Rear suspension upgrades. 4 link?

[Dino]

I've been driving the car most of the time, except when there is snow on the road, and it's running really nice. The front alignment seems pretty good but I'll go over it again and play with the camber a bit more once it warms up. It tracks really nice doing 75-85. No issue there. But that rear suspension! It's always been rock hard. I sometimes feel like I'm driving a truck. It's unrelenting  and the crappy Michigan roads don't help. I have the, now discontinued, Edelbrock shocks, and the old stock leaf springs. Every rut or pothole makes the rear twitch, like the whole axle moves sideways an inch. The banging noise doesn't help either. No nothing is loose. If we had good roads this wouldn't be nearly as bad as it is, but this state has more potholes than potheads, and that's saying something.
Is anyone running a 4 link? I know they're not cheap, but if they could give me a more cushioned ride while maintaining good cornering manners, it might be the way to go.

[metallicareload99]

Do you have R/T springs or XP car springs? I'm definitely biased, but I can't imagine a 4 link setup holding up better than stock.

Now tuning for a better ride..... I bet you can adjust a 4 link to give you a better ride. Just way more adjustability available vs almost none. But you might have to go with some type of air spring to really get what you're after

The double adjustable shocks I'm using seem to help with ride quality on my car

[b5blue]

What rim/tire are you using? 

[Dino]

Do you have R/T springs or XP car springs? I'm definitely biased, but I can't imagine a 4 link setup holding up better than stock.

Now tuning for a better ride..... I bet you can adjust a 4 link to give you a better ride. Just way more adjustability available vs almost none. But you might have to go with some type of air spring to really get what you're after

The double adjustable shocks I'm using seem to help with ride quality on my car

RT springs. It's really a shame. The car is fine as long as the roads are, but they are far from it.

What rim/tire are you using? 

17" rims with 275/50 tires.

[b5blue]

That could be why.  I use 15's and the tires absorb a lot.

[Mike DC]

 
The stock RT leafs are too stiff for anything other than drag race launches.  XV Motorsports did all that chassis testing a few years back and they settled on a 5-leaf deal.  Bear in mind that any softening of the rear leafs would ideally need to be offset with a bit more stiffening of the rear sway bar (if you have one).   


The deeper issue is the unsprung weight of the axle.  That's the main reason why going over bumps feels like you're getting kicked in the ass.   

You can dump about 50-60 pounds of unsprung weight with fiberglass leaf springs.  But that conversion has some ins & outs.  It ideally needs lateral locator (panhard bar or watts).  Even stock steel leafs can benefit from that.  And you definitely need good responsive shocks with glass leafs.  The OEM steel leaf packs have a crude friction-shock damping effect that won't be there with fiberglass monoleafs. 


The geometry of an angled 4-link is decent. But it's not ideal and the design depends on a fair amount of rubber bushing flex.  The Chevelle & GTO and Fox Mustang guys (who have stock 4-links) will tell you all about it.   

If I was ditching the leaf setup, I would do 3-link + Panhard/watts.  The geometry is more stable (and simpler to adjust) and the bushings don't get worked as hard in normal movement.  It poses some packaging challenges but the final result is good.

[metallicareload99]

I definitely recall the XV testing suggesting softer springs. And the "rule" on springs I've been told is you only need them to be stiff enough to not bottom out the suspension

Despite all that, in my opinion, my 68 Charger with a Dana 60, rear swaybar, and CalTrac rear suspension rides okay over crappie roads. The split mono-leaf springs have @ least 200 lbs/inch rate with 305/45R18 tire and double adjustable shocks.

What with the State not having any money combined with the weather and seasons, I think the roads up here are pretty bad. I don't know if it's the tire or shocks but the ride seems decent all things considered.

Changing to a 4 link seems pretty extreme. Softer leaf springs and a rear swaybar might help. Even though Edelbrock shocks are supposed to be pretty good, there might be gains there with new shocks combined with lighter wheels 

[Dino]

That's good info guys, thanks! I can certainly try softer leafs first before doing anything drastic. I do have a rear sway bar still in the box. I never needed it with this setup but likely will with softer leafs.

[metallicareload99]

The OEM steel leaf packs have a crude friction-shock damping effect...

This is a good point, because the service manual instructions and stock bushing design is contrary to any "performance" practices. I.E. the movement of the suspension should be free from binding throughout its travel.

But when you crank down the front spring eye to 125 pound feet, and the bushing inner sleeve bites into the spring hanger the front pivot is all bound up. The effect would be to make the rear suspension feel even harsher

[Mike DC]

The wheel springs should only be as stiff as necessary to avoid excess flopping and hitting the bumpstops.   

The factory torsion bars & rear leafs on these cars (the RTs) are now considered too soft in the front and too stiff in the rear.   


To work with softer rear leafs it's good to add a small rear sway bar, to offset the lost roll stiffness.  The idea is to only soften the rear wheel spring rate below factory RT level.  Don't soften the total roll stiffness on the rearend.   (And if you've added a stiffer front sway bar and/or stiffer front torsion bars, then you could use more rear roll stiffness than OEM just to keep things in balance.)

Are you familiar with how wheel springs & sway bar rates add up, and the relationship of front vs rear roll stiffness, etc?  It takes a bit of understanding to avoid trouble.   Mismatching sway bars/etc can leave you with a car that wants to spin out. 

[Dino]

No, not really familiar with the math. I know the front sway bat needs to be bigger than the rear. I have old Addco bars. Front is, I believe, 1-1/8", and the rear is 7/8"

[Mike DC]

The general stuff is this:

#1, the total amount of roll stiffness at each end of the car is a combo of the wheel springs + the sway bar. 

#2, the softer end of the car (less roll stiffness) holds traction longer in a corner.  It's the stiffer end that runs out of grip first and starts to slide.   Playing with sway bars is the first-line way to tune the car for oversteer vs understeer. 


You can start to guess what this means in practice. If you stiffen the sway bar at one end, that changes the front/rear balance.  And it (counter-intuitively) makes the end that you upgraded more likely to slide first, even though the car's overall body-leaning might be reduced. 

The specific sway bar requirements are affected by a bunch of factors in the chassis design.  That's why front & rear sway bar sizes are usually pretty different.

So, yeah, if you soften the rear leafs on your car, and it already has an aftermarket-size front sway bar . . . it's good to install a small rear sway bar to keep things in balance.   Especially if you have stiffer-than-stock front torsion bars, which is also common (and recommended) these days. 

[Dino]

Thanks Mike! That's very helpful. I also want to change out the shock absorbers. I'm still running the Edelbrock IAS Classics. They're great at speed but not so forgiving in town it seems. Does anyone still make hydraulic shocks?

[b5blue]

Monroe Monro-matics.  https://www.rockauto.com/en/catalog/dodge,1969,charger,7.0l+426cid+v8,1078950,suspension,shock+absorber,7556

[Kern Dog]

Really? Monroe shocks?
No.
Bilstein, Hotchkis or Fox.
Monroes are for guys that just cruise around and rarely get over 1/3 throttle. If the OP is looking at a 4 link, he sure isn't going for K-mart type shocks.



$30 bucks for a shock on a car worth $80,000

[Dino]

I just ordered Viking Voyager shocks for all 4. They're double adjustable. I went with these because they have the most adjustability for cruising, while still having the option to tighten them if needed. It may be a while before I get them, but I'll post back with a review. I'm only going to change one thing at a time, or I won't know which components do what.