In another post I chronicled how I discovered my motor mounts were shot (the fan was hitting the shroud). Since the 6.5L TD is in the back, road movements are amplified, and these mounts lasted <30K miles [actually since the problem started a year ago, <20K miles).

I replaced them with NAPA standards, but on another forum I queried members about heavy-duty mounts, and ended up here.

I doubt this is a chronic problem with the front-engine 7.4s and 5.7s, but with the loads the 7.4 deals with, maybe this link will help.

Just a comment on the urathane mounts. When we had our bus I replaced the worn out radius arm rubber bushings with the modern urathane. Big mistake! Had a much harsher ride. I would maintain that the urathane motor mounts would transmit far more engine vibrations than rubber.

I'll take the vibrations over a wandering engine.

The only thing I can add is not all urethane mounts are created equal. I have used many different urethane mounts on many different applications with varying results. In the same car one mount transferred so much vibration you would think it solid metal mounts. After some research and trial and error I found a mount that
did not transfer the vibration but held up to the heat of the engine bay. I now buy this mount a dozen at a time for my client’s cars. The only advice I can give is buy them from a source that knows it will work in your applications. The fact that is looks the same and fits is not good enough.

Neil.

The Prothane mounts get high marks on The Diesel Page, a 6.2L/6.5L forum. My AMG engine vibrates very little. I believe the sagging of the stock mounts is due to the moment arm of the overhang accentuating the road-induced motion and stressing them in ways not intended.