I'm trying to sort out some handling issues on my 1971 Satellite 4-door police car clone. I've tried to make a decent-driving car, within the constraints of 15-inch tires. Here's what I've got in a nutshell:

FRONT:
1.03" T-bars
Suspension rebuilt with Moog hard parts
Firm Feel upper control arms
Steering box from Firm Feel
Polyurethane LCA bushings
Helwig anti sway bar. I think it's 1-1/8, it's been a while since I installed it and the memory fades
Koni shocks
225-70-R15 Cooper Cobra tires (being a police car clone, I'm stuck with 15" wheels)
Alignment is 1/2 degree negative camber, 5 degrees positive caster, and I do not remember where the toe-in is set.


REAR:
6-leaf Mopar Performance springs, intended for the left side of late-60's 440 & Hemi B-bodies. I can get the part number if needed.
Helwig 3-way adjustable anti sway bar. I think it's 3/4, it's been a while since I installed it and the memory fades
Koni shocks
235-70-R15 Cooper Cobra tires (being a police car clone, I'm stuck with 15" wheels)

The problem is when driving on a straight road with slight dips in the pavement, the rear end is "bouncy" for lack of a better term. Constant, tiny up-and-down movement. Harsh dips are handled much more effectively and satisfactorily than tiny ones. I've cranked the Konis from one extreme to the other with many stops in between, and the problem cannot be rectified. So yesterday, I pulled the QA-1 double adjustable shocks off another car and put them on the Satellite and will see if they can help the problem.

A FEW OBSERVATIONS AND QUESTIONS:

The rear springs give the impression that they are too stiff. I have removed one and two leaves for trial. That seems to help but the car squats too low in the rear. I'm confused though, as these same springs were factory-installed on 60's cars with bias ply tires. Wouldn't radials want more, not less spring rate? BTW, I have removed the U-bolts and checked that both saddles sit squarely on the spring perches... I understand that if the rear end were in a bind here, similar symptoms would occur. I could just remove two leaves and get the springs re-arched (or buy different springs) but I'm somewhat surprised that these springs exhibit the symptoms I'm seeing.

Compressing the rear suspension by pushing the rear bumper down causes the tires to visibly compress. I've tried 25 to 38 pounds of air in them... it seems to be happier with less inflation. The fact that the tires compress and not the springs also seems to indicate too-stiff rear springs.

I have the QA-1 shocks on now and I'm thinking of trying a low number on the compression damping and a high number on the rebound damping, which would seem to make sense if springs are too stiff.



I'm way past my knowledge and experience in this area, so any advice is appreciated.

Jim

Lets see what I can throw out.

IIRC, and that's no guarantee these days, the XHD springs are around 160# rate. So not radical high, not really low. I doubt they are too high for your vehicle. Remember that if the springs take 160# of pressure to compress one inch and your tires have 35# or air supporting them, that is a huge difference in resistance, especially with a 70 series tire. I wouldn't worry about this aspect.

I wouldn't say a radial wants more or less spring than a bias ply as it all part of the combo. If anything, the construction of a radial may allow a softer rate to get similar performance because of sidewall compliance, but that's tire theory way beyond my pay grade.

Oscillation or porpoising is typically because of match front to rear spring frequency, not rates. But, you say these are relatively minor oscillations of small road irregularities instead of major dips, so I wouldn't say this is the issue.

I might lean towards an issue with high speed resistance of the shock. Shocks control spring travel with high speed valving, like bumps and ruts, and low speed valving, dips on the road or cornering. These are two separate values built in to the shock. Single adjustable shocks are designed to address overall compression or rebound and do not differentiate between high and low speed pistons speeds within the shock. To generate enough high speed resistance might require cranking the shock up so high that the low speed resistance is now producing a rough ride.

Since you have gone to a double adjustable now, I agree that you might want to try softening up the bump to allow it to soak up the hit and firm up the rebound to push it back into the pavement faster.

Thank you, TC@HP2.

Today, I removed the smallest of the leaves in the XHD springs (thank you for reminding me what they were called) and that made an improvement. I had actually done this once before when the Konis were on the rear and didn't see the improvement I saw today. The shortest two leaves are very easy to remove so I might continue down this path, possibly removing the next-longest and replacing it with the shortest. I will add that the spring pack is perfectly flat when statically loaded my the car now. I might get to the point that it is arched upward if I remove too many leaves, but I suppose I'll cross that bridge when I come to it.


I might have gone down a rabbit hole, but right now I have the shocks set at:
Compression damping = 2 clicks (of 18 possible)
Rebound damping = 10 clicks (of 18 possible)

Having never played with double adjustable shocks, especially using them as what could be a band aid for some other problem, I don't know if those settings pass the sanity test or not.