260Z rear suspension

[highway star]

Hi i need some advice regarding my 260Z rear suspension. There's been a knocking sound coming from the rear when driving over bumpy roads since my car returned to use about 4 years ago (it was off the road for years). It's been on a ramp and rocked up and down and you can hear the noise. A few years ago i attempted to lower the car slightly and bought some lowering springs and new shock absorbers but there was a problem with the springs and it didn't work out (early '74 stuff). So now i'm attempting to lower the car again (for the third time) and fix the knocking. I've taken one side off today and so i can get the right stuff can anyone answer-
1. whenever i look at parts i see 'up to 8/74' and 'after 9/74'. does this refer to manufacture date or registration date? My car was registered 10/09/74, chassis no 691.
2. do i have the correct top mounts for the 260Z ?
3. on the strut casing is the numbers 55302 the either 3500 or 8500 and underneath that it says 3 y 3 0. can anyone tell me if this is correct for my car?

 

[Mr.F]

Parts recommendations are by date of vehicle manufacture. The strut tops are correct for 240Z and early 260Z.
55302- is RH rear strut. You should find different codes on each strut.
N35** in the latter part of the number would relate to early 260Z...

 

[highway star]

Thanks Mike. I thought all 260's used the more substantial mount and i had the wrong ones fitted and that's what was causing the noise.
next thing is the springs. are these standard springs? I bought some second hand ones as well but can't remember which ones eventually went on.
I need to know if have the correct struts as it could be a bodge by a previous owner. so those numbers relate to 260z?
sorry for the questions!
I may be giving you a call Mike for some springs but want to make sure first

 

[highway star]

spring

 

[jonbills]

I wouldn't think the spring would cause a knocking noise.
More likely to be one of the bushes.
The bolts that clamp the inner control arm bushes can be hard to do up tight enough - they knocked on mine until I bought a proper 24 mm ring spanner.
I think the strut insert could also knock if its one that needs a spacer in the strut tube.

 

[moggy240]

I had a knocking at the rear and it was a loose big strut nut that holds the shocker in the tube

 

[highway star]

well most of the bushes were replaced but the ones on the moustache bar weren't and they do look past their best so perhaps they could be the cause?, any thoughts?. also i remember struggling with those inner control arm bolts too. i'm gonna re-check everything.