So I had my 71 240 out for a little drive today. I have an early 5 speed. It makes an awful grinding sound while decelerating unless I disengage the clutch. I check the oil, and it was a little low, but not terrible. I'm planing on changing it out for some synthetic. Any thoughts as to what could be causing this sound.

Thanks,

my 81 zx was makin that same noise and i did just what you said with the synthetic and the noise was gone.

sounds like a bearing. my 5 speed (79) is doing the same thing. gonna try the synthetic, but if that doesn't do the trick, i'm going with a rebuild kit that includes all of the bearings and just replacing them all, like here:

http://www.drivetrain.com/nissian4_5sprwd.html

Nice, that gives me a little optimisim for when I get that done early this week. Hopefully its not bearings, but that wouldnt be too big of a deal to do.

You can pull the drain plug, there is a magnet attached to it. If there are metal pieces attached then you know you've got bad internals.

Your clutch disk could be worn allowing the rivets (on the disk) to rub on the flywheel when the two surfaces are in contact.

My .02

Your clutch disk could be worn allowing the rivets (on the disk) to rub on the flywheel when the two surfaces are in contact.

Would this cause the sound only on deceleration? It seems to me like that sound would always be present (when the clutch is engaged)

Thanks, for the ideas, and keep them coming please. I might get a chance to change the oil tomorrow, I'll post how it works out.

Ok, Its been a while but I have a quick update to the situation. The noise only occurs in 1st and 2nd. I drained the oil and there were a bunch of filing (i wasnt too worried about that) and a piece of metal (alluminum I think) about a centimeter long. So im guessing I have a bearing gone. I guess I'll find out for sure once I pull it out and take a look at the internals.