My MH has what is called a retarder. I thought it was an exhaust brake with the Cummins engine same as my PU was. It's not, more like the trans acts as the exhaust brake with aggressive downshift patterns in no throttle situations. Curious how this works going down hill compared to a real exhaust brake.
Answer: On a retarder, when you use it turns the tranny into a hydraulic pump, and restricts that flow of oil. This makes the engine work hard, trying to pump that oil. This used power, thus restricting the engine, like an exhaust brake. You can get semis with BOTH a Jake, and a retarder. Guys that run mountains with heavy loads use both.