The Stovebolt Site Forums The Shop Area Driveline Turning a rear brake drum

I installed disc brakes on the front of my 42 1/2 ton but kept the stock rear drums. put new wheel cylinders, shoes, springs, and emergency cables. The drums need to be turned but I cannot find the specs to see if I have enough material left. I don't want to spend $200 on new drums if I only need to spend $30 to turn them. Any leads to where I can find the specs? looked in my shop manual but could not find them.

Check your drums to see if you can tell if they have been turned before A brake shop may be able to look up the specs also .

As a general rule of thumb, passenger car brake drums can be turned .060" oversize safely, and most 1/2 ton truck drums will handle .090" over without a problem. If you're dealing with 3/4 ton or larger stovebolt drums, don't machine them at all, as they're virtually impossible to replace. New ones don't exist and "good used" drums command a king's ransom if they're available at all.
Jerry

Jerry, I don’t feel embarrassed to admit I’m only a “weekend mechanic” and don’t know a thimble full compared to you and others. My question is are there differences in the front and rear drums on our 1/2 ton trucks or are they interchangeable? How can you tell them apart at a swap meet for example?

I'm pretty sure the 1/2 ton drums will interchange front to rear, BUT- - - - -the fronts were riveted to the hubs and unless somebody has cut the rivets away, you'll probably find front drums with the hubs still attached. A little work with a drill press to take the heads off the rivets will free up the drums so they can be slipped over the rear axle flange studs. In some cases the drums were a slip fit, not riveted, and they were held on with sheet metal spring steel retainers to keep them from coming off during a tire change. I've seen some front hubs that had the lug studs swaged into place, and they also held the drums onto the hub by the swaging procedure. A special cutter was required to spot face the swage away before removing the drum, in that situation.
Jerry.

Jerry is correct (as usual)
1/2 ton drums are the same front and rear. They're not riveted, however, but are held on with the lugs swaged into countersinks in the holes. The shop manual says that the lugs can be pressed out without removing the swaged metal from around the lugs. It does say to re-swage the lugs, but I think you could get away without doing that. The lugs built for swaging might be hard to find, and you need the tool as well.

[on edit}Whoops! The above only applies to '51 and above.

'40-'50 brake drums are different front and rear on 1/2 tons.
Fronts are PN 602432 and Rears are PN 601985

to the OP, some brake drums have the maximum service diameter cast into the drum. I've seen it before on the outer rim. You might check to see if your are marked.

Hey Hotrod Lincoln,

I hope this isn't out of bounds for this thread. I am looking at my 1.5 ton drums and was thinking about turning them to clean them up. However they do not seem to bad and I was considering hand sanding or some other abrasive to clean them up. Is there some veteran method to do it?

I'd suggest using a sheet of 80 grit sandpaper like body workers use for roughing out Bondo, folded into a square that's about 1/4 the size of the original sheet. Give the drum a vigorous scrubdown, followed by a cleanup with spray brake cleaner and a rag. Another sneaky trick to make the new brake linings wear in to the exact shape of the drum is to glue a piece of the same grit sandpaper to the inside of the drum and scuff the newly relined brake shoes against if to match the brake to the radius of the drum. Otherwise, you'll need to adjust the brakes repeatedly as the lining "wears in" to full contact with the drum. If you use a water-soluble glue like original Elmer's white glue, a quick splash of boiling water will remove the sandpaper easily.
Jerry

Mount the drum on the lugs finger tight with the inside facing you...then you can use one hand to rotate the drum while the other does the deglazing and smoothing.

Hey Guys, Thanks for the info. I think I saw the gluing the sandpaper trick somewhere in another thread. I am assuming you glue the sandpaper on, put the drum on, rotate by hand, pull off, inspect, "rinse and repeat" till the scuff is on the whole pad?

Nope, just use the sandpaper-lined drum on the workbench, and scuff the shoe/lining assembly into shape by hand. It only takes a few minutes, as the lining will be pretty close to the right contour already. That procedures just shortens the "wear-in" process to achieve a perfect fit between the lining and the drum.
Jerry

I have done many brake jobs, new shoes, sometimes new cylinders. I've never turned a single drum or had shoes arced. The drums wear "round" and never had one too thin. Shoe lining conforms in a few miles. Even if drums are grooved, lining conforms and stops vehicle. This is over a span of 60 years. Not saying you should not, just pointing out it's not a serious issue. It was done in the past to make easy money.

Some people are satisfied with half-donkey braking. Then there are the professionals. As long as replacement parts are available, it's important to use the full capability of the brakes, the way the factory designed them. Antique Chevy brake drums are an exception, as the lack of replacement parts makes it necessary to reuse worn and potentially dangerous parts to have any brakes at all.
Jerry

For the fleet, everything got turned. Everything! Not so much these days as it's just parts swap.

Glad to see you are not a half-donkey.

klhansen Found that if you dont cut that swedge off of front lug bolts it will make the hole in the hub to big to properly hold a new lug bolt. Then later can lose the bolt inside the drum during a tire change.

That very well could be. It would be a pretty severe operation to compress that swedge thru the hub hole.
Although modern lugs have a pretty oversize knurl that may keep the lug in place, even with an oversize hole.

Most of the better-equipped shops I've been around had swage cutters that we used before trying to replace lug studs or drums where the studs also retained the drums. Low speed in a drill press, and lots of cutting oil was needed to avoid breaking the teeth off. Those tools were not cheap! Redoing the swage on the new studs could be a challenge as well. I've been known to drill and tap a hub flange and countersink a hole in the the drum between lug holes for a flat head screw or two instead or trying to redo the swage.
Jerry

skydog THey made a machine to grind the brake shoe to perfectly fit the turned drum. 2 drawbacks wastes alot of shoe material,makes a lot of asbestos dust (on old ones) With ground shoes you will get full breaking, if not ground will be noisier and less stopping power when new,also will need to be adjusted as they wear-in .