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hey guys, 1986 vert here.
according to the gm heritage center specs, I should be seeing 3.6inch jounce with 3.7inch rebound on each corner. my car has 75K miles, great mechanical condition overall. confirmed FJY front spring {various reports of 335 or 310lb/inch rate} w/Monroe OES Spectrum shocks, and NYR rear spring {233 lbs/inch rate} and unknown shocks. Possibly original, no lable, not leaking. suspension bushings look ok.
am only 158 lbs wet, and when I press down to obtain jounce/rebound readings I get almost nothin'. each corner may go down/back up about 1/2inch only. this doesn't match spec, am wondering if anyone has had similar results? nothing found during "search" here. suspension doesn't seem "stuck" when checked on a lift, as all wheels droop seemingly ok.
thx, bob p
Last edited by standswithabeer; May 22, 2026 at 03:40 PM.
When you jounce the car, does it come up quickly? Does it bounce before settling in and returning to a stationary position? If it comes up on the rebound and is immediately stiff with zero bounce, I would feel as though the shocks are just fine. Are you concerned about spring or shock failure?
just checked "jounce" again, by pushing quickly down on each corner. same result as posted previously, maybe 1/2inch down then back up to original height. zero bounce, just back up and then stays there.
the car handles great on smooth roads. feels planted on curves, with some very minor vert/hoz movement of the car as it transitions thereupon. it's great fun to push it a little, and only on roads I know. I would say that on other than smooth roads it feels like how I would assume a lumber wagon rides, but I wouldn't want to impune the reputation of lumber wagons.
Front sway bar measures 1.035", or 26mm
Rear sway bar measures 0.782", or 20mm
next time the car is on a lift, i'll have my mechanic nose around a bit. are they really sprung that stiff?
Last edited by standswithabeer; May 22, 2026 at 09:56 PM.
Yes they are sprung stiff, some more than yours. When I drop my 230 lbs down on the door sill of my '84 Z51, the body barely moves, it's like plopping onto a wood bench.
thx mr boomer! I understand the early c4's were very stiff, with the ride softened by GM engineers over time. what year is yours, at some point could you do a jounce tests?
If i push down on any of my C4's, the suspension depresses and rebounds to exactly where it was when I pushed it. No bouncing, just one stiff rebound back up amd that's it. My 84 and 88 are stiffer than the 93 and 95, but thats to be expected. I actually prefer the ride of the 84 better than the 93, but the 93 is much less darty on the road. The engineers did a great job improving the suspension over the years. But the 84 is still my favorite around corners.
My early production '84 with the Z51 handling option (vin ends in 3441) is the stiffest of the stiff. I can barely get it to budge if I lean on it. When I bought it I replaced the KYB shocks with proper Bilsteins, although the correct B8 shocks for the front are NLA, so I had to settle for B6 in the front and B8 for the rear. On the road it is darty on the rutted freeway lanes but ok otherwise. Corners like a go kart though. Hitting a big depression in the road and the shocks are designed to let the spring control the jounce and the shocks control the rebound. No bounce just a nice calm controlled rebound. It's pretty awesome actually. I am also running Toyo RA1 255/50 "autocross" tires so I can keep using the original 16x8.5" front and 16x9.5" rear wheels.
1986 vert jounce / rebound test fail
