M939 series rear axle seals

[nf6x]

My M936A1 arrived with a nearly flat rear tire. Thanks to the resulting slope of the axle, it was also leaking gear oil where the axle flange bolts to the hub. It is still dripping with the tire inflated, but it's parked on a slight side slope at the moment. I'll move the truck this weekend.

I'm studying the TMs to figure out what parts I need to order before I get in there, and there's one thing that is not clear to me from the TMs. The -24P does not appear to show an oil seal around the shaft of the axle. I have had leaking front axles on my deuces, and I recall them having inner seals around the axle shafts, but it's been too long since I've worked on a rear axle and I don't remember what is in there. One of the deuce axle seals I replaced really frustrated me until somebody told me the trick of pounding it out with a long bar from the other side of the truck. That worked like a charm.

Should there be an oil seal around the axle shaft, or is the gasket/RTV under the axle flange the only thing keeping oil inside when the axle isn't level?

I plan to service the bearings since their grease may be contaminated with oil, and I'll order new bearing seals before I dig in there. I'm just not sure whether I will also need a third seal to go around the axle shaft. Thanks in advance for the small clue that I'm missing.

 

[M35A2-AZ]

Nf6x, There is not a inter axle seal like the fronts.
All there is a inter and outer seal that fit on the wheel drum.
Not to bad of a fix, just heavy parts!!

 

[nf6x]

Thank you! Maybe the bearing seals are intact, the bearings didnt get marinated in oil, and it's just the axle flange gasket leaking? Well, I won't know until I get in there. If there's any imperfection in the outer seal, the oil probably had time to find it while the truck sat with a flat tire. I've serviced bearings before, and handling that heavy drum and hub assembly is the only part I'm not looking forward to.

Edited to add: The 500(?) pound tire and wheel probably won't be much fun, either. Maybe I'll check the outer bearing for oil contamination before I start moving the heavy pieces around.

 

[m16ty]

If it's just leaking around the flange, you may just have a bad flange gasket or it's not uncommon for the bolts to be loose. I'd check my bearings while I had the axle out also.

There is a gasket on the axle flange but RTV will work fine.

 

[nf6x]

The flange looks like it is presently sealed with RTV, and that's how I have usually sealed my axle flanges in the past. It usually works well, but sitting on a side slope with oil up against it for a long time is a tough test to pass.

Now that I think of it, I want to take that wheel off to swap it with the spare anyway, in case sitting nearly flat for a while weakened the sidewall from the creasing.

The crane hydraulic filter indicator says it needs cleaning. I haven't opened up one of those before, and I don't entirely trust the automatic shutoff valve, especially without a Soldier B to help. So I want to drain the tank first, and that'll let me check for gunk and run it through a spin on filter, anyway. So I may head out this weekend to get a couple of clean barrels to drain it into, plus other future uses. I think I would like the translucent white plastic kind, with removable heads to make them easier to clean.

But my main task this weekend is gathering up all of the bits that go with my M543A2, because I want to put it up for sale real soon.

 

[73m819]

If the 900 axles are the same design as the older 5t rockwells, they ARE designed as WET hubs, the mil. added a crappy outer seal to make them grease hubs, mainly to keep water out of the hub and axle when fording for a extended time. IF you are NOT planning a naval operation, wet hubs will work great, just leave off the outer seals, then the hubs will be like any big over the road truck, the wet hubs will run a LOT cooler then grease hubs. as long as the back hub seal and ware surface is GOOD, things WILL be fine, of course the axle flange to hub needs a good gasket of some sort,

 

[m16ty]

Ron, the M939 trucks use the same axles as the older 5-tons. At least I know all the bearings and seals are the same.

 

[Beerslayer]

If the 900 axles are the same design as the older 5t rockwells, they ARE designed as WET hubs, the mil. added a crappy outer seal to make them grease hubs, mainly to keep water out of the hub and axle when fording for a extended time. IF you are NOT planning a naval operation, wet hubs will work great, just leave off the outer seals, then the hubs will be like any big over the road truck, the wet hubs will run a LOT cooler then grease hubs. as long as the back hub seal and ware surface is GOOD, things WILL be fine, of course the axle flange to hub needs a good gasket of some sort,

This is really helpful. Thanks for pointing it out.

 

[nf6x]

Hmm, interesting. So, is it even a problem if some gear oil got past the outer bearing seal and got into the grease? I do not expect to ever ford the truck.

 

[M35A2-AZ]

If the axle is leaking I would think the grease is washed out of the bearings.
All the leaking rear axles I have seen have had the grease washed out.

 

[73m819]

If the axle is leaking I would think the grease is washed out of the bearings.
All the leaking rear axles I have seen have had the grease washed out.

