A-body chassis dynamics, handling

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MopaR&D

MopaR&D

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I was wondering about some general handling topics in relation to our beloved A-bodies. Now I almost always see guys building road-race Barracudas (64-69), with one exception being the Mopar Action "Green Brick" '70 Valiant. Is there a particular reason for this? Also, it seems like Dusters have a rear overhang quite a bit bigger than the other A-body models that would have a negative effect on handling; is there any truth to this?

On a more detailed note, how do shock-absorbers affect handling? I believe the shocks in my Duster are shot as it would sway and wobble like a b!tch going over bumps (sometimes almost out of control if turning at the same time), and I could get the whole car into a wobble motion just by pressing down on the fender a bunch of times. Also, how noticeable of a difference should a front sway bar make in handling? I noticed a very slight difference after putting my bar in but I'm pretty sure that was just because I was running up against the bump-stops when going around corners at speed and the bar wasn't mounted very well (endlinks pointing out and forwards, and center mounts able to flex).

Sorry for all the questions, but they have been bouncing around in my head for weeks and I want to learn more about suspension tuning.
 
They're all pretty much the same basic design and similar weights, so what works on one A-body will work on another. Most of them have quite a bit of rear overhang. I don't have any numbers for the Duster, but it's not significantly different from other A-bodies. I've seen Darts and Dusters built for handling as well as Barracudas.

Shock absorbers are designed to damp out that wobble motion. The best ones will do this without contributing excessive harshness to the ride. I have a set of KYBs, and they improve handling over stock, but they also make the ride a lot rougher. I've heard good things about the Edelbrock IAS line for a street car, and would probably use QA1s if I were buying shocks for a handling car, but I currently don't have any personal experience with either one.

Good sway bars should make quite a reduction in body roll; I'm running an Addco front bar on my Dart and it really reduced the body roll in spite of a rather poorly designed mounting system.

If you were hitting the bump stops on corners, you'll probably be able to feel it. Not necessarily as a bump, but as the car stiffening up suddenly. And you have other problems. If the car has been lowered, it probably needs stiffer torsion bars.
 
The best changes I have made to the handling of my car so far are stiffer springs and torsion bars, new gas charged shocks (Monroe-matics) and sub-frame connectors. With just these changes, handling changed like it was a different car. Not a road race car, but not scary to drive over dips and twists in the highway!

I plan on adding a front sway bar when I convert to disc brakes.
 
I've actually made the decision to do the deal. I'm going to convert my 67 Cuda into a vintage road race car. I do have a fair amount of road race experience, but mostly in other vintage European cars.

There are many different issues I see with the A body cars to make them handle. On a basic level we need to make the chassis stiff, so that we isolate the suspension and it's ability to work.

To do that, I am planning on sub frame connectors and a full roll cage, tying in the suspension points.

Then it's about reinforcing the suspension pieces. There seems to be a fair amount written on the upper and lower a-arms and how weak they are. Seems like you can plate the lowers and buy tubular uppers (if you get he uppers, get the double adjustable ones, so you can adjust camber and caster. (I need to figure out how to make the uppers look vintage.....) The front suspension uses Torsion bars, which act just like a spring. The shock dampens the osculations. On a race car you can (if you have adjustable shocks) modify the compression speed (downward action of the shock) and rebound (upward speed). This is very important as it can really effect the way the car handles.

(insert)

Remember when a car is traveling/racing, there are 4 contact patches that are each the size of a sneaker. The car weighs 3000lbs, so for sake of argument say 750lbs per wheel. As the car rolls from one side to the other when turning, and combined with front to rear weight transfer (braking or accelerating), you can move a lot of weight around the car and ultimately put too much weight on one wheel/tire, compared to it's ability to stick to the ground. You utilize your driving skill and the suspension to manage this effect, as ideally you want equal amount of weight on each tire at all times. That's where skill and suspension setup come into play. The job of the driver is to manage the weight transfer to make sure you don't overload the car. This is an over simplification, as we could write for years about it, but hopefully just a basic picture. If you want more details on handling and it's effects there are many books. There is a great basic flip book by Carroll Smith called "engineer in your pocket" that covers cause and effect. fun easy read.

(Back to point)

So your car bobs up and down uncontrollably, so you know the T bars are "springing" the car up and down, but the shocks are not controlling it. So Start with new shocks. Don't forget to check you tire pressure, as the air in your tires are also a spring too.

You may know that Carrol Shelby moved the upper a-arms in the Shelby Mustangs and that changed the path the wheel moved on and made a dramatic difference in the handling of the cars. I need to find someone who had down work on A bodies to see if we have to move the "pick-up" points around to get the same advantages.

