M939 series rear axle seals

[nf6x]

Thanks for pointing out the axle vents!

Mine may still be fine, since I found last night that the axle flange bolts were loose on the leaking hub.

 

[erixun]

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

Thanks!!! I have not checked those... just assumed they were working as when I checked the diff levels I had no "pressure release"- and saw the fluid that had leaked out of the seal area.

Now if that was/is my problem, I hope it did not ruin my seals- just tweaked them enough for the pressure to release and went back to normal.... ha ha... I am not that lucky, murphy gets me some times.... on the other hand I did just order $180 worth of parts, so maybe he will get me that way... by making those parts not needed.


And I did not/ do not intend to hi-jack this thread.... just hitch hike a little.

 

[m16ty]

We always pack (with grease) our oil hubs on civilian trucks. It takes a little time for the oil to get there from the pumpkin, in the mean time your bearings are running dry if not packed. The grease and oil mix won't hurt a thing.

 

[73m819]

that is what we did, a build lube till the hubs filled, you would be surprised how fast that they fill.

 

[seano11]

At the moment I'm running 2 wet and 2 greased hubs . The greased hubs run at 120to 130 on the highway. The oiled ones run at 30. I'll be switching my greased hubs to oil next set off. I hope my writing has improved for everyone

 

[erixun]

I found these pages in the new TM 9-2320-272-23-3 and they are the diagrams / instructions on replacing the rear hubs- which also show the rear seals....

View attachment TM 9-2320-272-23-3 Field Maintenance Rear Hubs Replacement (M939A2).pdf

Hopefully this worked. I can open it on my computer.....

 

[swiss]

Here are some pictures of the rear with the hubs off. I did not get any pictures of the seals after we setup the rear seal on the hub.

A couple of things to note when installing the wear ring.

1.) boil water and put the wear ring in for one minute. Be careful not to overheat as it gets soft
2.) I used a PVC pipe I think 3" with a flange that perfectly fit the wear ring and allowed me to put a piece of wood on the end and then drive the wear ring on evenly. Once heated it will deform easily. You have about 5 minutes to work them on and then it gets tough. One got crooked an had to be cut off with the grinder and start over. Get an extra wear ring or 2.

 

[nf6x]

I sealed up my axle flange today. The lock washers looked a bit sprung, so I replaced them. Here are some pictures. I used some Permatex RTV from Pep Boys that claimed to be particularly good at resisting gear oil.

I cussed at the axle for a while trying to get it to line up with the splines in the diff until I figured out that I wasn't tilting it far enough by hand. Then I grabbed the monkey wrench from the wrecker's BII, clamped it on the top of the flange, and used it to lever the axle into place. It's been long enough since I've had an axle apart that I forgot the obvious stuff.

 

[lakeydna]

M939 and M809 have similar axles, can the front caps interchange?

 

[Tow4]

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

Bringing back an old thread with a new question.

Ron, what did you do with the outer seal when running as a wet hub? Did you leave it out or put the old one back in? It seems like the seal doubles as a washer between the hub nut and the bearing.

 

[Suprman]

I have diff oil coming out my hub. I looked at the TM it was a little confusing to me on which seal separates the gear oil from the grease. I could just do what Ron recommend with the wet hub. But my truck is an A2 with ctis. Will diff fluid get into the ctis system if the hub is full of it? The truck is a 2011 rebuild that had been stored at FT MCCoy in WI. The axle vents look ok but could have been frozen up in the cold of WI.

 

[HDN]

I have diff oil coming out my hub. I looked at the TM it was a little confusing to me on which seal separates the gear oil from the grease. I could just do what Ron recommend with the wet hub. But my truck is an A2 with ctis. Will diff fluid get into the ctis system if the hub is full of it? The truck is a 2011 rebuild that had been stored at FT MCCoy in WI. The axle vents look ok but could have been frozen up in the cold of WI.

View attachment 553394

I know this is an old thread, but I've been looking up stuff about axle seals and wet bearings and couldn't let this question go unanswered. If there's oil in the hub, it will get into the CTIS components and gunk things up. That leads to wheel valves not functioning correctly. If a wheel valve fails open due to the gear oil gunk, the tire may go flat. My M35A3 had gear oil leaks in both rear axles and the oil got into the wheel pipes and valves from the hubs.

I'm not sure there are any modern truck axles that have both wet bearings and CTIS. I can imagine how one may design such an axle, though.

 

[Jbulach]

I know this is an old thread, but I've been looking up stuff about axle seals and wet bearings and couldn't let this question go unanswered. If there's oil in the hub, it will get into the CTIS components and gunk things up. That leads to wheel valves not functioning correctly. If a wheel valve fails open due to the gear oil gunk, the tire may go flat. My M35A3 had gear oil leaks in both rear axles and the oil got into the wheel pipes and valves from the hubs.

I'm not sure there are any modern truck axles that have both wet bearings and CTIS. I can imagine how one may design such an axle, though.

IIRC this is NOT correct for the M939a2 as for which the thread is titled. You should be fine running the outer on an M939a2 in an oil bath but would still need to grease the inner bearing due to the CTIS seals blocking the path between the bearings. Also I did not reread this old thread.