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How does the m1078 4x4 work?

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wyocyoteee

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New member here. I bought a m1087 and have converted it to a plow truck. Occasionally the 4x4 won't enguaged and I only have rear wheel drive.
What can I do to ensure I am in 4x4?
Thanks
Alex
 
porkysplace

porkysplace

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wyocyoteee said:
New member here. I bought a m1087 and have converted it to a plow truck. Occasionally the 4x4 won't enguaged and I only have rear wheel drive.
What can I do to ensure I am in 4x4?
Thanks
Alex
Click to expand...

Here is a link to the technical manuals .

M1078 TM's

Listed below are a number of the TM's for the M1078 trucks. To save them to your computer, right click, select "save as" m1078_TM 9-2320-365-10.pdf TM 9-2320-365-10 for the M1078 series trucks. m1078_TM 9-2320-365-20-1.pdf TM 9-2320-365-20-1 for the M1078 series trucks. m1078_TM...
www.steelsoldiers.com

You really should read this one ;
m1078_TM 9-2320-365-10.pdf
m1078_TM 9-2320-365-10 for the M1078 series trucks.
 
coachgeo

coachgeo

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wyocyoteee said:
...4wd? ...rear only
Click to expand...
there never is rear wheel drive only unless something veeeewy wong and bet you would go into limp mode before that happens. That truck is AWD and 4wd only.

on your 6x6 when you go into mode (aka 4wd)
. your two rear axles lock together making them both activated ....
. your front axle will get power just like any other 4x4.
. the rear set axles gets 50% power shared between the two (25% each) generically speaking
. the front axle gets 50% generically speaking

when in highway mode
. front axle gets 30% generically speaking
. rear axles(s) get 70% that will be shared between the two. rear axles... which one gets, what part of that 70% is "differentiated" by the differential inside Power Divider Box (that big chunk of metal gear case attached to middle axle { aka front axle of the rear pair}

there is so much weight on front compared to back I bet your just not slipping in front on either side so one wheel up there is powering along as happy as can be and the other is just following along just as happy.


Now if your opening post was a typo and you have an M1078 then above is almost all same.... just no rear pair of axles...... just one axle back there. In awd it gets 70% and 4wd it gets 50%
 
R

Ronmar

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AWD can seem like 2WD as it has a center differential so if a rear wheel can spin, ALL the torque can escape thru the rear diff and a single rear wheel. The center diff is geared so the rear end has a mechanical advantage(70% torque to the rear, 30% to the front) and unless you are loaded to give better traction to the rear it is most likely that a rear wheel will spin. you can spin just a front if the rear is on solid ground and the front is on ice.

To engage 4WD and lock that center differential you must press the "MODE" button on the shift control panel. then you should get one front and one rear wheel spinning as the axles are open differentials:)
 
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wyocyoteee

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Thanks Porkysplace. I downloaded the operato's manual.

I read up on the owners manual and tried using MODE and down shifting to 1st gear. I took it to an icy patch and put the plow into a snowbank. I'm reasoning that I should have 1 wheel on both axles spinning on the ice. I only had one spinning on the rear driver.

Is that normal or do I have something more I need to check.

Thanks
Alex
 
T

tennmogger

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I think the drop box provides power to the front axle by activating clutches by hydraulic pressure. Not talking about 1st gear which is gears, of course. Has anyone found any reference material on the dropbox 4wd clutches specifically?

If 4wd works sometimes and not other times (with the front axle being the failure to pull) then dropbox clutches might be slipping or the actuating hydraulic pressure might be too low.

Of course the main transmission uses clutches this way to activate/select gears so logic says the dropbox would operate the same way. Anyone who has activated MODE probably noticed, as I have, there is no detectable gear shifting, clunking, etc, as heard in a geared transfer case. Also there is no binding of gears as would be indicated by need to back up to 'unwind' the torqued up gears to get out of 4wd. Just press the MODE button and 4wd goes away smoothly.

I too have noticed that the front axle seems to vary in degree of pull in normal (non-Mode) operation. The 30% power to the front seems to be a 'suggestion' rather than a rule. Lubrication testing on my trans fluid has always indicated "high copper" on the two transmissions tested here. Maybe that is an indication of clutch wear-in? BTW, I use 4wd a lot too here on the farm, using an LMTV to pull implements in MODE.

My suggestion would be to rule out any driveline hardware problem first by using your 'snowbank test' and having someone verify the front driveshaft is not turning under power in mode. If the rear axle is driving but the front is not then the dropbox must be the culprit.

Allison Service could undoubtedly tell you what is going on. A trans fluid analysis (as by Blackstone) would be informative. I wouldn't work the truck much with slipping clutches.
 
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Ronmar

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What Tennmogger said. The center diff is a planetary differential. A planetary has 3 driven or drive points. The sun gear, the planetary carrier which holds the planetary gears that orbit the sun and the ring gear that rotates outside the planets. In this case I believe the transmission thru some fixed gears drives the planets/carrier. The ring gear is connected to the rear driveshaft yoke. The sun gear is connected to the front driveshaft yoke. The difference in gear relationship between ring and planets and planets and sun give you the 70/30 torque relationship that favors the rear

You dont feel or hear any clunking when shifting from AWD to 4WD because no gears are being shifted. The C7 clutch pack connects between the front shaft connected to the sun gear and a plate connected to the planetary carrier. When you select mode the controller tells the valve block to send hydraulic pressure to that C7 clutch pack which should lock the sun to the planets which disables/locks the center diff for a true 50/50% torque split.

As tennmogger said, slippery surface, plow against something solid and see if the front driveshaft spins. it probably wont, because if it did you have a front axle problem, but if that was the case the truck would not even move in AWD as all the torque would escape thru the problem in the front, just like it wont move in the test I mentioned above lifting one front wheel off the ground.

there are test ports on the bottom of the transmission for all the clutch packs and you can connect a high pressure test gauge to the C7 port to see if the valve block is sending pressure there when in mode should be a couple hundred PSI. The specific info for this test is in the manuals...
 
R

Ronmar

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snowtrac nome said:
the 30 / 70 split between front and rear is relative to weight in the rear if the rear axle is loaded heavyer than the front power will flow to the front first I have experienced this several times on the ice.
Click to expand...
Exactly, the torque will escape to whichever wheel has the least traction relative to the others In AWD.
 
MrMikey4026

MrMikey4026

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Having recently been very stuck with mine in the backyard. Without using the mode function, it only spun one rear. Using the mode button, it spun one front and one rear leaving me still stuck. I had already selected first gear before I used the mode button. I really need to get the CTIS working!
 
coachgeo

coachgeo

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MrMikey4026 said:
Having recently been very stuck with mine in the backyard. Without using the mode function, it only spun one rear. Using the mode button, it spun one front and one rear leaving me still stuck. I had already selected first gear before I used the mode button. I really need to get the CTIS working!
Click to expand...
and or a locker
 
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