Well, the Red devil is running again. It STILL has a pulsing vibration you feel through the seat. Only at 1000-1400 rpms in neutral. Driving down the road at the same RPM or even power-braking it in gear to the same rpm range there is no vibration at all. The truck has done this ever since I've had it. For various other reasons ever single rotating assembly piece has been replaced. The only part original to the truck is the flexplate. I used a donor shortblock from an exploder that had an Aode-w, and assumed the flexplate from that wouldn't fit the E4OD converter. The converter and trans are new to the truck junkyard units. Harmonic balancer is new. I started it this morning with no belt on it, and it still vibrated. The motor mounts are new, the only thing I can think of left is the transmission mount or the exhaust transmitting the vibration to the cab. From what I can see, neither touches anywhere. The exhaust is just a temp one I cobbled together with old junk for now. The trans mount looked 100% fine when I swapped the tranmission, but IMHO that's the only thing I can think of that could be it?

Thoughts?

edit - also, I really don't think it's the old flexplate, from what I've seen when stuff like that is bad, the vibration gets worse with more RPM, also putting it in gear shouldn't affect it.

 

Does it still vibrate when it's just idling, not moving?

 

Yep, only in Park and Neutral. If I put it in gear and foot brake it up to that rpm range there is no vibration. Which leads me to believe it's a mount of some sort. Or maybe the front crossmember or motor mount perches have loosened up. I am missing the center support mount on my cobbled up temporary exhaust, but IIRC the vibration was there with the stock exhaust also.

 

Alright well from what I'm gathering, it could be the motor mounts as you mentioned, or possibly the tranny mount. Maybe try securing your exhaust with some wire or something and see if it still vibrates.