nothing wrong. Front brakes tend to wear faster than back brakes. More weight and stopping power up front.

[mshirey]

You got me thinking about this and was wondering if it might be related to the surface area of the shoes. Assuming the force exerted on the front shoe and rear shoe is equal the psi on the smaller shoe would be greater due to the smaller surface area. This might accelerate the wear on the smaller shoe. Just guessing though.

[67ChevyRedneck]

I'm confused, are we talking about front shoes and rear shoes as in front vs rear brakes or are we talking about front shoe vs rear shoe in THE SAME drum???

[GMCBubba]

sounds like he's talking about front shoe and rear shoe within the same drum (based on his primary and secondary reference). if talking about front drum vs rear drum, the front wheels always see more braking action thand the rears

[70rs/ss]

The shoes are different thicknesses as well within the same drum. The rear of the front drums see more friction the the front shoe does, so it is thicker to begin with. It sounds to me like there is no issue, you just didn't know that the shoes are manufactured differently. If you started with 4 shoes (enough to do the fronts) that were all the same thickness the two shoes facing the rear of the truck would wear out way before the forward facing shoes, because as the brakes are applied the inertia is absorbed in the rear shoe more than the forward shoe. Hope that makes sense? They were different thicknesses new, so it makes sense that they'd be different thicknesses now.

[6volt]

While I can't say whether the 2 shoes were different starting thicknesses, I did record a single number for new thickness when installed. I believe it was 11/64's.

One way to visualize how the shoes work is think about how the shoes are kept from rotating with the rotating drum when the brake is applied.

In short, the brake assembly is kept from rotating by the rear shoe reacting against the big pin on the top of the backing plate.

But any friction force generated by the front shoe appears as additional actuation load on the rear shoe.

If each shoe was reacted on its own pin with its own wheel cylinder, there would be no PRI and SEC shoe. (There are brake systems like this!)
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I looked at my rear brakes today and they are installed properly (small in front) and they are wearing evenly with just a little more wear on the fronts.

I am suspicious of the effect of wheel cylinder condition on all of this. Ironically, on the rear brakes, both wheel cylinders were rebuilt in 1995 and while no brake fluid was dripping from them, when I pulled the boots back, a few CC's of fluid poured out.

So rear brakes with rebuilt wheel cylinders that were starting to leak, did a better job that new everything in the front done at the same time.

I really can't explain any of this.
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I remember back in the 70's some brake shoes came in a pink and grey lining and small and large. It was obvious they were using different material for the PRI and SEC.