Mark 3 4 Wheel Alignment

[Porky]

Good morning everyone, I am in the process of finishing up a partially completed no donor, IRS Mark 3 kit that I bought here on Long Island. It's in the go kart stage and I'm getting ready to mount the body. The car has 17 inch 315s on the rear and 275s on the front. While I was looking at it in the driveway the other day from the rear I noticed that the rear and front wheels are not lined up. On the pass side, the outer edge of the wheels are in line, front to back and on the drivers side, the wheel center lines are lined up front to back. Both wheels rub on the wheel wells slightly with more of a rub on the pass side.

I have read many posts on doing a four wheel alignment and I realize now that the PO must not have done this. I have set up strings off of 3/4 inch EMT supported by the front and back quick jacks and I'm prepared to make the adjustments to the IRS to make things right. I have two simple questions.

1. Is the correct rotor to rotor rear wheel dimension 59 or 59.5 inches?

2. When properly aligned, will the wheels front to back line up by their outer edges or their center lines.

I know these are basic questions but I want to make sure I start with a proper understanding of how this needs to end up when complete.

Thanks in advance for all of your help.

Joe

[karlos]

When I set up my IRS back in August I used a track width of 59-1/4" per FFR's recommendation.

I suspect the misalignment you're seeing is a result of not having set the rear track width equally side-to-side. It should measure 29-5/8" from the center to each side assuming a total track width of 59-1/4". In order to establish this measurement you'll need to start by locating and marking the centerline of the chassis. The two horizontal 4-inch tubes at the front and rear of the chassis work well for this purpose. Use a plumb bob to transfer the centerline to the floor, and then from the floor back up to the trammel bars that hold the strings at the front and the back of the chassis. End result is two strings that are parallel to the centerline of the chassis as well as to each other. You can then equalize the side-to-side track width by measuring to the strings on each side. This is a tedious and time consuming process, as it's hard to simultaneously get both measurements to come in at the same time. I ended up with 59-1/4" overall and equal side-to-side within 1/8". To exactly equalize side-to-side track width while maintaining a total width of 59.25", one side would need to decrease by 1/16" and the other side would need to increase by 1/16". I decided that such small corrections were not really worth messing with.

To my knowledge the track width in the front is not adjustable. So my suggestion is to set the rear up properly and let the relationship between the front and the rear wind up where it may. As I recall the outer edges of my rear wheels were spaced out further from the centerline of the chassis than the fronts. You can kind of see that in the picture below. In any event I'm not sure it really matters so long as everything is square with respect to the chassis. Equalizing the side-to-side rear track width will accomplish this.

Don't forget to set the car at the proper ride height when you make your adjustments. Also might need to account for any slope in your garage floor as well. With the car level and at the correct ride height, you can set the alignment independent of the weight on the chassis so long as you adjust it back up to the proper ride height when all is said and done.



48554

[Porky]

Great advice Karlos. I did what you advised and now I have the centerline of the car snapped on my garage floor. It's my wife's birthday tonight so it's going to be hard to get much more done. I'll let you know how I do when I get there.

Thanks