Rear suspension advice

[rdf]

Looking for advice on a new rear suspension setup.  Car is a 73 'Cuda, originally a 360 but now has a 493 Stroker in it with all factory suspension...needless to say, the car is like a unicorn on ice...rear end sways WAY too much and can't get the car over 40mph and feel comfortable about it.  I don't race it and never plan to, I just want a weekend driver that I can get on from time to time and feel like I have some control of the car.

Talked to many of my gear head friends in New England and they all pretty much say I need a 4-link rear suspension.  Thoughts?  Any recommendations on which type/kind/brand?  Here's what one of my friends sent me:
https://www.jegs.com/i/Ridetech/029/13027199/10002/-1?gclid=CjwKCAjwyY6pBhA9EiwAMzmfwSmBwm5zwcbjPgNYZD7DqJFv8Qbn_Gnh1geevclf4hGfuNVrRKPbfBoCjDcQAvD_BwE

[Brads70]

My initial thought is something is wrong? Nothing wrong with leaf spring suspension, surely won't be the cause of swaying and not being able to drive over 40mph?

How old are your tires? Air pressure? Defective tire? Brake issue?

[rdf]

My initial thought is something is wrong? Nothing wrong with leaf spring suspension, surely won't be the cause of swaying and not being able to drive over 40mph?

How old are your tires? Air pressure? Defective tire? Brake issue?

Leafs have been moved in to make room for a larger tire...tires are admittedly a tad old and balding but definitely enough air pressure in them.  Brakes are all fairly new with brand new brake lines and rebuilt master cylinder.  There is no sway bar in the car either, which I thought might be causing some of the issue.

[Brads70]

How much is it moved in? I ask as mine is moved in an 1" or so for the b-body width rear end.
Is the rear end mounted square in the chassis? You could simply use a couple jackstands and some string to get a rough idea? and/or measure the wheel base with a tape measure.  If the rear end is mounted cocked that will make it sway.

[rdf]

How much is it moved in? I ask as mine is moved in an 1" or so for the b-body width rear end.
Is the rear end mounted square in the chassis? You could simply use a couple jackstands and some string to get a rough idea? and/or measure the wheel base with a tape measure.  If the rear end is mounted cocked that will make it sway.

I'm not sure on exactly how much they're moved in but my rear rims are 15x9 with 6.5" of backspacing (Custom rims from Stockton Tire).  I will have to check the rest end to see if it's square...I'd like to think it is since the guy I took it to builds race cars for a living and has 2 of his own that he races...but, you never know.

Outside of all that, I assume if I did get something that's like what's in the link above, it would only improve responsiveness and handling (assumed if it's installed correctly)?

[rdf]

This might help give you an idea as to how far in the leafs are

[Bullitt-]

   Running air shocks?  I'll never forget back in the '70s being behind a Chevelle with air shocks and wide biased ply tires going around a curve when the rear started skipping sideways across the pavement.     

[Chryco Psycho]

4 link is not going to help .
Looks like the front of the springs are notched in to the frame rails .
Air shock are not helping for sure

[dodj]

My initial thought is something is wrong?

My leafs are moved in 1.5" each side and I have no problem getting over 40mph, or 70 for that matter. There is something wrong in the driveline setup, angles, or the  rear spring mounting, the springs, or your front end. Something. If you have to, mount a gopro or something under there while you drive to get visual evidence of what is happening.

I would be a little concerned about an 8 3/4 mopar diff surviving behind a 493 stroker though.......

[torredcuda]

Heavy duty leaf springs, rear sway bar and good shocks and you should be fine unless the rear is jacked up too high.

[HP2]

I've seen leaf spring cars have run at 140 mph with 9 second e.t.s without issue. You have different problems.

Do you have shocks? I don't see any in that picture. Leaf count? I can only see four leaves in each pack.  Those also look like  G60 bias ply dirt track tires. Are you mixing radials and bias ply tires?

[rdf]

I've seen leaf spring cars have run at 140 mph with 9 second e.t.s without issue. You have different problems.

Do you have shocks? I don't see any in that picture. Leaf count? I can only see four leaves in each pack.  Those also look like  G60 bias ply dirt track tires. Are you mixing radials and bias ply tires?

Yes, this pic was taken before they were put in....as others have said, they're just standard air shocks.  I'd have to look at the leaf count as I'm not too sure off the top of my head....and I'm 99% sure those are not dirt track tires....they came off my buddy's 69 Dart which is pretty much a daily driver for him.

[rdf]

Judging by the responses, it appears I should do a few things:

• Swap out the air shocks for something better (suggestions?)
• New sneakers on the rear (suggestions? drag radial?
• If no real improvement, add sway bar

I'm sure there's other things I could try but I think this is a good starting point.....thoughts?

[Bullitt-]

  I'd start with the simple no cost things... IF you still have the tires & wheels from before install them.... Let the air out of the air shocks, If the shock portion is still good they should suffice for a test.... Check that the rear brakes are not locking early.
  Change one thing at a time so you know what the result of any one thing is. 

[HP2]

I've seen leaf spring cars have run at 140 mph with 9 second e.t.s without issue. You have different problems.

Do you have shocks? I don't see any in that picture. Leaf count? I can only see four leaves in each pack.  Those also look like  G60 bias ply dirt track tires. Are you mixing radials and bias ply tires?

Yes, this pic was taken before they were put in....as others have said, they're just standard air shocks.  I'd have to look at the leaf count as I'm not too sure off the top of my head....and I'm 99% sure those are not dirt track tires....they came off my buddy's 69 Dart which is pretty much a daily driver for him.

They do have a tread pattern that looks ALOT like IMCA G60 competition tire, AND, they appear that they are bias ply. Bias ply tires, especially wide ones, are notoriously bad for hunting ruts in the road. If you rear feels like its steering on its own, those tires are not helping it at all. I'd try putting different wheel/tire combo under, even if it isn't the final size you want, just to see if the wandering goes away.

Example here: https://www.daymotorsports.com/shop-by/product/wheels-and-tires/american-racer-tire-g60-15-kk-704-x-tall/T-JWEV4