Tranny problem? or something else?

stock 2000 XJ 2,5 Turbo diesel with manual tranny NV3550.

When idling and clutch released it makes clunking/popping metallic noise (as if gear is hitting an edge or two gears with incorrect tooth pattern are hitting each other)

When clutch depressed = silence.
When under load (eg. normal driving and gear in) = silence

The noise is there ONLY when idling without load.

New clutch and pressure plate, new clutch throwout bearing, new pilot bearing, new flywheel, new axial bearing...
All tranny bearings new, also tested with another tranny....both of them have the same issue.
But when tested on a workbench (tranny driven by el. motor), both of them run absolutely smooth and soft without any disturbing noise.


There are absolutely no marks or traces of damage anywhere, no debris...everything bright and shiny. Tranny fluid is correct, new and clean. Shifting is easy and smooth, clutch operation detto.



ONLY THAT STUPID NOISE.

pls anybody an idea?

My first guess would be throwout bearing, but they sound like running water, and you have a new one, anyway. What I may suggest is a pressure plate or clutch disc that's rattling. I drove a few trucks with the Cummins 4BT engine. I know that at 3.9 liters for a four cylinder, it's gonna be rough. At idle, tranny in neutral, foot off clutch, the clutch assembly would rattle. Slight pressure on clutch pedal, or slightly raise idle, and the rattling would subside. A four cylinder engine just does not have enough firing pulses per revolution, and especially in a diesel, the crank starts to slow as it comes to a combustion cycle, then afterward, speeds up. Not a very fluid motion. Often this 'cogging' can cause things like the damper springs in a clutch plate rattle.
I'm not real familiar with your set-up, but I'm throwing some ideas at you, maybe some places to look!

Uh. After googling and searching i have found the "neutral rattle" is a common issue with that tranny.

http://groups.google.com/...tj&btnG=Search&sitesearch=

http://forums.jpmagazine....nv-3550-rattle/index.html

http://www.jeepforum.com/...utral-1059503/index2.html

What wonders me is , that it is not from the beginning but it started after replacing the clutch and throwout bearing. But i might be wrong and it was there before but hidden behind the noise from a faulty throwout bearing.

The other thing is that i have another car with the same setup (2,5TD, NV3550), but 4,5 inch lift, NV242 transfercase (instead of 231), disced, locked, regeared (and heavily off-road abused) and the tranny is quiet.