I'm an OTR Driver Trainer too and I train the same way.
But this is an interesting subject. I know it is not required equipment on the truck but I was wondering if the truck is equipped does it need to be functioning. I can't seem to find anything in the DOT regulations. But think about this if you install extra external lights on your truck that are not required, why do they all have to do in working order. The next issue is that the DOT vehicle inspection requires to the driver check all safety equipment is on the truck and in proper working order, and at the top of the list is say "To included but is not limited to the following items listed." I think it could be argued an engine/exhaust retarder is a piece of safety equipment.
I don't know so I called my companies shop and safety departments. Shop said yes treat it like a blown tire and only drive the truck to the service facility. Safety didn't have an immediate answer but came back that because they feel it is a piece of safety equipment they do not want the truck driven at all. When I told them what the shop said the director of safety said he will type up a letter today and shot it over to the shop that the truck is to be repaired on the spot or towed to a facility to be repaired.
Neither the shop or safety could tell me if this was the law or just company policy.
Driven with and without jakes, doesn't matter to me. I prefer to have jakes, but you just have to be a little smarter when you don't have them.
Go down the grade a little slower, and in a lower gear. Be at your "safe speed" before you start going down, and don't ride the brakes to maintain it. When the speed goes up 5 mph, apply enough pressure to bring it back down 5 mph within about 5-6 seconds then off the brake. Repeat as necessary.
I've gone down those same grades with a Ryder rental pulling a Navy 3 axle trailer. I was loaded up with an old bulldozer and grossed right around 105,00lbs with no engine brake. JUST slow down. There's that one grade in WVA I think it's I-68 where there's a 50mph curve at the bottom of the grade. I went down at 25mph and had no problem. I continued on to Salt Lake City and had no problems. You've got to just use common sense and let NO ONE push you. I've made many trips to Salt Lake City where we had our specialized construction equipment stationed and they came from all over the states. They were used to clear bombs from old ranges. I had to rent a tractor from Ryder and you know they never have the good features you need. Check your brakes and you might even want to have a shop run the brakes for you. You shouldn't have any problems unless there's a malfunction.