I had 3/16 inch UMHW (polyethylene) spacers cut to even out my sedan suspension after adding (03) Z springs [I got approx. 3/4 inch drop in front and 7/8in the rear]. But when I placed the spacer between spring and rubber upper seat, it pulled the spring away from the rubber seat, creating some spring movement (slop). Maybe others are somehow building an inner lip like the Energy 3/8" spacers keep the spring tight against the upper seat? to I thought a better option to use my flat spacer might be to put the spacer between the upper seat and the body itself (see photo - nevermind, the file size was too big to be attached ). It seems to work well, but I wouldn't go more than 3/16 on the spacer since the upper seat will be displaced too far from its mounting clips. Let me know if you are interested in a pair of these 3/16 spacers, they included an extra pair since they had to charge me for a template fee. I'd have to charge $20 shipped - I paid $46 for two pair including the template fee.
I can email the spacer photo if you are interested. The drop is nice and even (still a bit of the stock extra fender gap in front but fine for me). I'll post photos of my car when its not completely filthy, hopefully at the track in a few weeks.

 

i read your post 3 times but i still can't picture what you're saying...

 

Yeah, how about resizing your picture and attaching it. And how about a crude diagram drawn in MS Paint. I think I beleve what you are trying to do. BTW are you using the spacers in the front? Back? Both?

 

Sorry, I'll work on the photo.

 

The white spacer is visible above the upper seat (conical rubber thing). Hopefully you can visualize that if the flat spacer was placed between the spring and upper seat, it would pull the spring away from the inside portion of the conical seat. This allows the spring to float from side to side, depending on the thickness of the spacer.

 

Okay I see what you did. Yeah, you could use the Energy Suspension 3/8" isolator as well. Good job making your own. Did you do any spacers for the front?

 

that makes sense. thanks for posting a pict.

 

No spacers for the front since I just wanted to raise the rear a bit to level it with the front. Typically 350z springs lower the sedan rear 1/8" more than the front.