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I am rebuilding air pressure regulators that are leaking on my bus.  I have one that is between the air manifold & transmission skinner valve.
I can't find any mention of a regulator valve in the manual in either the "air system and brake" or "transmission" sections.
There is a diagram of the modulator installation that shows the air lines going directly from the air manifold to the skinner valve. 
My question is what pressure should this regulator be set at?
The transmission is a HT-740D

Scott, you will find the info you need in your Allison service manual under modulator replacement if I remember right. be careful as I think the modulator requires  lower pressure like 75 max just from memory so check to be sure, those modulators are kind of pricey at 95 bucks or so. Allison also suggests replacing them once a year.

Hope this helps

Chris

not to hijack, but can the manual for a 740 be downloaded online?  or anyone have one in pdf they would share?

observation on modulator..I heard bubbling in trans oil pan=broken modulator-replaced all is good now and shifts better....Bob

Update
Just in case someone in the future has this question, I'm posting what I found out.
According to the local Allison service shop the air pressure shoud be 70 PSI.
I never bothered to buy the Allison service manuals, because I don't have any plans to rebuild the transmission, and I couldn'd do such a project in my current location.
I am hoping 95% of what I want to know can be found in the MCI manual.

Thanks Bob, I too heard the bubbling in the trans oil pan, and have the new modulator on order.

Thomasinnv, Allison manuals can be bought online, but I have never found any free ones to download.