i just installed urethane rear spring isolators on my 86 gt vert with FMRP "c" springs. now the backend sits 3/4 -1 inch higher. did i miss something on the installation? it should only have raised it maybe 1/4 - 3/8 of an inch.
make sure the ends of the springs are pointed I think to the driver side of the car. I did this early spring and had them 180 out and it jacked up the car alot.
Like Wildstang90 said. It's likely that the springs are not seated correctly.
On a vert, even with new poly isolators, with FRPP C springs, you should have 3/4+" or more drop from the factory spec'd height.
If the old isolators were worn, that could drop the rear by ~1/4"->1/3+" from the car's factory new height. I'm not sure what the factory spec height is for a vert. But, it's at least 27" at the fenders. It may be 27-1/2" or more.
FWIW: I don't like the FRPP C springs. I like them even less on a heavy *ss vert. If you're doing the drop just for looks, that's fine.
Hoeever, if you're looking for better handling, the FRPP C annd B springs are a joke. The drop is too great, and many suspension parameters get screwed up when the Fox/sn95 are dropped more than ~1" from the GT hieght. For a vert, for handling, I'd suggest at most, the Bullitt or Mach1 springs with poly isolators. Or, Mach1 springs with rubber isolators.
C springs are meh. The rake is good and it handles okay on perfectly smooth roads, but it rides like a brick and you better pray if you ever hit a bump in a hard turn.
I'll be replacing mine at some point with a better spring setup matched to my tokicos
It depends if a person wants handling or looks. The GT springs are stiff as they are. For handling, you can not lower the car at all, unless you increase the spring rate. The stock GT height is boarder-line too low as it is for the spring rate.
For pure handling, people don't want a drop of more than ~3/4" and rate of at least 750. Of course, I'm talking about a non-modified k-frame, FCA, etc.
The struts and shocks make a massive difference. People can't just go to a stiffer spring rate and hope that some POS KYB or Monroe struts or shocks do anything.
I had the fixed-rate Toks before - much better than stock! I now have adj Toks to better match my Mach1 springs. Still, dual adjustable Koni or Bilsteins are much better (also cost much more!) than my adj Toks.
A Ford Fusion or an S197 have much better handling and tons more comfort. Of course, it's a suspension design from scratch that's over 20 years newer.