allison ht740 question

any ideas on this?
96 mack intermittent tran problem.
wont go into reverse unless i shut off the truck, toggle the shifter, start the truck.
it goes into reverse, but only one time.
when it does go into reverse , after about 10 seconds the truck dies.
is there a lockup solenoid somewhere?
also cut open the filters everything looks clean.
thanks . this is driving me nuts.

 

thanks for your reply.
yes it dies after about 10 seconds. never tried it without the brake on , i am afraid i wont get it back in the shop.
no pto. my pto is driven by the engine. its a front load refuse truck.

 

thanks.
i will take a peek for those hoses.
would it be possible its located inside the truck. i was told there is a elec/air solenoid valve located under the center dash.
i took a look and it looks like a MAC valve. 3 air lines and 2 wires. 12vdc 6 watts. but dont know if it is the lockup or not?

 

thanks.
this is what i found under the center dash panel.
it looks like the pic although the numbers are different.
mack dealer sent me the parts list and trans diagram.
item 12 in the circle C area on the last page shows the solenoid, but does not says what its purpose is.