The engine is not under load in neutral. I get a hint of it, so no escaping it there.

• Neutral @1800 RPM - subtle, but there... half the time.
• Cruising @1800 RPM - Annoyingly there (about 15 min up to 1 hour), then subtle, then annoying.
• Accelerating - unsure, this never lasts long enough to sort out.
• Decelerating @1800 RPM - the one clear and obvious symptom, even when the FIPW shuts the fuel off.
• 2nd gear @1800 RPM - shaking, but without the TC locked... so it's subtler.
• 3rd gear @1800 RPM no TCLU - softer shake than second gear.
• 3rd gear @1800 RPM with TCLU - this one's the strongest, particularly in decel.

The best part - it's fickle. Stinky refused to drop his underwear during the last two visits to troubleshooters. I can drive to work without so much as a shimmy, and Stinky sounds so slick. Then... the drive home from work is totally Chitty Chitty Bang Bang. The next day, the reverse is true - Chitty morning and slick afternoon. It's maddening.

 

With the TCLU, there is a solid connection from the front of the motor to the rear wheels. FiznUKa mentioned above about removing the fan belt and trying it. That would eliminate all the rotating items on the front of the motor.

 

Make sure you aren't missing a chunk from a fan blade next time you're under the hood.

 

I spotted that and that's one test I can do after I've eliminated some other stuff (no water pump or alternator when I try it). I'd like to thank FiznUKa for the idea, and you for reminding me... because my head is full of stuff that makes me forget things.



I thought I already looked, but I'll double-check it.

 

Remove the rear drive shaft (witness mark it first) and drive it for a day on only the front drive shaft and drive line? (It will handle weirdly, so beware).

 

Just spitballing here but...


Back when you were chasing jumping jekters and engine noise, etc... did you ever do a compression test?

 

365 to 380 PSI dead cold... but that was then, things could have changed. What disturbs me is the coming and going of the symptoms. I don't fathom how the engine shakes one time, but not the next (the harmonic balancer is my only hope for sanity at this time) - with no link to engine/transmission/outside temperatures. I think I know the answer, but can compression loss bring that? Will U-joints come and go?


I ask this like it's all just one problem, but I can't yet rule out the possibility of more than one problem leapfrogging over each other.

 

If you can feel it sitting still and reviving the motor up, leads me to think it in the front of the motor. Perhaps a loose fan, a loose fan clutch, the power steering pump, or the A/C. Engine RPM's have more to do with the vibration rather than driveshaft does. I guess even the alternator could cause it.

It took me a year to figure out the vibration in my 08 work truck. Mine was self induced. I installed a set of centramatic wheel balancers and the ones on the front actually made the truck vibrate. And the whole time I thought it was in the rear of the truck.