How do you get full brake shoe contact with drum brakes?

[Fordiesel69]

So whenever I have rebuilt rear brakes and either turned the drums, or got new cheap drums, the brake shoe will only wear 2/3rds in the middle. The two ends of the friction material does not wear for many thousands of miles. This means extra braking power is being lost. Is there some trick, or any way to bend the shoes?

I am also considering the purchase of a brake lathe, and I was wondering if drums can still be turned? If this is done, wont the diameter increase, and therfore make even less pad contact?

 

[mk378]

There was another machine to shave the middle part of new shoes, making their curve radius larger to match the drum. But no one does that any more. The process is called "arching" the shoes.

 

[eljefino]

The shoes are supposed to cam on their mounts when rotating forwards, so they self-actuate, like primitive power brakes. I imagine during this movement they should also "flare out" and grab the drum properly.

Give everything a jiggle, stuff should be able to move 1/8" or so without binding.

Other than that, get new shoes and drums at the same time, and the hardware/ spring kit too just to be sure.

Are you chasing a performance problem? Do your shoes break in properly and then wear well once they've taken the shape of the drum?

 

[Tman220]

Despite common belief, you will not increase stopping power by getting more of the shoe surface to contact the drum. I would simply wait for them to wear in rather than goofing around with it for no good reason.


To keep things as simple as possible, 5 lbs of pressure from your right foot will create the same braking force whether it is acting on 10 square inches of pad material or 1000

The real difference is wear and heat dissipation, more pad/shoe contact spreads the load and heat over a larger surface area.

 

[benjamming]

yes drums can be turned

 

[nthach]

Unless the drums were machined on dedicated equipment, and you have used OEM shoes there’s no way to ensure the shoes will have full contact with the drums. That’s why aftermarket drums are hit or miss.

The best you can do is to ensure the drums you’re installing are true, not bellmouthed and the shoes are properly installed. this means lube them when they’re in contact with the backing plates. Shoes are meant to slightly rotate in the direction of wheel rotation.

 

[Fordiesel69]

Im not doing brakes at the moment. I was revisiting this topic as im most likely going to buy a brake lathe and want to do both rotors and drums. However if drums are not worth it, I may not worry about getting the odd bits for the lathe.

I only have a few family members left that have drum brakes but remeber this is an issue I always had struggled with. And yes I always rebuilt 100% with new hardware but would drop off the drums for machining, and i always used aftermarket brake shoes as OEM were never avail and if they were they would have been expensive.

 

[paulo57509]

In the old days, the machine shop would cut the drums and then grind the ends of the frictions so that the frictions would have a high spot that would wear into the radius of the drum. Now, there's no need because the ends of the frictions are pre-ground.

"Dust mask? We don't need no stinkin' masks!"

 

[lbhsbz]

This is what you want....contact in the center 2/3s of the shoe. If the top edge of the leading shoe makes contact first, it'll pull the shoe into the drum and lock up the brake. Shoes should not be arc'd round, but on a bit of a "cam" profile....or if round, to a bit smaller radius than the drum, when new. You're not giving up friction. You could actually cut the top half of the friction off of the leading brake shoe and get far higher friction levels...but then it would be undriveable.

Drum brake systems are more about geometry than surface contact area