M-1083 just front tires spin in mud not rear

new to ss just bought 1083 and had it in the mud yesterday hooking up to my 989q1 trailer and noticed when in reverse pushing against the trailer just both front tires were spining .DIDNT SEEM RIGHT ANY IDEAS

Welcome to the site. You need to engage "Mode" on the WTEC controller to lock the inter-axle differential and the transfer case.

Maybe your passenger side rears were spinning and you just couldn't see? Press the Mode button on the the shifter pad to lock the transfer case, light should stay solid. The LMTV / MTV series are similar to the M939 trucks, they power the rears by default and need some operator involvement to power the front axle. If I misread what you posted, I'll try to provide some advice.

Yeah what NDT says.... little more detail.

if your in All Wheel Drive.. aka.... normal Hwy Mode..... then it will send most power to all power to the slipping axle. Think of tranny also acting like an axle differential, between front and rear drive systems. AKA- Tranny on these trucks also acts like a differential between tires...but instead it sits between front and rear drive systems.. If you put it in 4wd mode... all the FMTV's will then go into what most consider normal 4wd. (50/50 power send to front and rear drive systems) On the 6x6 as NTD says.... this also locks the two rear axles to both get powered. (normally only one with most slip gets power cause that two has a differential between the two axles.. ) yup..... there is essentially 5 differentials in these MTV's

sandcobra164 said:

Maybe your passenger side rears were spinning and you just couldn't see? Press the Mode button on the the shifter pad to lock the transfer case, light should stay solid. The LMTV / MTV series are similar to the M939 trucks, they power the rears by default and need some operator involvement to power the front axle. If I misread what you posted, I'll try to provide some advice.

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5 ton FMTVs the front pulls and the rear rear pulls by default. The front tandem is a power divider like a normal commercial truck that only engages in mode for low range Which I think adding a power divider switch would be beneficial than always having to be in low range to use it. Especially since the FMTVs won't even climb my trailer in high range since the front tandem doesn't pull.

simp5782 said:

5 ton FMTVs the front pulls and the rear rear pulls by default. The front tandem is a power divider like a normal commercial truck that only engages in mode for low range Which I think adding a power divider switch would be beneficial than always having to be in low range to use it. Especially since the FMTVs won't even climb my trailer in high range since the front tandem doesn't pull.

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This idea has been batted around.... that one of the two rears just tags along till activated.... by mode. This has been disputed cause well.... there is a differential in there...... if one was only set to be active or inactive.. you would only need a device to disengage/engage one of the two rears... there would be no need for a differential

Here is a good read that seems to point toward above

https://www.quora.com/Which-axle-drives-a-tandem-truck

Each axle are open differentials I would think you would only spin one wheel per axle.

sandcobra164 said:

Maybe your passenger side rears were spinning and you just couldn't see? Press the Mode button on the the shifter pad to lock the transfer case, light should stay solid. The LMTV / MTV series are similar to the M939 trucks, they power the rears by default and need some operator involvement to power the front axle. If I misread what you posted, I'll try to provide some advice.

Click to expand...

This does not seem right. It is AWD and powers all wheels all the time by default, but it is a 60/40 split with more torque going to the rear. The mode button locks the center diff so it is a positive 50/50 and both driveshafts will turn.

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m-35tom said:

This does not seem right. It is AWD and powers all wheels all the time by default, but it is a 60/40 split with more torque going to the rear. The mode button locks the center diff so it is a positive 50/50 and both driveshafts will turn.

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welll..... sorta when it comes to the "all the wheels all the time".... if not mistaken AWD Tcase also acts like a differential to a point so if front tires begun to spin...... it would NOT send anything to the rear wheels...... it would all go to the front wheels.

It is supposed to be a 40/60 power split and in regular mode the two driveshafts can spin at different speeds so you dont get binding when turning on hard surfaces. If the front axle has no traction in regular drive mode the rears will not spin. Figured this out one day when unloading from a step deck. Once in "mode" the truck drove right off.

Suprman said:

If the front axle has no traction in regular drive mode the rears will not spin.

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Open differentials apply the power to the wheel with the least traction. So on a single axle, it goes to the wheel that is loose, not the one with traction. If you put another open differential in between the two axles, it too sends the power to the output (the axle) with the least traction, then that axle sends the power to the wheel with the least traction. The result is that the engine power goes to the single wheel with the least traction out of all four, in an All Wheel Drive (AWD) system with an open differential in the center (and open differential axles).

The LMTV does not have an open differential in the center, but instead has a more complicated differential mechanism which allows torque to be split at a set ratio (in this case 60 rear : 40 front). Theoretically, you shouldn't be able to have a situation where only one axle has spinning tires (if nothing is broken/malfunctioning). That said, due to the complex nature of these design problems and solutions, some of the differentials that do this have circumstances that can cause them to not function correctly. For example, some require at least some resistance on the loose output in order to kick off the reaction, and you'll see suggestions made like lightly applying the brakes to provide a little resistance needed to engage the torque vectoring to the high-traction output. This kind of thing happens if one output (wheel for an axle, or axle for a center diff) is on ice, which is essentially a zero-friction surface - it won't have enough resistance to engage the capabilities of the differential.

When in Mode, the center differential is completely disengaged (e.g. "locked"), and both front and rear driveshafts are rotating at the same speed, mechanically locked together. Each axle, in its stock configuration, has an open differential, so while both axles are being driven, each will still be routing power to its wheel with least traction... but at least you'll have two wheels (one front, one back) spinning!