Yes true, but NOW lubed by gear oil, a mess is in the hub now, but the bearing ARE LUBED, in fact gear oil will tend to WASH small bits of trash OUT of the bearing, trash in a grease hub tends to act like valve grind compound.

I just got done RErestoring the brakes on a restored m62 (5t wrecker), ALL 4 outer seals had died a LONNNNNNNNNNNNG time ago, the hubs had tuned into wet hubs, the rear seals were old, the ware rings were a bit worn, but still NO, I repeat NO leaks out of the rear seals, only the fine dirt that sticks to the axle right there as found on normal big trucks, on inspection, the bearings showed NO signs of pitting, lack of lube, heat, dragging, or anything else that would lead someone to think a WET hub hurt the bearing let-a-lone needing to REPLACE the bearings.
So with the above said, WHEN we reinstalled the rear hubs we went with the WET HUBS design, new rear seals/wear rings, paper axle gaskets (using grease instead of goop on the gasket) just did a build lube of the bearings. so far we have about 200 miles on the wet hubs, hubs are running COOL (a lot cooler then my m819), NO leaks.

One more thing, a axle flange leak is a axle flange leak, has nothing to do with a wet hub, dry hub, grease hub, what it has to do with is a VIBERATION in the rear some where that caused the bolts to loosen, on civi trucks this is why the axle flanges have those CONE LOCKS that set in the flange bolt holes to PREVENT the flange bolts from VIBERATING loose.

 

[wsucougarx]

subscribed.

 

[M35A2-AZ]

I like the wet hub idea!!!

 

[swiss]

Per Ron's direction did the wet hub as described and after analysis of the situation it is awesome

 

[nf6x]

Is it problematic if oil has gotten past the outer seal and washed out some/all of the grease, but the oil can't flow freely between the axle housing and bearings because the outer bearing seal is still in place?

Conversely, if converting to wet hubs, should any grease be used at all? Or should the bearings be cleaned of all grease and then wetted with gear oil at installation time?

 

[73m819]

"Conversely, if converting to wet hubs, should any grease be used at all? Or should the bearings be cleaned of all grease and then wetted with gear oil at installation time?"

WE build lubed the bearings, till the hub could fill, the OLD outer seal were lonnnnnnnnnnnnng worn out, when we got into the hubs, they were ALREADY working as wet hubs and had been for a long time, on the rebuild (RErestore) all we did was NOT install new outer seals,.

If someone wants wet hubs, I WOULD install NEW rear seals and wear rings because BAD seals DO NOT leak grease but WILL leak oil.

WET hubs WILL run a lot cooler because the oil draws away the heat from the bearings, then the total housing acts as a heat sink, GREASE hubs on the other hand WILL run very warm because the grease HOLDS the heat from the bearing AT the bearing.
I had the truck to 50 for a fair distance on the trip to the fuel deport and back, apon placing my hand on the rear hubs, checking hub temp. they were COLD, the front (grease hubs) were warm

AS MR.G said, you CAN NOT do the wet hub thing on the deuce rockwell axle because of the CRAPPY rear seal set up UNLESS you do some spindle machining

 

[73m819]

Is it problematic if oil has gotten past the outer seal and washed out some/all of the grease, but the oil can't flow freely between the axle housing and bearings because the outer bearing seal is still in place?

QUOTE]

If oil is where you say, it is ALREADY flowing, filling the hub, the bearings are being lubed

 

[erixun]

This is a timely thread for me as well, as I am ordering parts today to replace my rear seals that began leaking on the drive home.

If you get yours apart first, please post some pics to go along with it, sometimes the drawings in the TM's dont match in my eyes to what I am actually looking at.

If I get mine torn into first I will post some pics as well, from what I have heard even a first timer can do this job in about an hour or so.

 

[nf6x]

I wasn't planning to work on that hub this weekend before. But after the interesting direction this thread went, I may just reseal the axle flange and not worry about servicing the bearings just yet. So maybe I'll have a chance to take some pictures after all this weekend?

 

[73m819]

This is a timely thread for me as well, as I am ordering parts today to replace my rear seals that began leaking on the drive home.

If you get yours apart first, please post some pics to go along with it, sometimes the drawings in the TM's dont match in my eyes to what I am actually looking at.

If I get mine torn into first I will post some pics as well, from what I have heard even a first timer can do this job in about an hour or so.

If the rear seals started leaking, pull the axle vents BEFORE you take apart the hubs, if the vents ARE sticking and not releasing axle pressure, your seals WILL leak everytime, the ONLY place for the pressure to go. There is a bunch of threads on vents sticking and seals leaking