We had a Jake on the first coach and have a retarder on our current coach.

This is strictly an opinion so take it for what it is worth. We would never again want a coach with a retarder. Our reasons are fairly simple. The Jake does not have an adverse affect on anything. It does not raise temperatures so using it at its full setting constantly does not require anything of the driver.

The retarder seems to have more holding power. It has a broader range of retarding power than a Jake so you can select a retarding force suited for the hill, and if the retarder is on, applying the brakes also adds retarder force to assist with braking. When using brakes heavily with the retarder on will drive the temperature up rapidly.

As Mike points out, it heats up the transmission. Heat will damage the transmission fluid and the transmission, so for those who have a coach with a retarder and a transmission temperature gauge you have to monitor the temperatures. For those with newer coaches, Prevost allows you to monitor the transmission temperatures, but you have to go through some gyrations to get at that information through the Pro-Driver. Maybe Prevost feels ignorance is bliss so they eliminated the temperature gauge on the new dash.

I have no clue what a safe transmission oil temperature is because there are no limits that I can find defined anywhere. I arbitrarily use 230 degrees just because the red line for oil on my plane is 240. If someone knows what the real limit should be please post it.

This is an observation but with all the sensors and computer power now in place it seems to me that if the temperatures get too high, the computer could reduce the retarding force until temperatures return to a normal range, but the flip side of that is that Allison and Prevost will spend a lot of time in court because any time braking or retarding force is reduced it could have dire consequences.