SC M37

[Elwood]

Ideally, the drum contact face would be round and square (no taper from inside to out), and the shoes would be ground true to the measured ID of the drum, using something like an AAMCO 8000.

As a practical matter, drums get swapped, and shoes are run as-is. You might experience accelerated brake or drum wear, or brake pulsing if the components aren't trued up to each other. In worse cases, you might have reduced brake effectiveness if the amount of contact between the linings and drum is not sufficient.

Unless you're buying new drums from Midwest Military, you probably won't find a used drum with lots of thickness and/or true in both directions (round and taper). Turning a used drum can then exceed the maximum ID, although there are oversized shoes available to compensate up to a point.

Since these drums are not center piloted, but are instead centered by the studs and nuts, they'll need to be installed on the hubs to be turned true to the rotation axis centerline. Par. 168 of TM 9-8031-2 explains the procedure.

[Elwood]

I have always been told that you must replace the bearings and races as a set, as they wear together- using a worn part with a new part will accelerate wear on the new part.

Although cones and cups are available separately, I agree, replacing only one part of a tapered roller bearing assembly seems like asking for trouble.

"It is important to note that tapered roller bearings are predominantly sold as individual components. Therefore it is important to know the part number of both the cup and the cone, as they will most often differ and there are often many cup/ cone combinations available. While feasible to replace only the cup or the cone when replacing a tapered roller bearing, it is not recommended as it greatly decreases bearing life." bearingservice.com

[sturmtyger380]

If the bearings from the old hubs look okay. I was going to keep the race with its matching bearing.

[sturmtyger380]

Well bummer on the drums pulled off of the junk trucks. I can feel a considerable ridge inside the drums near the outer edge of all of them. Just too old and worn.

[sturmtyger380]

Well all the hubs from the old trucks had bearing problems. Not major issues but some scored and some discolored. Since I am redoing the truck not going to chance those.

I decided to pull the differential carrier out just to inspect the gears and bearings. On first look it's not too bad. We will see.







Anyone else have ny-lock nuts on your carrier studs? The manual shows split lock washers and regular nuts.

[sturmtyger380]

Well I have been busy away from the truck. Lots of chores get in the way of working on the M37. It took about a week of part time work but I was able to create a tool to use on the differential. I found a tool at the auto parts store that was close to the diameter and added some lugs to fit into the pinion and the differential bearing retainers.

The store tool and the bolt I used to create the lugs:



After welding the bolts on and cutting the extra off I used the grinder to shape the lugs:



Here it is on the differential:



It looks like my pinion is no good anymore, what say you guys?

[just me]

I've run worse, (for a little bit) but that is junk.

[Elwood]

Anyone else have ny-lock nuts on your carrier studs? The manual shows split lock washers and regular nuts.

I've never seen ny-lock nuts on the third member studs, and wouldn't use them myself. Split lock washers, plus some removeable strength loctite (blue), because split-locks aren't infallible, and because the loctite will keep the threads from getting corroded and hard to remove.

Nice work on the improvised tool.

Yeah, that pinion looks like the differential has been submerged in water. What's the rest of the ring gear look like? If the pinion was in water, no doubt the ring gear was as well. Time for all new bearings in that differential assembly, too, probably. Ouch.

[sturmtyger380]

Yep, the bearings and races on both sides of the differential have rust in the lower parts where they were in the water. The gear oil that came out looked old but didn't have a large amount of water in it so I am guessing it was from some time ago before the previous owner got the truck.

So I am off to scrounge the junk trucks I have. If I am right the differentials are the same for the front and the rear of the truck? So I will have four to choose from. Wish me luck.

[Elwood]

Yep, the bearings and races on both sides of the differential have rust in the lower parts where they were in the water. The gear oil that came out looked old but didn't have a large amount of water in it so I am guessing it was from some time ago before the previous owner got the truck.

Doesn't take much water, just time. Since the axles on these trucks are vented to the atmosphere (i.e. not closed vented like the brake master cylinder, etc.), it's not difficult for moisture to enter, and it's why the original military manuals require a lubrication drain and change after fording.

If you're running unlockable hubs on your front axle, remember to engage them and the 4wd mode in the transfer case every so often (on loose surface road, of course) and drive a bit to keep lube oil on all of the machined surfaces inside the differential and transfer.

So I am off to scrounge the junk trucks I have. If I am right the differentials are the same for the front and the rear of the truck? So I will have four to choose from. Wish me luck.

Correct. The third member assemblies are interchangeable front axle to rear axle.

[sturmtyger380]

Well I waited until late evening due to the heat index being around 100 degrees! Ran the air hose out to the first truck to use the impact wrench.

Well this truck had Nylock nuts on it as well. Ten minutes later I had the diff out - no deal - rust pits on the pinion - less rust but still not shiny. I will try the next truck rear end tonight. I might have to pull the front axles to get to the front diff.

[rickf]

I'll bet these were used for wheeling in mud, watery mud gets everywhere and once in the diff it grinds away very quickly on gears and bearings. I had a 4x4 shop here in NJ in the late 70s when there was still legal four wheeling and most of what we have is mud and water. I replaced a LOT of rears! And wheel bearings.

[sturmtyger380]

Well the other trucks rear had no lube in it so it was totally toast. But once again I ran into nylock nuts. The history of the two junk trucks is that they were bought surplus from the local Air Base many years ago. Then were put out to pasture and not run until a friend of mine helped me drag them home. The truck I am working on after the Military was in use by the Alabama Forestry Commission after being rebuilt by the Anniston Depot. What's the chance that all three trucks have nylock nuts!

[Elwood]

Maybe the Anniston Depot had an excess supply of those Ny-lock nuts, and used them on everything? Nah, the Army would never do such a thing.

So out of three trucks on hand, you don't have any usable third member assemblies?

Don't scrap those other ones however. Ring and pinion and bearing sets can be replaced.

[rickf]

Maybe the Anniston Depot had an excess supply of those Ny-lock nuts, and used them on everything? Nah, the Army would never do such a thing.

So out of three trucks on hand, you don't have any usable third member assemblies?

Don't scrap those other ones however. Ring and pinion and bearing sets can be replaced.

But check the spider gears also and the spider pins. If the gears look that bad I am betting all of the moving parts are going to be bad, Spiders, the spider cross, all bearings and the ring and pinion. So basically you are left with the housing and the bare center section. Not much to work with.