OK, so I was setting up my rear suspension for a soon to come track visit. The previous owner(s) have done most of the suspension mods, but who knows if they knew what they were doing, so I was going to get a good starting point, such as driveline angle, LCA angles, and center the axle.

FYI, setup includes: UMI long slip-type T/A, unknown brand DA rod-ended LCAs, unknown brand DA rod-ended PHB, Hotchkis lowering springs, and unknown shocks. The Strange 12-bolt has the LCA relocation brackets.

I was reading on ways to center the axle, I know it has been off for quite some time. On some threads, I read to drop a line from each rear fender and measure from the wheel cap to the line and center it to the body. Sounds easy enough, right? Wrong... My passenger bump-stop was already rubbing the tire, 315/35/17 Nittos on 9.5" wide wheels, and the measurements read 2 1/2" on the PS and 3" on the DS. IF I were to move the axle a 1/4" towards the DS to center it with the body, the bump-stop would dig even deeper into the PS rear tire. So I got out the grinder and ground off quite a bit of material around the PS bump-stop. All I could remove was enough where they were just touching with the axle centered to the body.

This all seemed a little weird, my clearances anyway. So I starting making frame measurements and noticed this uni-body subframe was all kinds of tweaked, not surprised, as this car has been sideways over a curb @ 35-40 MPH. I looked at the angles of the LCAs and the DS was like this, / from a birds eye view, angled inward from axle to chassis/uni-body. The PS was about straight with the subframe connectors. I was like, WTF?? So I then measured the LCA brackets and they are off center by about 1/8" which isn't too bad, I guess. So I said F* it and figured it would probably be best to get the LCAs as parallel as possible with the subframe, considering the LCAs are what actually apply the forces to move me forward under hard launch.

I ended up moving the axle 1/4" more towards the PS from the original measurements, which would of given me plenty of clearance with the bump-stop had I have not whipped out the grinder. I just have more than enough now. I put a straight edge on the rear brake rotors that was in-line with the LCAs and measured distances between the straight edge and LCA as various points moving from the axle connection point towards the chassis/subframe connection point. I knew they wouldn't be the same measurements from point to point between DS and PS, as the LCA brackets were off, but as long as the change in length was the same, the angles are the same. Measuring from the axle towards the chassis gave me about 1/8" difference in length on each side, ie 8" between the straight edge and LCA close to the axle and 8 1/8" between the straight edge and LCA close to the chassis/subframe. So the LCAs look more like / \ from a bird's eye view. The slashes are exaggerated as they are as close to parallel as possible. The body to wheel center caps now read 2 1/4" on the PS and 3 1/4" on the DS. So the axle is now more off-center with the body, but is straight to the chassis/subframe.

What do ya'll think for a starting point on the launch dial-in process? Did I do it right? Or should I have of made it center with the body? Sorry for the long read, I like to be as thorough as possible, to eliminate confusion in my technical questions/posts.

 

anyone?

 

bring it to a shop and have them do a 4 wheel alignment. If you can't then have the front wheels aligned and then align the rear end with respect to the front wheels. A tape and a square are your friend.

 

So you're saying, align them with the front tires, not the body, and not the frame...? I have both tape and numerous sized squares, I am just trying to figure out what component(s) to center the axle to.

 

I'm not the expert, but makes sense to me and that's how i did it.

 

See, that doesn't make sense to me, it used to, but the more I thought about it, the less it made sense. I would figure you would want the LCAs as parallel as possible which means centering the axle to the frame.

Anyone else have input on this?

 

I have been told by suspension guys who setup promod cars that you shouldn't center the rear to the fenders but should align it to the underbody.

Here's what they recommeneded:

"first don't go off your frame rails! go off of center, You need to find the center of your car aprox 2-3 feet infront of your axle, there are several ways to do this. I find comon points side to side that the manufacture used to Jig the car during build(if your rocker pinch welds arn't beat up use them) I usually find 2 points near the front, and 2 near the rear, and plumb bob down to the floor and mark the points then measure side to side , find the center of those 2 points and mark center, I usually use a laser at that point to make a line from the front to rear of the car, I use a laser because it will project a line on the floor and the car, once I have the center line, I mark center on the car about 2-3 feet infront of the axel. once I've marked center, I measure from the lower control arm rear bolt to the center point I've marked, once your measurement are the same side to side your rear is centered and square, then you adjust your pinion angle by shortening or lengthening your upper control arms equally(the same amount of turns) I have used this method on 100's of set ups you cant go wrong with triangulation."

-Mark

 

Thanks, thats much more along the lines of what I thought. I mean, what does the body have to do with anything, especially when its not square? I will verify the center using the pinch weld/jacking points and see what I come up with. Hopefully, I am pretty good as it sits. We shall see.

 

I see, well I guess I'm assuming the front wheels are already centered with respect to the frame. Anyways, when I did mine, the rear was square to the front wheels and equal length from the rear quarterpanels -front to back and side to side (which gave me some extra comfort).