knocking in neutral and park
 

2002 D2 with 4.6 installed. Approx 40,000 k's on engine.

Truck is running fine and everything seems to be smooth. Shifts well, no clunk when shifting in T'case or transmission BUT:

After the car warms up I get a knocking sound coming from somewhere. I've kinda narrowed it down to transmission because you only hear it when in park or neutral. nothing while in drive or reverse. to me this would rule out engine since shifting gears shouldn't have any effect of sounds in the block.
Also I've ruled out exhaust and cats for the same reason. Exhaust wouldn't care if I was in drive or park...it would always rattle. Out maybe i'm wrong?

Also as I said it only starts after truck is warm. Upon start up it does not happen.

Any ideas before I have the tranny flushed and fluid replaced?

Maybe it's just an LR sound and if thats the case i'm fine leaving it but my last D2 I had for 7 years and never had this type of thing happen.

Thanks for any help.

Sometimes the flex plates crack and make noise like that.
I don't know if flushing the transmission is a good idea. Sometimes it does more harm than good, depending on the condition of the internal parts of the transmission.
You might be better off just doing a simple drain and fill.

Agreed. how would you suggest I check the flex plates?
Probably a stupid question but is it ok to drive if I have a cracked flex plate?

Well, it's not going to kill you. It could leave you stranded if it breaks apart. Of course it may not be the problem too.
You could try searching around and see if there is a way to check it without taking the transmission out. I know I've seen that problem posted on this forum, with pictures. But, I haven't seen the problem in person on a Rover.

Remove plug and rotate engine to access each of the four bolts.

Often the plate is just loose, not yet cracked the bolts require re-torquing.

......

It could be that the engine is totally unloaded in neutral or park whereas it is partially loaded when in drive or reverse even if stationary. Can you post an audio or an audio/video? this will help ID the problem if one exists.

IMO it is not the flywheel flexplate otherwise it would be noticeable in gear and not in neutral or park.

It could just be loose. It does it when it's warmed up and not in gear. So when it's cold, the fluid is much thicker. Then when it warms up, the fluid thins out and takes most of the load off of it. Then of course it would be loaded up when in gear.
It's at least worth checking out. Hopefully it's not something internal in the torque converter.

OK just to close this one out, It was in fact my flex plate.
deep clunk sound in neutral and park. Went away when you gave it some gas. Basically anything over 1500 RPM.
Bought the part form AB for $60.00. Installed and now the truck runs great. Had a home-garage LR guy install for me. Took about 8hr. My old flex plate was cracked all to hell in the centre.

I drove the truck for about 2 months before fixing. Everyones results will be different but I would say if you start hearing the sounds, it's ok to drive but starting figuring out a fix. After 2 months I figured my luck would run out any second.

Great thread. Appreciate the follow up. Did you happen to come across any write-ups for the replacement while you were browsing the net? Did you pay attention to the repair and can you list the steps involved?

I did not do the replacement myself. I found an LR garage mechanic not far from my house and sourced my own parts.