I just finished up my GMAX 6 Pac install last night. I cleared the taps with EFI Live then started the truck up and it wouldn't go in gear. When i put it in neutral while running the truck wont roll, but i can cut it off turn the key over one notch and put it in neutral and it will roll. When i put it in R and D, while running, i can hear a change in engine idle like its in gear but it wont go any where. What could this be?

Check and make sure the manual selecter valve in valve body is lined up in the Z slot.

Thanks Mike, I will check that out tonight.

Mike, I checked the selector valve. Its in the z slot. What could it be now?

Mike, I checked the selector valve. Its in the z slot. What could it be now?
Did you change the bell housing gaskets ? if so did the right ones get put in the right places ? any codes ?

No codes at all. Pretty sure the gaskets are right. I talked to mike on the phone and he said it sounds like it might be the c5 clutches. He said that they might be applied the whole time.

If C5 were on all the time it should give you a code for it. Also C1 and C5 gets you low gear. Since you have no gears at all I do not think that it. I would drop the valve body and take it apart. Check to make sure you got the trim valves and springs back in place properly. If the valve body is OK your going to need to drop the transmission back out again.

No codes at all. Pretty sure the gaskets are right. I talked to mike on the phone and he said it sounds like it might be the c5 clutches. He said that they might be applied the whole time.

did you check clearance on all the clutch packs during assembly ? if the C'2 were bound up it would not move ,nor pop any codes . My money is still on the gaskets :D

If C5 were on all the time it should give you a code for it. Also C1 and C5 gets you low gear. Since you have no gears at all I do not think that it. I would drop the valve body and take it apart. Check to make sure you got the trim valves and springs back in place properly. If the valve body is OK your going to need to drop the transmission back out again.

Ok I'll check it out. That might not have been what he meant about the C5s. He told me to check the C5s when I pull the trans out.

did you check clearance on all the clutch packs during assembly ? if the C'2 were bound up it would not move ,nor pop any codes . My money is still on the gaskets :D

when I put the C2s in I put the big snap ring in and checked the clearance like that and it was within tolerance. Would the gaskets being swapped cause it to not go in gear? Wouldnt it not throw a code?

If the gaskets were crossed you woud have nothing as far as movement. You would have no mainline pressure to anything. You said the truck was locked in gear till you shut it off and then it would roll. That tells me you had a clutch applied at the wrong time. Since we don't have a clean nuetral in the Alli because C5 is partialy applied, I guessed that you may have stacked the C5 clutches wrong.
I will let the local experts finish the diagnosis.

If the gaskets were crossed you woud have nothing as far as movement. You would have no mainline pressure to anything. You said the truck was locked in gear till you shut it off and then it would roll. That tells me you had a clutch applied at the wrong time. Since we don't have a clean nuetral in the Alli because C5 is partialy applied, I guessed that you may have stacked the C5 clutches wrong.
I will let the local experts finish the diagnosis.
Just trying to help Mike and throw some idea's out there for the OP to check , not trying to step on any toes . But the 1 time i crossed a gasket the truck still had movement , i could even pull it out of my shop , but there would be manifold pressure codes if that was the case.

did you put the C5 pack in upside down....?

did you put the C5 pack in upside down....?

Can't really remember how I put it in it's been a while, but I had an atsg manual and followed every step when reinstalling

Ok I'll check it out. That might not have been what he meant about the C5s. He told me to check the C5s when I pull the trans out.


Dropping the valve body may or may not be a fix but it's easier to do and make sure everything is in correct prior to all the work to remove the transmission. If you've got to pull the whole unit out I would recommend disassembling the whole thing and going over it all well, so as not to have to repeat it again. If you focus on any one thing you may miss another while your in there.