It is also important to make sure that the suspension mounting points are secure (tight) and all busings are in good shape, as that can also effect how the suspension moves. Also check your front wheel bearings (jack up the car, grab the wheel at 9:00 and 3:00 and/or 12/6 and see if there is any play. There should only be about 1/32ths. Also these cars are renown for bad Idler arms and pinion arms. again, check for play and replace if necessary.

This is just a glancing blow at many issues here, but I hope it's a good start!

Good luck
 
I'm glad you brought up the idler arm thing, because I'm pretty sure I need a new bushing for that. I recently rebuilt the front suspension but there wasn't too much difference in the way it drove; just a bit less "floaty" on the highway. I just got the latest Summit catalog, and in the suspension section they listed Koni shocks; aren't those supposed to be really good?

As for the sway bar, I'm seriously thinking about welding the mount brackets to the K-member and playing around with the mounting and end-links a bit to stiffen it up. BTW the front wheel bearings are in okay shape, I recently readjusted them and put new grease in them.

One thing that was stupid of me was that I didn't take out the "fender support" brace things from the '75 Duster parts car I had for a while. They probably would've stiffened the car up a bit.
 
Koni shocks can be great or just OK. depends on the model and how the shock is built. (shocks on race cars can retail at $7500, yet I can still buy shocks for my Newport for 35 bucks.....) it has to do with how stiff the body is, size and dia of the rod, valving, adjustability etc...

I was reading last night that Koni has made adjustable shocks or some vantage A body cars, so you should try to reach out to them and ask.

i don't think you can replace the bushing on the Idler and Pitmen, just put new ones in, they are only about 100 bucks from just suspension. Well worth it.

Stiffer valved shocks and bigger t bars will help the floaty thing a lot. Do you know what size your T bars are?

Concerning the Sway bar thing. Be very careful about moving the mounting points around. it will have a dramatic effect on the performance of the bar. and remember, the bar will not help the float feeling. bars only come into play after you have "turned in" the car. The reason for bars is to fine tune the chassis after turn in, as the car heads towards apex or exits apex, but that's a discussion for another thread......It's the shocks and T-bars that effect turn in and "float" (as the bars are not doing anything if the car is going straight - unless you have the bars loaded and your corner weights are off...)
 
I have the stock torsion bars for a 318 A-body; I don't remember the size, but they are woefully inadequate. After thinking about it the Konis might be too expensive and I may go with the Edelbrock Performer IAS shocks; they seem to be the best bang-for-the-buck and have gotten very good reviews.

About the sway bar, I installed it after I rebuilt the front suspension and had it lowered a smidge and aligned. I barely noticed a difference in body roll when going through a corner before and after, and when jouncing one side of the front of the car I can definitely see the mounts moving at least a couple mm (I'd imagine they are supposed to stay firmly anchored). I also didn't want to move the mounting points, just change the setup of the mounts themselves so that they would flex less.
 
Yea, if the mount is moving, it needs to be strengthened. If you are looking for better handling then the small T-bar will not work. my understanding is the largest T-bar available is about 1.14" in dia. That, plus some new shocks (get some form of HD shock to compensate for the larger T-bar). Then make sure your rear springs are the stiff ones then go for a ride...
 
One can go too stiff on springs. As said before, the weight of the car moves around, and that affects grip. More weight on the outside tires improves grip, but not more than the sideways centrifugal forces. Stiffer springs reduce body sway, and body sway causes the tires to lean in relation to the ground. Stock '60 type suspensions were very soft, and caused excessive body sway and excessive positive camber on the outside tires. A lowered A-body has more camber gain than when at stock height. As the tire moves upward, the upper ball joint moves toward the center of the car faster than the lower ball joint due to the angle they are at, and the fact that the upper arm is shorter than the lower arm. This is similar to what happens to the early Shelby GT350s with their 1" lowered upper control arm mounting holes. As for shocks, I have a set of QA1 Stocker Stars sitting in their boxes that I need to install. I've heard a lot of good things about them. I've heard good things about Konis too, but that they are discontinued. I've heard a few bad things about Edelbrocks, and lots of bad things about KYB.
 
Here is some good reading material on Mopar suspensions, mostly A-Body:

How To Build The Ultimate Super Street/Track Mopar
(Dodge/Plymouth Performance Volume 2)
by Mike Martin S-A Design No. 20-2

Direct Connection Racing Manuals
#15 P4007917
#27 P4007924
#30 P4007927
Or full set PN4007933
 
1cerberus4u said:
I was reading last night that Koni has made adjustable shocks or some vantage A body cars, so you should try to reach out to them and ask.
Click to expand...

They did at one point, but when I asked last year they were discontinued. They could, however, revalve their drag shocks into road race shocks and get you something that would work well, just be more expensive.

