MTFCA Forum

My sandblaster guy went a little aggressive and roughed up the outside of my rear drums. I use Rocky Mountain brakes. Can anyone tell me if that’s going to tear up my brake linings?

Hard to say without a picture. Most likely they can be polished a bit and be okay.

If you are really concerned, the drums could be mounted in a lathe and polished somewhat with fine emery paper.

Allan from down under.

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I'd dress them down if they were mine.

Brakes work by turning motion & friction into heat to impede motion. Those may turn motion & friction into dust. I'm of the school that they
need to be smoothed ( not polished ) like trans drums. On the other hand they will darn sure seat in fast.
Craig.

Craig, with due respect, brakes create friction to cause drag, to result in braking. They are not there to make heat. In fact heat is an unwanted byproduct of the friction. All braking systems do their utmost to reduce the effects of heat, because heat causes brake fade. Cast iron dissipates heat better than steel. Finned drums help to cool things. Disc brakes dissipate heat far more efficiently than drums. Ductwork helps to get cooling air onto the brakes.

Allan from down under.

Brakes convert kinetic energy to heat. No heat, no braking. Locking the brake still produces heat... at the tire/road interface instead of at the brake itself. You can prevent heat accumulation in brakes by lubricating them. (But you won't have much braking)

Heat escapes brake assemblies via several routes. Some brakes do a much better job of dissipating heat than others.
A cast iron drum can absorb a lot more heat than a typical pressed steel drum, in the short term.

All this "heat" stuff aside...

If you had access to a lathe, or similar way to spin the drums, all you would need to do is to polish the surface with some fine emery paper. They don't need to be a mirror. You just basically want them to feel smooth as you run your hand over them.

Now... back to how brakes make heat...

According to energy conservation law. Energy can neither be created nor destroyed it can only be transferred from one form to another.
Hydrocarbon ( fossil fuel ) is a form of potential energy. Refining it transforms it to chemical energy. Mixing it with air & igniting it transforms
it to thermal energy ( heat) Capturing this heat with a crankshaft, gears & tires transforms it to mechanical energy that creates motion.
Motion x mass = kinetic energy. Kinetic energy + friction = heat( thermal energy) Unfortunately we lost the vast majority of the energy @ the
brakes & the tail pipe.
And that Jason is why it is recommended that you smooth those drums so you can transform that energy @ the brakes instead of @ the pavement.
Myself included I'm starting to wonder about us.
Craig.

Craig Leach wrote: ↑

Tue Feb 27, 2024 10:46 am

Unfortunately we lost the vast majority of the energy @ the brakes & the tail pipe.

Craig.

... and the radiator.

Myself included I'm starting to wonder about us.

Craig Leach wrote: ↑

Tue Feb 27, 2024 10:46 am

According to energy conservation law. Energy can neither be created nor destroyed it can only be transferred from one form to another.

That’s how I feel after work sucks the life out of me all day!

I appreciate the help! I’m glad to know they aren’t trashed.

Does he really need a lathe? How about jacking up a rear wheel with the brake drum on it, put the car in high gear, and hit it with some emery cloth?

I was going to suggest that too BUT if the R.M.s are mounted, not much room to manipulate the emery cloth !

I don’t think that surface is rough enough to worry about. Probably be smooth in no time.


Andy

noelchico wrote: ↑

Tue Feb 27, 2024 6:51 pm

Does he really need a lathe? How about jacking up a rear wheel with the brake drum on it, put the car in high gear, and hit it with some emery cloth?

No. As I mentioned, "If you had access to a lathe, or similar way to spin the drums..."
Your "similar way" suggestion is an excellent one.

I have a lathe, so that's where my mind goes first. Like a carpenter who first reaches for a hammer

When it was stated that the drums were sandblasted, i presumed they were not still on the wheels. That makes them easy to mount in a lathe.

Allan from down under.

Rough surfaces will tear up lining before the metal surface smooths out. Think about transmission drums.
I've chewed up transmission linings by not filing and sanding smooth after turning on a lathe. I would get the brake drum surfaces as smooth as I could.

A blasted surface isn’t rough enough tear up a brake lining. If anything it would help the lining to conform to the drum faster for better braking.


Andy

I agree with Andy. Depending what type of brake lining your using it takes a lot of miles for the lining to wear to get a good mating surface because the band isn't perfectly mated to the drums.