jbates346

I wanted to ask for everybody opinion because I am 50/50 with this decision. I have an '88 IROC with an LS3, T56, and now a 12bolt. I have changed the suspension to weight jacks on all 4 corner along with adjustable shocks. Since changing over the suspension the rear and been bottoming out whenever I hit bumps and sags too easy in my opinion. This car is mainly used for cruising on the weekends so I went soft with the springs, so there is currently 750lbs/in for the fronts and 150lbs/in for the rears (thats what was recommended). The rear is clearly too soft, I can only order new springs in 100lb increments. So my question is, would you guys go with 250 or 350 springs? I don't want it to be too stiff to where its uncomfortable, however it clearly needs more than what it has. I would appreciate any constructive input.

I copied and pasted the link below so you guys can see what weight jacks I got. I didn't go with the Koni's but instead went with the adjustable KYBs.

https://groundcontrolstore.com/colle...suspension-kit


Thanks!

SbFormula

I just ordered the UMI front weight jack kit a few days ago with 850lbs/in spring!!! I had been looking at the Ground Controls but did not really need 4 corners. I just need to raise the front a bit as I have clearance issues, the car is not level and the drive train u-joint angles are borderline 3*. The front springs are Eiback prokit, 714lbs/in I believe.

Search TGO, there is lots of good threads with different spring rate combos guys are using. That will give you an idea of what's out there.

I have Eiback prokit in the back and they are progressive 109/177lbs/in with Koni adjustable (1 click 20% firmer on rebound). I do bottom out on rough roads when there is a sudden dip. I have a Moser 9in and the rear is quite firm. I think lowering the car is also a factor in bottoming out.

Komet

Sounds like not enough damping to me, have you tried maxing out the firmness on the KYBs?

QwkTrip

iTrader: (22)

I'll bet your ride height is too low and the axle tube is smacking the bump stops. If you see witness marks on the axle tube then raise the ride height and car might ride a lot better. If that doesn't work good enough then get better shocks.

Ground Control sold me Eibach 180 lb/in springs a few years ago. I'd be surprised if they can't special order those if you ask. The springs are longer than what GC normally sells and maybe that's why they didn't mention it to you. I always thought the springs they sell are too short anyway and I prefer the longer springs.

UMI springs are likely interchangeable, maybe call and see what choices they have too. And of course a place like Detroit Springs can make you whatever you want.

91banditt2

iTrader: (1)

What did you set your ride height at? If your riding the bumps stops you could cut them down a bit.

McLovin1181

Any spring above 200lbs in the rear is gonna start hurt ride quality a LOT and will start killing shocks.
if you are bottoming out it's from:

1. Hitting stock bump stops that are super tall.-Solution- trim the rubber down. Making sure the tire at max compression doesn't smack anything like the fender arch or chassis
2. You are running too low of a ride height. Often times anything under 26in ground to fender is gonna run into issues.
-Solution-just raise the ride height.

-its also possible you have a large aftermarket axle that is slamming the pumpkin or torque arm into the chassis.
​​​​​
Rear spring rates?
I've run, 100, 200, 350, and 400lb rear springs and driven in cars with 500lb rear springs. trust me, don't go over 200lbs. Ideally keep the 150s.

SbFormula

Right on!!!!!
Thanks

Yep i have 27” 27.5" in back and I would not go lower. The oem bump stops are ok but the moser 9in does hit the floor. That’s actually what makes the noise feeling like bottoming out.

83 Crossfire TA

iTrader: (2)

What is it with all the vendors wanting to put super soft springs on the back of these cars? I went with coilovers and Viking shocks and they kept trying to dissuade me from going with stiff springs and I ended up going with the stiffest they would recommend, which are probably about 100# lighter than I'm guessing that I'll end up with (The person I was dealing with I've had good luck with before and he claimed to have put together hundreds of these so I figured I'll try them and they're not super expensive if they are too soft). I then asked about which shock bodies they ship with the f-body kits and after some measuring, I found that won't work either and ended up going with the next length shock and also that their brackets won't work so I'll just make custom brackets to attach them to the Moser rear to keep them in the middle of their travel.

McLovin1181

Ya, it's probably just the axle.
That's unfortunate because there's not really a fix.
9in are heavy.
You could potentially get adjustable LCA and see if you can push the axle back 1/2 or 3/4in

SbFormula

I have adjustable LCA but I like the wheels centred in wheel wells!
It fixed itself after a while. The floor is now massaged perfectly. I could grind off a bit of torque arm bracket and it would probably do the trick. But I can’t see going any lower with this 9in.

jbates346

I haven't maxed them out yet. no. From what I recall, there was 4 setting on the shock. i remember adjusting it from 2/4 to 3/4 and not really noticing that much of a difference at all. I'm thinking maybe the spring is just too weak. I mean the shock can only do so much?

Abubaca

iTrader: (3)

Keep in mind 150 is still more than stock, so I doubt that's an issue. I was lowered on GC weight jacks, rear quarter right at 26", and 150's were fine. I have the panhard relo too, so I wanted a little more spring so I picked up some 180's from GC last fall, but I've yet to do any test/tuning. Regardless, the 150's were more than enough to prevent bottoming out. Keep in mind the suspension NEEDS to articulate and move to function properly. High spring rates make your car ride like crap, right up until you come into turn 3 at 130mph, hit the brakes and dive into a turn. Then you're glad your springs can handle that kind of force. On street cruiser, definitely not necessary. -well....to each his own I guess.

jbates346

Has anyone one ran the Bilstein shocks in the rear, how were they? I am still going to do your guys' suggestion of maxing out the current shocks. But just in case ya know.

As far as the others concern, I think it was lowered down to about 26." I'm getting the car out of storage in about 2wks and I'll measure it again, but it is definitely lowered.

QwkTrip

iTrader: (22)

Don't worry about fender height, it matters not. Climb under the car and look at the gap between bump stops and axle tube.

Also measure the length of the shock rod out of the shock body. Shocks are designed to run in a certain range of extension length. Get out of that range and they don't work so good. Yours might be more compressed than what those shocks were designed to work at. You'll have to find out from KYB what is the optimal working range for those shocks. Most shocks are set up for stock ride height.