M929A1 Rear Axle Heat Difference

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
Thought I would ask for diagnoses advice, but I will search the forum for any threads related to possible cause for excessive heat difference on one hub. My right rear hub is much hotter to the touch others. All others are normal. At this time I have the axle removed, ready for the inspection of bearings, brakes etc... At first glance, everything looks o.k. on the inside with axle removed. Going to start inward in a few minutes to see if I find anything unusual. Got this truck with 17 hrs on it. The best deal in my lifetime. It was referbed in 2010. As far as I can tell everything is pretty much factory fresh. Engine started breaking in at about 35 hrs. Probably topped out at 60 hrs. I've got 83 on it now. Needs an oil change.

Anyway, just working down a list of things that need to check out or fix after 80 hrs of break-in. Noticed that the right rear hub was running hot to the touch. Maybe a brake pad dragging?

If anyone has and suggestion please sound off. I'll check back in awhile.

20170310_091250.jpg
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
There is no visible grease on the outer bearing? Dang? I guess the only thing keeping this hub going was the gear oil that spilled out when I remove the axle. No sign of any burning or metal residue. I've got to review the 939 TM for hub removal. I have done 800 series with hydraulic brakes, but nothing with air brakes. I guess I need to check them all and repack bearings as needed. We have 4 days of rain with 100% humidity here, so ignore the surface rust setting in.

20170929_180617.jpg
 

simp5782

Feo, Fuerte y Formal
Supporting Vendor
9,019
1,741
113
Location
Memphis, TN
Make sure your brakes aren't dragging first. Air the truck up. Chock the wheels and jack up that one axle and spin it. Could be a stuck wedge causing heat with the brake dragging. Pull each bearing out and use your air blow gun and spin the bearing with air and listen for excessive noise. You should hear the whistle and whine while you hold it in your hand. You will feel any drag or problems in your hand.
Check for putting in the bearing and races as well.

They are wet bath bearings. Only gear oil is in there. The fronts get grease though.
 
Last edited:

doghead

4 Star General /Moderator
Staff member
Super Moderator
Steel Soldiers Supporter
26,195
844
113
Location
NY
Bearings preloaded too tight or hard(aftermarket) oil seal.
 

74M35A2

Well-known member
Steel Soldiers Supporter
4,108
166
63
Location
Livonia, MI
Bearing preload needs to be a pinch loose, actually. On a semi-truck, Timken recommends the hub be able to slightly click when pushed straight in and out. This is because as the bearing heats and expands, that free clearance then becomes near zero.

I think a2's w/CTIS run no outer seals, so the outer bearing would be oil lubed. Others here will know better. A1's such as yours, not sure.

It is highly recommended by all bearing makers to never spin a bearing by compressed air. It can greatly overspeed and fly apart.
 
Last edited:

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
Wow! So they are oil bath... So does differential oil travel down the axle shaft? I guess my question is... how does the oil move out to the hub and bearings?
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
There is an outer seal. Everything looks the same as my M818. Will it hurt to lightly pack this side with grease to see if the temperature goes down? I mean very light application.
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
They did not seem to be too tight. I assume you set the bearing tension the same way you do on the 800 series truck? I'm haven't gotten that far in the TM on hub & bearing maintenance for the 939 series. I've read the brake PM, so that is the first thing I will check in the morning. Should I pull this hub regardless and check the bearings? I do not have any sign of seal failure. I assume that there should be plenty of oil in the drum cavity when/if I pull it?
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
I guess I have to remove the rear propeller shaft to isolate and spin the rear hubs? I'm changing out tires, so I have tires off on both sides of the rear axle.
 

74M35A2

Well-known member
Steel Soldiers Supporter
4,108
166
63
Location
Livonia, MI
I thought a1's were outer seal. This means the inner and outer bearings are grease lubed. I really should check the manual instead of advising by the seat of my pants, I have never had mine apart.

If both sides of one axle are off the ground, you should be able to spin one hub and the other rotates the opposite way, unless it has a locker diff in it.
 

simp5782

Feo, Fuerte y Formal
Supporting Vendor
9,019
1,741
113
Location
Memphis, TN
Be quiet rookie and go back to polishing your winnebago engine. It is past august and we are all still waiting.

Only outer seal is the gasket for the outer shaft where it bolts to the hub. The bearings get plenty of oil thru 3rd member movement. You should have leaked a good bit when you pulled the shaft. It doesn't take much oil. Putting grease in there isnt going to hurt.

Preload is the same as an 809 series.

Did you actually infared temp gun the hub? Simply feeling hot doesnt mean anything. Hubs can be 90 to 200. Mine were at 189 earlier towing a load

With your low hours your truck isnt driven much so a stuck wedge makes more sense to me.

