How do you use the jake brake on a truck with an automatic transmission?

My truck is a 2020 Freightliner Cascadia with a DD15 engine and a DT12 transmission. Don't you think that when freightliner made the tachometer, that Freightliner would have made the redline on the tachometer to represent the actual danger point of RPM's on a truck with a DD15 engine and a DT12 transmission?

 

I don't own the truck.

 

I'm not saying that you are wrong. I was just asking questions, trying to learn.

 

singlescrewshaker wrote the following: "Most cases jakes gonna be most effective between 1800-2200rpm. Let her spin.!

Also, these new autos are synced up with the engine. I'd bet it won't downshift to an unsafe rpm.."

otterinthewater, you wrote that "if you saw 2200 RPM's on your tach, you would have a #### heart attack." singlescrewshaker is saying that the jakes are most effective in a range that includes 2200 RPM's, and he says that he bets that the transmission won't downshift to an unsafe RPM, even though i said my truck downshifted to 2200. If singlescrewshaker knows that my truck downshifted to 2200, and if singlescrewshaker says that he doubts that the transmission would downshift to an unsafe RPM, then it follows from that that singlescrewshaker don't think that 2200 RPM is too high. Yet you say you would have a #### heart attack if your tach was at 2200. I am surprised you don't see a contradiction there.