So I have a question. What makes a spring more bouncy? A soft or firmer spring?

I'm wondering because I have a bounce. it feels like in the front of the car. Not sure if it's the front or rear springs...or perhaps a transfer of the weight from fronts to rears is causing the bounce. My setup: 1986 GT Fastback

197 lbs Moog #6556 (FRONT)
275 lbs AFCO Coilover Springs #22275CR (REAR)

Just wondering if I were to get stiffer rear springs if this would improve the ride?

What makes you believe your springs are the source of this "bounce"? I'd suspect blown shocks and/or struts first.

Give us a full run down of the suspension on your car. Stock or lowered, poly or rubber bushing, which shocks/struts, springs, wheels, tires, etc...

Right. Right. Sorry. my bad.

Because I replaced the Front shocks (Monroe Sensa-Trac) when I installed the new front Mogg springs to raise the car for my new 18" rims. That's when I noticed the bounce.

Previously I was running the same rear setup (Custom AFCO coilovers on KYB's) but with the lower OEM ARC 88 12" Front springs on my 1986. With the ARC's at first I had KYB shocks but they seemed to stiff, hitting California pot holes and what not, so I swapped them out for softer Monroes. Which felt more comfortable and seem to handle the potholes better at that time.

So I'm wondering if I have a bad spring combo, (197lbs Monroe's to 275lbs KYB's) or if its shocks and struts.

One note: I personally felt that one of the monroe shocks wasn't quite as "good" as the other one when I ordered the pair. I could hear gas squirting inside when I would compression test the unit. I was told years ago the hand test was not accurate anyway and to ignore it. Also it seemed the "NEW" shocks were not better than the old parts. But they were new so I put them in.

I would go corner to corner and jounce the car to see how many ups/downs it take to stop.

Typically a bouncy ride is from the springs having too high of a spring rate for the shocks/struts to properly dampen, but your spring rates are quite mild. Another cause is if you are riding on the bump stops (effectively a high spring rate), but your car should be close to stock height. Another cause is bad shocks/struts, even if new, they have likely been sitting on the shelf a long time and could still be bad.

Well I don't have hardly any up/downs from the bump test.
The front of the car (when hopping my body on it) seems stiff. And the rear has some down, but not any up.

I'm wondering it I can add stiffer rear springs. I'm thinking the stiff bouncing is the weight traveling from a firm front to a less firm rear end.

The Front 197 to Rear 275 isn't much difference considering the weight of the stock 2.8
What about upgrading the rears to 300 or 350 lbs springs?

[This message has been edited by SP1200 (edited 03-12-2018).]

Something isn't right in the front.

The front springs have a motion ratio of about .5 (they are placed about 1/2 the way between the lower a-arm bushing and ball joint). With a 200 lb/in spring, the effective spring rate at the wheel is about 50 lb/in. So if you sit on a front fender, the suspension should go down. If it doesn't, something is binding, you are sitting on the bump stops, or the spring rate is much, much higher than 200 lb/in.

In the rear the motion ratio is about .97, so your 275 spring rate, becomes about 258 lbs/in effective spring rate at the rear wheel.

Sorry. I checked again. Nothing is binding. I used a tape measure and jumped on the front.
I got it to drop anywhere from half inch to almost in inch.

The rear I could not measure as Im alone, but it drops quite a bit.

If the corner with a 50 lb/in spring rate at the wheel moves the same or less than the corner with the 250 lb/in spring rate at the wheel... something is wrong.

All sides seem to move about the same. I'll get a buddy over to measure with a tape when I jump on. I'm 220lbs is that enough?

Does the height adjustment of the castle nut on the coil-over sleeves make any difference?
Does the aluminium sleeve flex at all?

quote Originally posted by SP1200: Nothing is binding. I used a tape measure and jumped on the front. I got it to drop anywhere from half inch to almost in inch.

quote Originally posted by SP1200: I'll get a buddy over to measure with a tape when I jump on. I'm 220lbs is that enough?

I think someone of your weight should have little trouble getting the front suspension to travel more than "half inch to almost in inch".

Turn your front wheels off to either direction and have a look at your front bump stops. There should be plenty of room between them and the lower control arms. Pictured below is an old photo of my '84 with cut springs before I shortened the metal cones of the front bump stops. Notice how the rubber bumper of the bump stop is actually sitting on the pad of the lower control arm. Your suspension with the new replacement stock height springs should not have this issue... but double-check and let us know.

Bump stops were trimmed years ago. There is plenty of clearance.

This may seem counter-intuitive, but the front suspension needs firmer springs than the rear. Due to the suspension design, the front springs have much less leverage than the rear springs. As a general rule of thumb, the front spring rate should be about 1.5x the rear spring rate. You can see this in the stock spring rates, where the front is around 200-220 lb/in and the rear is around 140-150 lb/in.

Because your rear suspension is significantly stiffer, the front is going to feel like it's bouncing around. That's because the front end moves around more, while the rear end is firmly planted. You can correct that by either firming up the front suspension, or softening up the rear.

Oh, and here's a little story: I experienced a similar phenomenon during my latest suspension upgrade. In a previous upgrade (back in 2004), I had installed KYB dampers and Eibach springs all around, with urethane bushings. My new suspension was installed in 2 stages. The first stage was the rear suspension: 350 lb/in coilover springs, Koni struts, '88 rear cradle, and rod-end suspension links. So for a short while, the rear suspension was significantly firmer than the front. It made the front end feel bouncy. The sensation was almost as if the front shocks were bad. When I installed the new front suspension (Koni shocks, 500 lb/in springs, and tubular control arms with rod-ends), the bounciness in the front end went away.

[This message has been edited by Blacktree (edited 03-14-2018).]

^ Wow that really interesting! humm. Maybe I should try some softer springs in the rear and see how it goes.

quote Originally posted by fieroguru: Something isn't right in the front. The front springs have a motion ratio of about .5 (they are placed about 1/2 the way between the lower a-arm bushing and ball joint). With a 200 lb/in spring, the effective spring rate at the wheel is about 50 lb/in. So if you sit on a front fender, the suspension should go down. If it doesn't, something is binding, you are sitting on the bump stops, or the spring rate is much, much higher than 200 lb/in. In the rear the motion ratio is about .97, so your 275 spring rate, becomes about 258 lbs/in effective spring rate at the rear wheel.

Motion ratio at front is 0.69 by my measurements, making the wheel rate about 50% of the spring rate or about 100 lbs/in with a 200 lb/in spring, not 50.

[This message has been edited by mender (edited 03-15-2018).]

quote Originally posted by mender: Motion ratio at front is 0.69 by my measurements, making the wheel rate about 50% of the spring rate or about 100 lbs/in with a 200 lb/in spring, not 50.

I didn't have the info for the 84-87, so I was using the information for the 88. Thanks for providing the 84-87 info!