Eaton 8ll when cold and moving range selector air leaks and have no gears

[MaxtinDel]

I have a 1996 Mack cl713 tri axle dump. It has a eaton 8ll 8 speed transimission. When it’s cold out when I start the truck every morning I have to flip range selector into high to see if it’s gonna work for the day. Once I do that air pisses out of the transmission somewhere I can’t physically see it until I head a loud clunk and then truck is good for the day. It only happens in cold weather and in the summer when truck is parked Friday afternoon and starting it up Monday morning. 
 

so far I have replaced the shift knob 

gaskets and valve in air selector valve 

and filter in back of transmission.

 

any ideas would be appreciated 

[doubleclutchinweasel]

My RT-915 had the same problem.  I usually had to flip it lo-hi several times before it would work the first time.  After that, it was fine for the rest of the day.

I think mine ended up being a combination of an air compressor bypassing a little oil and the "slave valve" on the transmission.  Of course, the old model had been discontinued, and I had to adapt the newer model to it.

Looked something like this.

[steeler]

First step is to try to identify where the air leak is coming from. 

If it's leaking into the case of the transmission, the air will be heard at the breather which is on top front left in the shift bar housing. 

When you say you replaced the valve, I'm assuming you mean the slave valve on the driver's side of the transmission? 

If so, and you've replaced the shifter knob, then the only thing left is going to be the o rings on the range piston. Not a big deal if you have some mechanical ability, you can remove the range cylinder and replace the o rings without removing anything else. 

[DieselDog5.9]

Take the line off the range cylinder and put some air tool oil to it.  This may help an old dried out O-ring.