Transfer case help….M1078 2001

[Xengineguy]

Hi everyone I’m again working on my Lmtv. The problem of the day is the transfer case doesn’t engage 50/50
when mode is selected. However it does when I select 1st gear. I checked the scavenging screen, looked real good.
A few bits of plastics or gasket material. I am going to check c7 clutch pressure in both cases. If I lack c7 pressure
in mode I’m going to need some more info. Is the c7 solenoid in the transfer case or on the valve body? I have
multi meters and lab scope to check voltage/waveform. What should I be seeing in mode? Which pins or
terminals? Thanks. Mike

 

[Ronmar]

Hmmm. Engages in 1st, but not in mode... thats weird as the signal comes from the same place.

first off, how are you determining that it is locked or not?

The center dif valve is in the transfer. The signal for it as well as output speed sensor run thru a cannon plug on the front side of the transfer case.

 

[Xengineguy]

I jack the one wheel up put it in mode and one wheel spins (rear). Put it in first and it will drive off the jack no problem.
I know it’s a little different?? I will test pressure on c7 to verify what I think is happening.

 

[Ronmar]

Well thats weird. I suspect if it were a pressure issue it would have issue engaging in 1st and mode, but since it engages in 1st and NOT in mode, this almost sounds like a programming issue… your gear range drops to 5 when you select mode right?

 

[Skyhawk13205]

Hi everyone I’m again working on my Lmtv. The problem of the day is the transfer case doesn’t engage 50/50
when mode is selected. However it does when I select 1st gear. I checked the scavenging screen, looked real good.
A few bits of plastics or gasket material. I am going to check c7 clutch pressure in both cases. If I lack c7 pressure
in mode I’m going to need some more info. Is the c7 solenoid in the transfer case or on the valve body? I have
multi meters and lab scope to check voltage/waveform. What should I be seeing in mode? Which pins or
terminals? Thanks. Mike

The valve for mode is in the transfer case.

looks like it should be pins B and A on the transfer case connector.

 

[Suprman]

I would swap the tcm see if thats the issue. Post a pic of your tcm label

 

[Xengineguy]

Well thats weird. I suspect if it were a pressure issue it would have issue engaging in 1st and mode, but since it engages in 1st and NOT in mode, this almost sounds like a programming issue… your gear range drops to 5 when you select mode right?

Yes it does.

 

[Xengineguy]

The valve for mode is in the transfer case.

looks like it should be pins B and A on the transfer case connector.

Thanks!

 

[coachgeo]

Thanks!

connector problems have been reported too.... both the connectors under trans pan.... and connectors on the outside of trans as well as at TCU.

 

[Xengineguy]

Ok I had time to test pressure for the c7 clutch pack. Idle it’s only 65/70 psi. It’s is the same in 1st as it is in mode. So looks like
the tcm is functioning fine. Anyone have a good source for transmission/ transfer case parts. Allison is crazy expensive!
Fluid volume seems very good to c7 I would bet a seal has split or broken. I will do a leak down test of c7 to see what’s up

 

[MrMikey4026]

The valve module without the internal harness installed.

 

[MrMikey4026]

I think Patrick Foley has some transfer cases, I don't know if they are WTEC2 or 3.

 

[Ronmar]

probably the slower speed of 1st allowed enough torque to pass the friction material so it appeared to be working in first… did you by chance check main pressure?

 

[Xengineguy]

probably the slower speed of 1st allowed enough torque to pass the friction material so it appeared to be working in first… did you by chance check main pressure?

I didn’t check main pressure, the transmission functions really good. No shift flare ,no slipping and no codes. You are probably correct on 1st gear . I’m going to do a leak down on c7. I will check the main pressure just to be sure. I haven’t pulled the 2 filters
just the screen on the scavenging pump. As soon as I get a set of filters going to do that.

 

[coachgeo]

Anyone have a good source for transmission/ transfer case parts.

https://www.allisontransmissionpart.com/ as them for a sales location or distributor in your area. Or become one. Ted stopped selling to individuals..

 

[Xengineguy]

I didn’t check main pressure, the transmission functions really good. No shift flare ,no slipping and no codes. You are probably correct on 1st gear . I’m going to do a leak down on c7. I will check the main pressure just to be sure. I haven’t pulled the 2 filters
just the screen on the scavenging pump. As soon as I get a set of filters going to do that.

Ok main pressure is between 235 and 250 at idle. Can anyone tell me if there is supposed to be a gasket between c7
valve body and the transfer case?? Seems like there should be but I don’t have one there. Did a leak down,100% leak down.
From under the valve body?? Or valve body is venting it?? Pulled the valve body no gasket??? Will look in the TM’s

 

[Ronmar]

Was that with C7 engaged? My reason for asking was if you had something gushing i would expect to see a drop in main pressure. I am sure it is normal for all the clutches to leak to some extent and the pump makes up for that with enough volume To maintain adequate pressure. But if there was some form of restriction in the C7 feed, it would probably have trouble building pressure, and of course this wouldn't have any effect on main pressure.

Unfortunately the plumbing diagrams in 3060/3070 troubleshooting manual are not clear on the flow/source for C7 pressure. At least I haven’t found it yet.

 

[Xengineguy]

No c7 wasn’t engaged. Good thinking I will do a main test with c7 engaged. I haven’t found a breakdown with c7 valve body
to the transfer case to see if a gasket is used. I wouldn’t think they would let cast iron sit directly on aluminium ?
Another thought, with mode on the transmission shifts and acts totally normal….. I have driven it quite a bit with mode on.

 

[Ronmar]

Also which main did you check? I suspect they used the retarder control circuit(solenoid H) to control center diff lock(note in the schematic shows H and output speed sensor either going to retarder or transfer case). Main pressure is fed aft into the transfer case housing and down. There is another Main test port just above the C7 test port on the front of the transfer. The main test port up on the bottom of the control module appears to be just after the filter…

 

[Xengineguy]

I checked the main on the bottom. I will test the other when I get the truck back in the shop. later today.