Chevelle rear suspension

[exwestracer]

Originally Posted by Roadbuster

Is your car lowered? This really changes the rear geometry. Much better anti squat but the roll center moves too much and is too high.

A Watts link fixes this. The Fays2 watts link allows for the exhaust to come out in the stock locations. Right now I just need the time to burn it all in.

I am welding in a Fays2 kit right now and the mock up cleared my dual exhaust. The pipes ran too close to the rear axle and I have to redo them (in 3 inch size) and they will exit in the stock location. If they ran up a little closer to the body I would have needed no modifications.

Now it's an excuse to redo the exhaust: 3 inch x-pipe with magnaflows exiting under the rear bumper is the plan.

Widowmaker has great fab skills

Without getting too deep into technical jargon, I'd like to point out that your rear suspension was never designed to use a Watts link as a lateral locator...for good reason. The triangulated 4 link rear suspension is it's own lateral locator. The V formed by the upper links controls side to side motion of the axle housing.

Here's the problem...Any sort of lateral locating device also defines the roll center height of the suspension. Makes sense...it's the only thing that isn't moving as the body rolls to the side. The upper control arms on the Chevelle locate the roll center at the imaginary intersection point of the V, around the height of the top of the housing (depending on ride height). When you install a Watts link as well, you have created a second roll center for the suspension to rotate around. It's pretty tough to get something to rotate around 2 different points...

I looked at the pictures of the Fays 2 setup, and they show the Watts link pivot under the Chevelle up at the top of the housing, which would work ok, but the suspension would want to bind the further the pivot was adjusted away from the intersection point of the upper links. if the upper links were changed to straight links, like the Impalas used, there would be no bind as they would not be locating the axle laterally.

Now, in a case of 2 wrongs making a right, binding the rear suspension on a Chevelle usually makes the car handle better; as they naturally understeer like pigs and locking the rear down makes them slide around a lot more and puts a grin on the drivers face... ...but it's still not correct from a geometry standpoint.

[jake72ss]

My idea is to eliminate the binding by adding either a torque arm as I mentioned earlier, or fabricating a bracket that mounts to the differential cover that would allow me to straighten out the upper links similarly to the steeda setup. In my own simple way it seems to me that if the upper links stay at the same angle from a side view, that the critical points such as instant center, and such wouldn't change it would just allow me to mount a watts or panhard bar to relocate the roll center height. I may be way off and I am not about to cut on my car just want to get some feedback on the ideas floating around in my head.

[jake72ss]

http://image.automotive.com/f/projec...suspension.jpg
If I fabricated a torque arm like this what would I need to keep in mind, where would be the best location for the front mounting point? I mean how bad could I screw things up, what would I trade off by doing this?


http://www.steeda.com/store/images/p...stem-mus-1.jpg

The Steeda 5 link is designed for fox mustangs but since their rear suspension is similar to A bodies that is where I came up with this.

[exwestracer]

Originally Posted by jake72ss

My idea is to eliminate the binding by adding either a torque arm as I mentioned earlier, or fabricating a bracket that mounts to the differential cover that would allow me to straighten out the upper links similarly to the steeda setup. In my own simple way it seems to me that if the upper links stay at the same angle from a side view, that the critical points such as instant center, and such wouldn't change it would just allow me to mount a watts or panhard bar to relocate the roll center height. I may be way off and I am not about to cut on my car just want to get some feedback on the ideas floating around in my head.

Ok. You had also mentioned "or add a watts link or panhard rod with the stock configuration", which was my concern. Personally, I'm a big fan of the torque arm rear suspension. Other than a little more unsprung weight, it is a very simple and effective design. Your main problem will be mounting the arm securely to that cast center section of the rear end housing. There are obviously kits out there to do this. Most use a beefy aluminum rear cover with the arm mounts built in.


As far as the front mount location, your options are pretty limited with that perimeter frame design. Box the frame around the trans crossmember, beef up the crossmember itself, and mount the front pivot to that. Just remember the torque arm has to be free to move front to rear slightly and the front pivot must have some rotation capability, but it doesn't need much. Something like a leaf spring shackle extending up from the crossmember with a large rubber bushing or heim end on the arm should work fine.

Then just remove your stock upper links, install that Watts link, and go.

[Blake Foster]

Our torque arm could easily be made to fit the A body, all that would need to be fabed is a front torque arm mount
we could do a combination of the rear coil over conversion, torque arm, and lower trailing arms and sway bar.
it would be almost identical to our F body torque arm set up.

[ProTouring442]

Originally Posted by killer69

Our torque arm could easily be made to fit the A body, all that would need to be fabed is a front torque arm mount
we could do a combination of the rear coil over conversion, torque arm, and lower trailing arms and sway bar.
it would be almost identical to our F body torque arm set up.

Don't happen to make that for a 9" do ya? My 442 has a 9" and I would love to go the Torque Arm route.

Shiny Side Up!
Bill

[Blake Foster]

Originally Posted by ProTouring442

Don't happen to make that for a 9" do ya? My 442 has a 9" and I would love to go the Torque Arm route.

Shiny Side Up!
Bill

sure do

[Derek69SS]

Originally Posted by exwestracer

Without getting too deep into technical jargon, I'd like to point out that your rear suspension was never designed to use a Watts link as a lateral locator...for good reason. The triangulated 4 link rear suspension is it's own lateral locator. The V formed by the upper links controls side to side motion of the axle housing.

Here's the problem...Any sort of lateral locating device also defines the roll center height of the suspension. Makes sense...it's the only thing that isn't moving as the body rolls to the side. The upper control arms on the Chevelle locate the roll center at the imaginary intersection point of the V, around the height of the top of the housing (depending on ride height). When you install a Watts link as well, you have created a second roll center for the suspension to rotate around. It's pretty tough to get something to rotate around 2 different points...

I looked at the pictures of the Fays 2 setup, and they show the Watts link pivot under the Chevelle up at the top of the housing, which would work ok, but the suspension would want to bind the further the pivot was adjusted away from the intersection point of the upper links. if the upper links were changed to straight links, like the Impalas used, there would be no bind as they would not be locating the axle laterally.

Now, in a case of 2 wrongs making a right, binding the rear suspension on a Chevelle usually makes the car handle better; as they naturally understeer like pigs and locking the rear down makes them slide around a lot more and puts a grin on the drivers face... ...but it's still not correct from a geometry standpoint.

I agree, but some compliance from the use of rubber bushings in the upper housing ears would be enough to eliminate most of the bind through the useful travel of a well set up PT car... that very minimal amount of bind would be a perfectly acceptable trade-off for a lower roll center height and no roll center migration.

Torque-Arm would undoubtedly be a better solution though.

[exwestracer]

Originally Posted by Derek69SS

I agree, but some compliance from the use of rubber bushings in the upper housing ears would be enough to eliminate most of the bind through the useful travel of a well set up PT car...

True, IF you stuck with rubber up top. You'd just kill the rubber bushings a little faster. At that point though, I think I'd just yank the uppers and get on with it..3 link or tq arm.

[jake72ss]

Would I sacrifice anything by going to a torque arm, it looks like the easiest to package. What would happen to anti- squat, etc? Is there a calculation to use to determine the best overall length, forward mounting location, etc?