Air pressure leak

You've got to determine if there is a leak or just a gland hand gasket or something simple. I'd do an air test first. Run the the truck up to full air then shut it down release the brakes and apply 90 pounds of air. It can not leak more than 3 PSI for a minute for a semi. Next you need to walk around to see if you can hear it leaking. You just release the trailer brakes then the tractor brakes. Be sure the either the brakes on the tractor are set or the trailer NEVER both at the same time. I drove truck and trailer and I believe they are much more easier to find an air leak. If you have a trailer brake or trolly brake you can pull that down and if it stays down you can do a walk around again.

 

What did the problem/solution end up being? I'm having the same issue. 2017 Freightliner, low transmission air each time I start her up + losing brake pressure faster than usual. Heading to a shop shortly, I'd like to have an idea of what's going on before I get there.

 

Why would you put the truck in D?

 

What was it?