Softer Shock absorber options

MopaR&D said
I'm sure @72bluNblu or @BergmanAutoCraft could explain it better but I'll give it a shot...

The first key thing to understand when dealing with shocks is that every vibrating system has a "natural frequency". This depends on the unsprung weight (wheel and tire, brakes, spindle etc for front or the entire rear axle), sprung weight (car itself) and the rate or stiffness of the spring. The system needs to have damping (shock absorbers on a car) in order to stop it from vibrating virtually forever or having the tires leave contact with the pavement and the required damping rate is based on the natural frequency. If the damping rate is too low (shocks are too soft) the car will bounce a lot after hitting bumps and have bad recovery time when making sharp turns. If it's too high the car will ride stiff and the springs won't be able to do their job properly.

So with that said different cars in different conditions need shocks with different damping rates. Unfortunately for classic Mopars you basically have cheap shocks that are either very soft/low damping rate to match up with factory spring rates or too firm like the KYBs. The higher-end shocks like Bilsteins in a nutshell have better control and react to different conditions better, as in going over potholes vs. driving fast on a twisty road because the way they work internally is more sophisticated. This is why adjustable shocks exist; when you want maximum suspension control you can dial-in the damping rate to match up with the spring rate and driving conditions. I actually plan to get adjustable shocks for my Duster since I do handling-oriented amateur racing stuff with it and the current stock replacements don't do jack with my 1.14" torsion bars, front and rear sway bars and Hotchkis rear springs.

KYB Gas-a-justs are good-quality shocks but they have progressive valving meaning the damping force is highest when the wheel is moving fast (over bumps or potholes) which is the opposite of what you want. In my experience they work best on trucks and 4x4s with big tires and lots of unsprung weight to keep things bouncing around too much. Bilsteins or other brands of high-performance car shocks have digressive valving which work the opposite; soft going over bumps but firms things up in hard cornering to keep the car stable and minimize unwanted weight transfer, like body lean.

So to the OP after all that, lol... if you just like to cruise your car and aren't concerned with making it handle super well go with some cheap Monroes or Gabriels, your ride will be much softer. Only downside in my experience is they're built like crap and like to blow out after not very long. I've had shocks from both brands go out within months of installing them. I know KYB makes an OE-replacement line of shocks called Excel-G which do ride soft, I've used them on other vehicles but I'm not sure if they have them in the right sizes for classic Mopars. In the past when I've searched by year/make/model for my Duster the Excel-G's didn't come up.

That's a great explanation. Don't think I could have done it any better.

The bottom line is that you want your springs and shocks to match, so that your suspension reaction is close to what they call "critically damped". Meaning, the suspension travels through its full range of motion for a given input (allowing it to suck up the bump while keeping the wheel fully planted on the ground), without letting the spring continue to oscillate after the input (allowing the wheel to remain in contact with the ground after the input is over and ready to track the next input). Underdamped suspension allows the springs to keep oscillating, most people have experienced because it's what you get with worn out shocks. You hit the bump and move down the road and the car is still riding like a wave. Overdamped is the opposite, the shock stops the suspension movement too quickly. That gives a harsh ride, and can cause a loss of traction because it will bounce the car rather than the suspension. The whole idea is to maximize the pressure of the tire on the road throughout the entire event so you have the best traction.

mvh said
I would think that with the really big t-bars, you would scarcely notice the front shocks coming into play. You'd probably notice it more in the rear. My convertible has the stock slant six springs all around and white KYBs, and I think the ride is fine. It really soaks up the big potholes and heaves on poorly-maintained back roads. My FB has big block t-bars and HD rear springs with the same shocks, and it is much stiffer over bumps — you could definitely call it harsh. It also has front and rear sway bars, but those only come into effect if you are hitting the bump with one wheel instead of both wheels. But it really stiffens up the single-corner pothole impacts — my setup has no rubber in the end links.

For a smooth ride, I have heard Monro Sens-A-Trak recommended. No personal experience.

Completely wrong. The larger the torsion bars the more important the shocks are to damp the reaction of the bars. Otherwise you have a suspension that's spring dominated, the pressure of your tires on the road oscillates with the springs instead of being maximized, so, you give up traction.

What you run on your convertible is basically what people that think that KYB's are good shocks run. You run a REALLY soft spring, with a really stiff shock. The result is an overdamped suspension system. From a subjective standpoint it doesn't feel terrible, because your stiff shocks are counteracting your soft springs. But the suspension reaction is not ideal for good handling, rather than working together to improve your handling your suspension components are fighting each other.

Your car with big block torsion bars rides stiff because KYB's are horrible. Their simple design results in a progressive response like MopaR&D explained. Basically, the harder/faster you hit the KYB's the stiffer they get. Which makes them completely awful for larger torsion bars. The overdamping gets worse, making the ride more harsh. At the extreme, they don't let the suspension travel as it should, which means you lose traction as the wheels don't track the road.

Ricks70Duster340 said
James, I have the white KYB's all around on my '70 Duster small block. They are a bit stiff, but thought I had to deal with that. My biggest issue is when I go over a dip in the road, the front end sometimes bottoms out. I have the ride height set pretty high because I am using the '73 front sway bar with the QA1 LCA's and it sits much lower than the OE sway bar. I would not mind spending the money for better shocks, but I would like to get something that will ride well but deal with the road dips.

Exactly the problem with soft springs and stiff shocks. The ride quality is stiff because the suspension is overdamped, BUT, the springs are really soft so on big bumps/dips the suspension still bottoms out because you don't have enough wheel rate to control the input and the shocks can't compensate and keep the suspension from bottoming.

You need larger torsion bars to keep the suspension from bottoming out, and better shocks to control the larger bars so your ride quality doesn't suffer.