For an off the shelf max performance shock, the QA1s seem like a good possibility.
 
The Mustang needed a lot more work than an a-body because the design was so poor. I have never heard of moving the mount points on a Mopar, except for drag racing (altered wheelbase cars).
 
Jim Lusk said:
The Mustang needed a lot more work than an a-body because the design was so poor. I have never heard of moving the mount points on a Mopar, except for drag racing (altered wheelbase cars).
Click to expand...

You got that right. I took a look at my neighbor's '67 Mustang when he was rebuilding his front end and compared to my Duster's front end it looked like it belonged on a Radio Flyer wagon more than a car. I think the sway bar might've been an integral load-bearing component by the way it looked!

I don't know if I'd need a max-perf. shock anytime soon anyway. With even decent performance shocks and higher-rate T-bars I think I'd start running out of rubber. I'm running the stock 14" steelies with 70-series BFG Radial T/A's!
 
375inStroke said:
As for shocks, I have a set of QA1 Stocker Stars sitting in their boxes that I need to install. I've heard a lot of good things about them. I've heard good things about Konis too, but that they are discontinued. I've heard a few bad things about Edelbrocks, and lots of bad things about KYB.
Click to expand...

Are the KYB's that bad for a street car? I was going to get the Gas-adjust all around on my 65 barracuda. I've used their AGX adjustables on a Miata and they seem to make a nice shock.
 
My son has KYBs on his 67 Barracuda (383/4sp BIG t-bars, sway bars) and I never felt that the ride was unacceptable. Certainly wasn't near as harsh as my 79 W200.
 
A set of KYB shocks are close to half the price of one QA1 2-way adjustable. Could they really be worth a crap? I haven't used them. Just passing along hearsay.
 
375inStroke said:
As for shocks, I have a set of QA1 Stocker Stars sitting in their boxes that I need to install.
Click to expand...

Are these for an A-body? Do you have a part number? I looked at Summit and they don't seem to list one for a Mopar application.

On the same note, I see Firm Feel lists a Koni for an A-body - anybody have any experience with these or is Firm Feel listing a discontinued item? I will end up calling them for some other items, just thought somebody might know.

TIA
 
Red Sled said:
On the same note, I see Firm Feel lists a Koni for an A-body - anybody have any experience with these or is Firm Feel listing a discontinued item? I will end up calling them for some other items, just thought somebody might know.
Click to expand...

Well, now I am talking to myself (again LOL), but I just got off the phone with Dick at Firm Feel and they no longer carry the Koni's. They are now selling non-adjustable Bilesteins (sp?) for the A-body application. Don't know how they compare to the QA's, just passing along some info.
 
There was this one guy who built a vintage GT road-race-style '66 Barracuda, you could probably do a Google search for it (I forget the website). I know there's also another member on here who road races his 2nd-gen Barracuda.
 
I have the Original Window sticker and my car still has the Factory HD Spring Package. and 4 piston Kelsey Hayes Discs & Front Anti Roll Bar. Big drums (10.5), Sure-Grip 8-3/4 & Close ratio A833 (Inland Shifter). Handles through 225 60 R14 up front and 245 60 R15s out back (110 Wheelbase) Rallye Wheels all the way! There is no way to fit any Larger rears in that hole without Mods. Mine barely rub on both sides (On Up-Hills mostly)

I am looking into Fabricating a front lip Spoiler for High speed Stability and Extra Cooling for Radiator. Front ends Floats a lot (SCARY!!!) around 80MPH it Becomes more like Sailing! Yay I love sailing!!! But not in my Sportscar. So Spoiler here we come.

My brother bought me a full set of ENERGY SUSPENSION poly busings... YESS!!! Cant wait! Plan on wire wheeling and painting all Components black upon re-install.

I have a budy with a 69 Dart GT who has the 225 with a 390cfm 4B Wilwood 6 & 4 piston discs and Independent Rear suspention out of a Thunderbird Sport coupe or something. anyways We Rally hard. My buddies 2005 S2000 is right in step up Highway 9 (2nd & 3rd Gears) He is always impressed by the 40+ year old American Technology can hand with his Formula Inspired Japanese V-Tech Super Trick 6 Speed. And everyone goes, "NO way they weigh the same!" 2900lbs. and my Dart has back seats and a Big Trunk!!! Ha that is so fun! Our other buddy Stuffed his 05 S2K so we no longer run in a 4pack.
 
Find Tom Condran's book "Performance Handling for Classic Mopars." Seperates the 'real' from the 'get real.' Helluva good guy,too. Spax adjustable shocks are available through British American Transfer out of Sarasota,Fl. They are listed under Chrysler Australia; call Eric @ (941)355-0005 if you are interested.
 
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