I-shift issue

Sorry if there is an answer to this question but I have read and looked and haven't found it.

I have what appears to be an internal leak..I lose pressure in primary and secondary in about an hour being parked down to aout 40 psi. Then low air to trans. comes on. When driving, the compressor cycles exactly at 9 minutes when driving on interstate with no traffic.

I checked everywhere and changed out alot of fittings., pass though valve, psi protection, check valves, etc..abs relays good.

But the leak is very audible coming from a hole under the transmission bellhousing? Right after the engine oil pan where the trans starts. I can place my hand over the hole and the "Sssssssss" goes low, then when I remove my hand its loud again.

Anyone know what could be leaking in there? I think the trans would have to be dropped.
I am taking it to the dealer in the morning but wanted to give it the ol college try before I go.

Thanks

 

Thanks Benrab.

It never dawned on me that a transmission air leak can drain the truck of air.

I will post the results and cost as info for anyone else that may come across this situation.

 

Thanks.
I just got from a dealer and they have a 2 week waiting for any heavy work. Ridiculous since I called last night and they said 2 days. So I took the truck back home.
Question: is this a condition that gets progressively worse, or does it just leak the way it is? I ask because I want to take the truck out of state or to a different area that's not southern CA. Here everyone is booked it seems.

Thanks again

 

Also: I noticed on a youtube video that there is a countershaft brake which has an air line going to it. Could this also be the trouble?

 

Thanks again Nasriza. I got nervous thinking about it, so I drove it to TEC in Fontana. It was starting to grind a little on the low gears, so yeah, I think you are right. I probably would have needed a tow if I took out a load again.

What sucks is my warranty expired 7 days ago. I will post results.