The TMs warn against engine braking. The gears on the Deuce aren't really designed for that.
If you ask because you haul heavy loads downhill and the weight causes the engine to rev over the max permitted RPMs when you're in the best gear for the load and safe speed, think about installing an exhaust brake, or take less of a load downhill if that is an option.
Controlling the descent and RPMs with the regular brakes should be possible as long as you don't ride the brakes. "Riding the brakes" means keeping your foot on the pedal without releasing it every few seconds. This makes the brakes very hot and can boil your brake fluid. When that happens, the brakes fade quickly and it's time for you to ditch the truck to keep it from becoming a run-away.
The trick is to apply the brakes until your engine has slowed down enough for you to release the brakes again. You have to do this repeatedly, of course. This is not the same as "pumping the brakes". Pumping causes your air tanks to empty which could become a problem if your compressor can't keep up. I'm talking about braking hard enough to slow down the truck without locking up the wheels, then releasing the brakes to let them cool off for a few seconds, then applying them again to slow down again, releasing them to let them cool, and so on.
When the Jake brake on my Detroit Diesel quit due to an electrical malfunction on the descent from Skyline Drive in Virginia, I had to slow it down by braking, releasing, braking, releasing and so on. There are no Jake brakes for the multifuel engine in a Deuce but exhaust brakes do a great job and cost far less than a Jake would.
I had a butterfly valve brake (exhaust brake) on a Cummins several years ago. I really liked it once I had gotten used to turning it on. I didn't have an electric switch and had to turn it on with a foot activator every time I wanted to use it. That was not the ideal set up if you ask me, but that's how it had been installed. If I wanted to install one a Deuce, I'd install an electric on/off switch. That would have been helpful on that long descent on the Northern end of Skyline drive.
I hope this long explanation helps.
