In the rear suspension, the spring is crushed into a black, cone-shaped, rubber/plastic component called the "Top Seat". (See pic below.)

The bottom, flat-side of the top-seat has a cut-out pattern to it. Does the top seat "fit" into the tower/frame of the car in a particular orientation? And is it possible that when the top-seat isn't properly fit into its groves, the one rear corner of the car could be higher than the other...?

...because that's where I am at the moment. I had bushings customized to fit flush against the shelf of the top-seat, and installed in order to raise up the typical droopy rear for the RWD Sedan and some aftermarket springs. After settling for a week, the driver's side is simply perfect, IMO; I'm very happy with it. But the passenger side is way too high in comparison to the driver's side. Almost a half-inch too high. And now I'm trying to figure out why.

My mechanic did the install, and I was there. I recall a very distinct difference in the effort involved in re-seating the rear suspension. The driver's side bolted right back up, but the passenger side required a lot of muscle in order to get things reattached. A week or two later, looking at the added height on the passenger side, I'm starting to put 2+2 together, and came up with this theory, but can't find any pics of the frame-side of the top-seat, so I'm just guessing here.

Anyone with experience installing springs... be great to hear some advice on the matter.

 

AFAIK the upper seat mount is flat without any way for the upper cone seat to be higher. The lower spring seat has a recess for the spring to fit down in to, it's possible that the lower seat isn't situated properly w/ the spring sitting on top of that recessed valley.

 

Pretty much what blnewt said.

 

I was trying to eyeball the upper seat today, and it looks like the mount area is ridged to fit, but only a little. Not at all what would be causing this fitment issue.

Lower seat then... that makes sense. Thanks, Brad.

 

Hopefully that's the culprit, seems like the only thing that could be amiss, and if it is sitting on top of the cushion rather than down in that recess it could account for about a 1/2" difference.

 

If I jack the car and pull the wheel, can I get in there enough to see if it's seated improperly, to confirm things?

And yes, that's really all it is: a 1/2" problem. Driver's side is really nice, Brad. I've been wanting to take pics, but honestly it's taken me a while to realize the problem, what with waiting for things to settle and all. And it just never occurred to me that one side could be different than the other, until my friend and I were eyeballing it this weekend.

Quite a shock.

 

Maybe up on rear jack stands then use a mirror to see down in the bucket Not sure if removing just the rear tire would give you a shot in there w/ the rotor in the way.
Here's a pic of the bucket and you'll see that big indent for the end of the spring to rest in, the rubber cushion is molded to fit in there like a glove, so if it's off or the spring isn't rotated properly to coincide w/ that pocket you'll be off.

 

If you pull the wheel, everything is right there for analysis. The lower seat is aligned properly, and the end of the coil is right where it should be... confirmed by eyeballing it and feeling of the indentation under the bucket as it compared to the end of the spring itself. In other words, the spring is right where it needs to be, and so is the lower seat.

What the heck?

I need to take a much more studied approach to this problem. With floor to fender measurements in more than one location, with the car turned around in each. If I can't get this figured out, I may very well be paying my mechanic to remove these bushings, and go right back to square one.

 

Wondering if swapping the springs left to right & vise versa would result differently. All the parts should be 100% identical so try diff combo.

 

This is a repost of the same comments on G35Driver. I've been looking for advice in both forums.

------------------

This was interesting. Before installing these 5/8" bushings, I very clearly had a droopy bum. At least a half inch lower than the front. You'll have to take that at face value... otherwise, why go through all this effort, right?

Anyway, after installing the 5/8" bushings, it just didn't look right. I waited a couple of weeks for things to "settle", and stated looking at the problem more seriously. At first, I thought it was just one rear corner. But with some help here and on myG37.com, I came to thinking it was both rear corners.

So I took a bunch of measurements. Found three very level locations, and took floor to fender measurements (in inches). At each location, I flipped the car around and did it over again. Then I calculated an average measurement for each location, and a final average of all three.

The result: my rear end is actually *HIGHER* than the front now, by an average 0.6".

So in review: my rear was (approximately) 1/2" or more lower than the front before the bushings, and now it's 1/2" or more higher than the front, after the bushings. Essentially, adding the 5/8" bushings increased the height well over an inch. That's messed up.

Why did this happen? I'm assuming because the polyurethane has almost zero give to the material, whereas the upperseat is made of a softer rubber, and absorbs the shape of the spring better.

Anybody have any thoughts? Here are my measurements:

 

Wish I had any help here, something strange sure seems to have happened along the way, but what??

 

I'm going to try this again with 3/8" bushings. However, there's not enough poly material at the inner edge of the 3/8" bushing to support beveling the edge like I did with the 5/8" bushing... so, instead of grinding the bushing to a 45* angle to match the upper seat, grind the upper seat to a 90* angle to match the bushing.



This approach is actually much easier, assuming you have a grinding wheel, or a Dremel Tool.