M931 right rear wheels not turning

[mbreg]

Hi, I've got an M-931 A2 that runs strong but recently have an issue with the rear 2 right wheels not driving. Has anyone had an issue like that? I have it on a lot where there's some pretty sizeable bumps/rocks, and one day when I put it in gear the 2 left wheels would drive while the 2 right ones wouldn't turn. I've tried in low gear to engage 4x4 and with/without front wheel drive engaged but still same effect. Its never been in low and in reverse (which the manual warns not to do).

Has anyone experienced anything similar?

thanks!
Mike

 

[dk8019]

Mike, to clarify, are the wheels locked up, or is power not transmitted through them to the ground?

 

[mbreg]

Mike, to clarify, are the wheels locked up, or is power not transmitted through them to the ground?

Good clarification, the right side wheels aren't turning at all, but I'm not really sure what the cause is.

 

[Rmtaunton]

Do you know how a differential works ?

 

[mbreg]

Do you know how a differential works ?

Sure, but with the 4x4 rear wheels engaged (engages automatically when shifted into low), the left wheels shouldn't spin while the right wheels don't turn.

 

[Rmtaunton]

Only the lightest or wheel and tire with least traction will spin or be powered if your in a slippery or off camber situation

 

[mbreg]

Only the lightest or wheel and tire with least traction will spin or be powered if your in a slippery or off camber situation

It is in an off camber situation, parked with right side slightly lower, and the front slightly uphill, but its never had trouble backing out of that spot before. With 4wd engaged (forward direction only), the left wheels shouldn't spin while the right wheels are stationary, which makes me think the right wheels are locked up somehow. Am I missing something about how the 4x4 works with these? Especially with the 6x6 engaged, it should easily drive out, but the 4 right rear wheels don't turn at all.

 

[mbreg]

I guess I could pull it back with my excavator and see if it behaves differently on flatter ground, but was hoping someone might have some experience with that situation and have an idea of something I'm missing.

 

[Rmtaunton]

If your stuck , and only have 1 wheel spinning on each axle this is normal operation of a differential, often turning the front wheels will shift the weight and traction and make the other spin or find a sweet spot where they are equeal in order for you to drive out

good luck

Robert

 

[Swamp Donkey]

You don't have lockers apparently so...with the weight on the right side and open differentials, only the left side is going to spin. This is because the left side has less traction. Just one of the downfalls of open differentials.

Both rear axles are always engaged, no matter if you're in low, high or 6x6. Flipping the dash switch for 6x6 just engages the front axle. If your in 6x6 with open differentials you are only guaranteed to have 3 powered wheels. If not in 6x6 you are only guaranteed to have 2. In the right situation all powered wheels can end up being on one side.

 

[mbreg]

Thanks Robert and Swamp Donkey, for some reason I thought the rear differentials locked when transfer case was shifted into low and 6x6 engaged, but looking back in the manual I'm not seeing anything about a locking rear differential. That would explain the situation pretty well.

 

[Rmtaunton]

No Problem but I would still try turning the front wheels while in drive 6x6 given it only works in the right conditions , but the good news is your truck is fine and the bad your still stuck lol

Good luck and keep on

 

[wheelspinner]

Are the tires "dragging" when you say not turning? Or is the truck spinning two tires but not the others with no motion? Makes a difference in diagnosis. If its the former, beat the drums with an 8 LB sledge hammer. If its the latter, exactly what Swamp Donkey said above.

 

[mbreg]

No Problem but I would still try turning the front wheels while in drive 6x6 given it only works in the right conditions , but the good news is your truck is fine and the bad your still stuck lol

Good luck and keep on

Thanks, I can deal with stuck a lot better than nonfunctional : )

 

[mbreg]

Are the tires "dragging" when you say not turning? Or is the truck spinning two tires but not the others with no motion? Makes a difference in diagnosis. If its the former, beat the drums with an 8 LB sledge hammer. If its the latter, exactly what Swamp Donkey said above.

Great tip wheelspinner (appropriate name), I haven't seen the right tires actually drag yet, but sounds like you've successfully dealt with that situation as well. I'll put the transmission/transfer in neutral and drag it down a few feet to flatter ground with the excavator and see if it was just the off camber position causing the looser wheels to spin. Pulling it a bit might loosen the wheels up as well if they've gotten moody from sitting for a few months.

 

[73m819]

Also a bob tailed 931 (tractor) has NO weight on the rear axles, the reason the truck moved with the front engage is this is where 90% of the weight is making it harder to spin the tires.

 

[goldneagle]

I might be wrong but i think the brakes are stuck to the drums. I have that problem when my truck sat a long time without moving. It may also be caused by a leaking spring brake. You can try caging the brakes on the DEAD side and beat the drums with a heavy hammer to release the stuck brakes.

 

[dilligaf13]

Ditto to the stuck rear brakes. The M931/932 are notorious for this. I think the rear drums being exposed to the elements allow them to stick easier than the cargo trucks and the lack of a weight, associated with cargo bed, make them harder to unstick afterwards.

 

[155mm]

Had the same problem with the brakes on my 931, left side, both rears would stick to drums, now I leave it hooked up to the trailer, not an issue with stuck brakes.... knock on wood.

 

[mbreg]

Well, I towed the 931 about 20' onto flatter ground last night with the excavator and the rear right 2 wheels dragged, so it does sound like the stuck brakes issue. Once on flatter ground I was able to drive it forward and backward slightly with front wheel drive engaged to see if the rear right wheels would loosen up but no luck, and daylight ran out on me so will have to try the other remedies next time I'm out there. Thanks for the suggestions on dealing with stuck brakes.