HELP Eaton fuller 8LL/9LL transmissions

Eaton fuller 9LL or 8LL problem. I bought my truck 2 or 3 months ago and everything was working as it should. All of a sudden I get into my truck one day and the deep reduction stopped working. As of right now I can flip the switch foward and you can hear air being supplied down to the transmission, but it does not make that final locking noise and does not engage. I do not use the deep reduction a lot, and when I do it’s always from a stop “sitting still” and usually just for Low gear. Any help would be greatly appreciated!

Thanks

 

I didn’t realize their was all that in the deep reduction valve! Makes since tho, thanks for the info I will check into it tomorrow!