M1078 4x4 non existent

[Suprman]

Does the trans still have a low voltage error. If so clear it. See if it comes back. Take a digital multimeter at the posts left side of the power panel and measure the 12 and 24 volts with the truck running and see what they actually are. Low voltage will cause all kinds of issues.

 

[pangea]

Many lmtv owners do not know this but there is a steel mesh filter in the transfercase where the scavenge pump hose attaches to. The scavenge pump mounts on the right side of the transmission. Clean this filter or lose youre pump, transfercase and trans$$$. Pull the shift module on rear of tcase and check for any debris. Flush out from filter /hose hole down. Check you're rear output speed sensor for metal particles and clean. The rear output speed sensor is $595.00.

 

[pangea]

My 4wd was not working till I cleaned out my filter of metal particules. The module had small bearings and parts of the bearing races stuck in it. Now 4x4 "mode" works great! If I could only get rid of that grinding sound. Lol

 

[Btwedel]

Ok .. gonna have to do some more research and check that screen ... thanks guys , by the way this is an awesome forum .. every one has been super helpful. . Thanks

 

[Suprman]

Learn something new every day. Number 7 in the pic. If you have metal and bearing parts caught in the filter I think your transmission is on borrowed time though.

 

[Jericho]

The small bearings and metal particals are an old school BIT code device "BS in Transmission" It wont light any code enunciators but it means the same thing, Be on the look out for a rebuilt!

 

[Btwedel]

Well I looked in the small filter on the scavenge line and wasn't just a lot there but some small flakes and a few small shaving from some where cleaned it all up and, still no 4x4 ... if there is debris on the shift module can it make it do this ? Haven't had time to pull it off yet...

 

[Suprman]

Are there any error codes stored?

 

[Btwedel]

No. Since I grounded the ecu housing and cleaned and greased the connections under the truck , no codes...

 

[Suprman]

I know the wtec3 does an "impedance sense" of the solenoid coils across the wire harness. Not sure if the wtec2 does as much. Does the truck go into low range and drive like that?

 

[Btwedel]

Yes .. when you turn mode on it won't let it shift above 5th gear...if that's what your talking about?

 

[Suprman]

Yes thats supposed to happen. If you put it in mode then in drive, press arrow down until 1 1 is displayed then you will be in low range. Its a very low gear. See if it works.

 

[Btwedel]

Yes lo gear works ...

 

[Suprman]

See if you have 4x4 in low range then

 

[Btwedel]

Gonna try to get the shift module cleaned up yet and then scratch my head somemore...

 

[Suprman]

If it shifts thru the gears chances are the shift module is ok. More likely a transfer case issue with your symptoms.

 

[Btwedel]

Yeah I'm a lil suspicious I've got internal problems... if a wire was broken it would thro a code wouldn't it ?

 

[Suprman]

In my experience just about anything will throw a code. If you put it in normal drive and the system cannot apply any power to the front axle it will usually not go anywhere. You have to put it in mode in a front loss of traction situation. So its weird that the truck drives when not in mode if you really dont have any power applied to the front.

 

[Btwedel]

Well I've tried low gear with mode on ... no 4x4 ..I don't know exactly what to do ... can someone explain to me how these transfercases are constructed inside ... how do they transfer 30 percent forward and 70 percent to the rear ..and mode on becomes 50/50 is there clutch packs in there or is it done with worm gears ??? I am at a loss ...

 

[Suprman]

Clutch packs. Probably a bad transfer case then. Your local allison dealer can make a definitive diagnosis. If you can get the trucks free thru the gov agency giveaway program just get another one and use one for parts.