I have AWD but not 4WD


New member
i can not get 50/50 4x4 when i press the mode button.

I picked up a m1079 a week ago and drove it 500km home. Before i left everything seemed to work but i could not get the 4x4 to engage. I checked and topped up any fluids that needed it (wasn't much of anything) before i left, everything ran great. since i have been home i still have not been able to get 4x4 to work.

In regular D i have all 7 gears ( even forcing it in to 1 by down shifting with the arrows) and R. when i push mode it now limits me to 1 to 5 and i can get all gear no problem but i have no 4WD it just stays in AWD. the drive shaft spins when i drive but not once the rear rend spins out. I left it in gear when stuck going up a icy hill with mode on and just one back tire spun ( i got out of the truck well in drive to see for my self). the front drive shaft stopped spinning and front tire did the same (no front drive shaft no front wheel spin). so other than the transfer case not locking everything else works as it should.

I did as much reading and searching as i could but could not find much.
this is what i have tried so far,

- drain the diesel oil out of the transmission and transfer case and replace with dex 3 ATF(i am on the second flush and will be change the fluid one more time as well as the filters). the drain plug for the transmission was clean, the drain plug for the trans case had a few metal flakes.

-i pulled the scavenge pump line and cleaned the metal filter ( there were a few small metal flakes at the top of the screen) .

-i pulled the actuator and it was clean and looked fine, wires and plugs looked good as well.

- looked inside t case and everything looked good with no signs of wear.

-i checked all the plugs on the transmission and transfer case, they all looked clean and in good shape.

-i checked for code on the shift module in the can, nothing.

- the shift controller was sent out to some were in Texas to be rebuilt (should be brand new)

what is my next step? this has to be fixable but i am not sure were to go next.

could they have messed up programming the controller?

do i have bad relays? i hear something in the passenger side dash click when i hit mode, but it there more than on relay that needs to fire?
i will take any help i can get, thanks


Well-known member
Port angeles wa
I don’t recall hearing any click when I select mode, it should all be in the transmission. I guess the next thing you could look at is wether it is sending any pressure to the center diff clutch pack. There are pressure test ports on the bottom of the trans and transfer for monitoring the clutch pressures, and the specified pressures are listed in the Allison md3060/3070 troubleshooting guide. Don’t know if that manual is on this website, but if you google TS2470EN you will find several places to download it as a PDF for free...

No C7 pressure in mode means it may be a non functioning valve or programming. Pressure at the C7 port and it is most likely the C7 clutch pack is bad... most of the clutch pressures run around 200PSI if I recall correctly, but they are listed in that manual...
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