Sent from my SM-G935P using Tapatalk
 

red

Active member
1,990
7
38
Location
Eagle Mountain/Utah
Be quiet rookie and go back to polishing your winnebago engine. It is past august and we are all still waiting.

Only outer seal is the gasket for the outer shaft where it bolts to the hub. The bearings get plenty of oil thru 3rd member movement. You should have leaked a good bit when you pulled the shaft. It doesn't take much oil. Putting grease in there isnt going to hurt.

Preload is the same as an 809 series.

Did you actually infared temp gun the hub? Simply feeling hot doesnt mean anything. Hubs can be 90 to 200. Mine were at 189 earlier towing a load

With your low hours your truck isnt driven much so a stuck wedge makes more sense to me.

Sent from my SM-G935P using Tapatalk
Aint the a1's the same hubs as the older m939, m809, and m54's? If they are then both bearings on all axle hubs are greased, not oil bath. And there is an outer seal that goes between the outer bearing/inner hub nut.
 

simp5782

Feo, Fuerte y Formal
Supporting Vendor
9,019
1,741
113
Location
Memphis, TN
Aint the a1's the same hubs as the older m939, m809, and m54's? If they are then both bearings on all axle hubs are greased, not oil bath. And there is an outer seal that goes between the outer bearing/inner hub nut.
Last one i took apart was an m54 series and i don't remember an outer seal. I dropped a set of 809 axles off in Georgia on Wednesday and with the shafts pulled on them i could see the outer bearings.

Unless it was just a moment that my adderral wasnt working and i saw that dang squirrel

Sent from my SM-G935P using Tapatalk
 

74M35A2

Well-known member
Steel Soldiers Supporter
4,108
166
63
Location
Livonia, MI
Isn't it fun when nobody wants to check the manual? If I look at there is an outer seal, you'll need to sing the "I'm wrong" song Simp.

Poster is on the right path of being concerned and investigating. One rear should not necessarily be hotter than other rears at any given time. If all cool or all warm, then OK. One warm and 3 cold, that's a flag.
 
Last edited:

red

Active member
1,990
7
38
Location
Eagle Mountain/Utah
Last one i took apart was an m54 series and i don't remember an outer seal. I dropped a set of 809 axles off in Georgia on Wednesday and with the shafts pulled on them i could see the outer bearings.

Unless it was just a moment that my adderral wasnt working and i saw that dang squirrel

Sent from my SM-G935P using Tapatalk
https://www.bigmikesmotorpool.com/c...ts/5-ton-outer-hub-seal-m54-m809-m939-7413447

Time to warm up them vocal cords. Besides the a2 all hub bearings are supposed to be greased.

Sent from my XT1585 using Tapatalk
 

Swamp Donkey

The Engineer
Steel Soldiers Supporter
1,438
61
48
Location
Gray, GA
Nomenclature correction....

So we have the two great 5 ton race truck builders in here but we can't figure out whether the hubs are grease or oil? For shame...:mrgreen:

So where does that leave us? Well let me see if I can ass-ist.

The rear hubs are originally grease lubed. There is an inner and outer seal on the A0/A1 trucks. If the outer seal leaks then gear oil will travel to the bearings. This is fine, and how I run my truck, AS LONG AS the inner seal is good. If the inner seal leaks then you end up with oil in the brakes.

So, in your picture Jaws4518, there is no grease in there. You say the seals are good so this would mean no oil either. That looks pretty dry to me. I think someone forgot the grease at rebuild. Wouldn't be the first time someone found this problem. Did any oil come out when you pulled the axle?

Take your pick, grease or oil bath. Both are fine. If you choose oil bath just make sure your inner seal is good so you don't soak the brakes. I've been running mine like this for about 2 years now. The bearings don't care what they're lubed with...oil, grease or a mix of both.
 
Last edited:

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
I concur. About 1/4 cup of oil came out when I pulled the axle flange off. There is no visible oil leaking into the brake drum. Both seals are good. I'm not taking any chances. Going to pack those bearings all the way around.
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
10/4 on that! This truck sat for years after the depot overhaul. I felt like the best thing I could do is run it and see if any problems surface during first 100 hours or so. How is oil maintained in the hub cavity? Obviously, it comes from the differential and flows outward. If the differential oil gets too low, we've got a serious problem. Right? Oh, the gear oil look nice and fresh.
 

jaws4518

Member
Steel Soldiers Supporter
141
1
18
Location
Abilene, Texas
There is an outer seal. It goes against the outer bearing. It's not a "discard" or throw away part unless it is damaged. If the other hubs have grease, then someone forgot to grease this one.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks