I've been refurbishing my 240Z rear suspension recently and when ticking new parts off the microfiche I came across item no. 55418 N3000 on section no. 92-10. Described as a plate to the diff mounting member. Haven't noticed one of these on any cars before but there are two holes there to bolt it on. Were they always factory fitted ? Anyone got a picture and one to sell ? Thanks, Dave

Good question!!! You have me curious now. I'm sure one of the history gurus like enlighten us.

Tom

Is this what you are talking about? If so, it definitely was not always fitted, none of my cars have it.

http://classiczcars.com/forums/showthread.php?t=25827&highlight=plates+differential

Unless you can find one locally in a junk yard or can live without it, you're better off cutting up some 1/4 plate and stacking it to the height/weight you want. I actually have a spare one and would be happy to part with it, but it's approx 3 lbs. US of solid steel. I'm unsure what it would cost to ship to you from here. Here's a pic. I'll take measurements tomorrow in case you want to mfg your own.

Wasn't this added to help eleviate vibration problems or I'm I thinking of another part?

I believe so. After looking at the two parts I have, one is a solid steel slug, and the other is two plates welded together. They're both the same size and relative weight (2.5-3.0 lbs) as far as I can tell. The solid one is the original part from my original 73, and the other came off a 73 in a JY that somone had done an R200 swap on, which included a 280Z diff member so I can't say for sure what year the latter came from, or if it was fabricated.

My '73 did not have this piece but a '71 parts car that had it's engine, tranny and diff already swapped out did. I have no idea what year 280Z/280ZX the parts come from though.

My '73 had one . I left it off when I reassembled the car. I couldn't see what the function was . Latter I read that it was as previously stated, to help with vibration. I don't feel any vibration so I still have not installed it. That is over 10,000 miles back Gary

It's a simple mass damper used to reduce driveline vibrations. Almost every new car has them somewhere. They are common on exhaust systems, differentials, and frame rails on pickups. By adding mass to a component, the vibration frequency is changed and certain error states are moved or eliminated. An exhaust, for example, might have a vibration at 3000 RPM - right at cruising speed. By adding weight, the RPM could be raised to 4000 RPM which is only briefly seen.

The new NISMO 350Z uses them in the body and Nissan has been advertising them as a performance feature. In reality, all mass dampers are band-aids to cover up a noise or vibration issue.