Stemco Seals

An older gentlemen at work keeps telling me my truck has "wet bearings" in my 5 ton. I've explained to him a few times that they are only "wet" if the outer seal has failed and the inner doesn't do much to keep oil off the brakes. He explained to me that there is a way around the Army's design in way of a company called www.stemco.com He claims they can take the part number from the existing inner seal and make a race for the hub and a seal of Texas leather that will keep the oil in. We could discard the outer seal and run "wet bearings". I'm game for that as I noticed about a 20 degree drop in hub temperatures when my deuce was leaking due to a defective outer seal and had oil in the hub. I've viewed posts on the Deuce subforum saying such a thing does not exist but I'm curious to know if anyone has pursued this for 5 tons. I'm skeptical as well but if it's good for the goose, it might be good for the gander. The company caters to Class 8 Over the Road Trucks from what I have read.

I volunteer you as the guinea pig!

Oil bath wheel bearings are the norm on the M915 series, FMTVs, and every class 8 truck since the 50's. For the life of me I can't understand why the military kept grease lubed bearings on deuce and 5 tons for so long, must be a tradition thing like taps and reveille. I run Stemcos on my 915, they are solid, as good as CR, Federal etc. Would be nice if someone did the legwork to see if the old Timken-Detroit/Rockwells can be converted.

The inner seal on the M939 series is a regular oil seal. When I pulled a hub on my M929 to service the brakes the hub was full of gear oil. There were no external leaks. I saw the inner seal was an oil seal and remembered an old post Ron (73m819) had made about wet hubs in the 5 tons and PM'd him. He said he left the outer seal off. I left the outer seal on (because it acts like a washer) but notched it so the oil could fill the hub and put the hub back on with the oil in the hub. All of the hubs run in the 100~120 degree range. Much cooler than my Deuce hubs did after I serviced them.

Here's a picture of the oil filled hub before I reinstalled it. I thought I had a picture of the inner seal but I don't.

I'm going through this right now on my 925A2 because I bought the back half of a 923A2 to make a matching trailer and I am gutting the axle housing drive contents to lower weight and rolling resistance. I believe because of the CTIS (A2 only), the rear axle hubs run gear lube for the outer hub bearing (no outer grease seal), and grease on the inner. The A2 hubs (front and rear) also have an additional 2 seals inside the hub for the CTIS air transfer path from the spindle to the hub. Because of this, even if the outer bearing is gear lubed, the inner would need to be grease, as there is no path for the gear lube to traverse through the hub to the inner bearing. So, I think on A2's, they half way do this already, in the rear only. The fronts are still grease on inner/outer, obviously. On A1's and first gen, as long as the inner seal is in good shape and holds, I believe others hear have converted to oil lube rear with no issue. Obviously if the inner seal leaks, there goes your brakes for that wheel. I just finished a 300 mile run on my 925A2 @67mph the entire way, and my front hubs were as cold as the rim itself, and the rear hubs were just barely warm, maybe just under 100F. I only touched the brakes once at the exit ramp.

It would be hard to make the front an oil setup because the oil would run back the spindle and into the knuckle. I don't see why you couldn't make the old style 800 and 900 rears oil bearings if you can find the right seal. for guys that have eliminated the ctis you could pull the ctis seals out of the hub and make both bearings oil. the factory A2 seal is a stemco style seal. But as said once you loose a seal there goes the brakes and mess not fun to clean. the old style front could possibly be made oil if you used the outer rear seal on the front and had a way to get oil into the hub between the bearings. We run the outer seals on all the axles in the mud truck because if mud gets into the bearings that seal keeps it from getting into the knuckle or housing or if you tear a knuckle boot and the mud goes int through the spindle it'll keep it out of the bearings. Just not sure if that seal would hold oil into the hub though.

That is the same reason they supposedly kept grease and outer seals in the A1's and first gen, for water fording. Same as your mud intrusion.

less parts with goo or water the less work to clean. lol

In the old fleet I maintained as the fleet manager and the now current one I manage....I only use Stemco products for their warranty and support. Cost & durability.
If you have old existing part numbers and need help converting Joe pm me and I will get you a contact # to assist you.

I just repaired my M932A2 Ctis on one wheel. As it turned out one air seal had moved in the hub and was not hold air anymore.
But when I took the hub apart I found that there was not a seal like the A0 & A1's outer oil seal, only the two air seal and the inter seal. So I guess the outer bearings get oil and the inter bearings are grease.
The TM says to use GAA on the bearings, but without a outer seal the grease gets washed out.

correct A2's are oil on the outer

M35A2-AZ said:

I just repaired my M932A2 Ctis on one wheel. As it turned out one air seal had moved in the hub and was not hold air anymore.But when I took the hub apart I found that there was not a seal like the A0 & A1's outer oil seal, only the two air seal and the inter seal. So I guess the outer bearings get oil and the inter bearings are grease.The TM says to use GAA on the bearings, but without a outer seal the grease gets washed out.

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Thanks for the confirmation and pic. Even todays over the road trucks, they say to grease them some on install, as it takes some time for gear lube to reach them once rolling.

IIRC, Try a Stemco 2110. They work on most class 8 trucks rear drive axles and trailers. i could be wrong but that's what I believed we used when I worked at Western Star Trucks.

M35A2-AZ said:

I just repaired my M932A2 Ctis on one wheel. As it turned out one air seal had moved in the hub and was not hold air anymore.
But when I took the hub apart I found that there was not a seal like the A0 & A1's outer oil seal, only the two air seal and the inter seal. So I guess the outer bearings get oil and the inter bearings are grease.
The TM says to use GAA on the bearings, but without a outer seal the grease gets washed out.

Click to expand...

On that A2, what size are those nuts? I know they are in the 4 inch range. I need to get the socket before I tackle this job.

NDT said:

Oil bath wheel bearings are the norm on the M915 series

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Just the M915A1 and the front axle on the M915. The M915 rears, front, & rears on the 916, 920, etc are greased hubs.

The unitized style seal SKF (CR) PN is 47660 and the National PN is 370051A. I have had good luck with both of these in the drive axles (M936). If you haven't installed this type of seal before, read the manufacturer's install procedures...this style of seal is not installed like the steel cased lip type. I cannot say how these seals will perform during fording ops, but they are definitely far superior to the old style for keeping gear oil in the hub.
Regards, Bob