Body Alignment to Rear Wheels/IRS

[mlewis]

All,

Continue to work on the body alignment and initial panel fitment.

I have the body now positioned back to front and centered (to the frame) side-to-side.

My dilemma is that I now noticed my rear wheels (IRS) are not evenly spaced from the frame (off 3/4" out farther on the DS than the PS) which then positions the rear wheels uneven to the body (PS in DS - out).

I have seen some threads on IRS offset. Is this amount of offset normal ?

If so any suggestions on how to adjust (wheel spacer ?)

Any/all advice is greatly appreciated.

[edwardb]

Sounds like you're confusing driveline offset with "IRS offset." The engine/trans/driveshaft are offset to the RH side in the chassis. But the IRS setup is symmetrical. Everything back there is the same side-to-side. Have you done your alignment yet? Would be easy to think something's off if you haven't done the rear alignment. Specifically the camber.

[Jeff Kleiner]

Paul beat me to it (but I’m sure he meant camber and not caster). Get the alignment done.

Cheers,
Jeff

[edwardb]

Paul beat me to it (but I’m sure he meant camber and not caster). Get the alignment done.

Cheers,
Jeff

I did... fixed it. :rolleyes: Thanks.

[mlewis]

Thanks both.

Sorry for the terminology mix. I am aware if the differential offset, but meant the hubs.

No alignment yet. I do have it up on stands and did a rough “alignment”. I measured from the frame to the center hub. Do you think the camber could be off that much and will pull/push each side that much to even it off?

So as long as my body is even to the frame, the rest should eventually line up?

Any quick tricks to double check?

Thanks again.

[edwardb]

No alignment yet. I do have it up on stands and did a rough “alignment”. I measured from the frame to the center hub. Do you think the camber could be off that much and will pull/push each side that much to even it off?

So as long as my body is even to the frame, the rest should eventually line up?

Yes and yes. Align the body to the same fixed point on the frame on each side. Camber (see, I got it right that time...) is only -0.5 to -0.75 degrees. But doesn't have to be off much to move an inch or more at the top of the tire at the body when corrected.

[mlewis]

Thanks Paul.

I definitely get that the top of the tire could be off based on alignment (and it was), I wasn’t expecting the center hub to be off so much. I’ll be patient and assume this will sort out with alignment.

The body alignment and fitment is turning out to be a lot hard than I anticipated.

[CraigS]

You can do a quick check w/ a carpenter's square and piece of straight wood trim. Notice I did not say a quick alignment. For this all that needs to be done is to make sure both sides are similar. Put the wheels on, drop the car off stands, roll it back and forth a little while also bouncing it. Use your square to adjust the rear tires so they are both at 90 deg to the floor. Now you are at zero deg camber. Hold one end of your wood trim against the outside surfaces of the rear tire about 13 inches off the floor w/ the length going toward the front of the car. I usually find a box or something to set on the floor so the top of the box is about the same height as the middle of the frame tube so I can let the trim piece sit on the box. Have your helper use a tape measure to check the distance from the edge of your trim to the outer surface of the main 4 inch frame tube just behind the front tire. Adjust the rear toe so both sides are the same distance from the frame. You can eyeball the wood trim to make it roughly parallel to the main frame but don't worry about making it perfect. At this point you know the camber is about zero on both sides. You also know the toe is equal on both sides but you don't know what it actually is. This is good enough to see how your tires compare to the body.

[rich grsc]

You can do a quick check w/ a carpenter's square and piece of straight wood trim. Notice I did not say a quick alignment. For this all that needs to be done is to make sure both sides are similar. Put the wheels on, drop the car off stands, roll it back and forth a little while also bouncing it. Use your square to adjust the rear tires so they are both at 90 deg to the floor. Now you are at zero deg camber. Hold one end of your wood trim against the outside surfaces of the rear tire about 13 inches off the floor w/ the length going toward the front of the car. I usually find a box or something to set on the floor so the top of the box is about the same height as the middle of the frame tube so I can let the trim piece sit on the box. Have your helper use a tape measure to check the distance from the edge of your trim to the outer surface of the main 4 inch frame tube just behind the front tire. Adjust the rear toe so both sides are the same distance from the frame. You can eyeball the wood trim to make it roughly parallel to the main frame but don't worry about making it perfect. At this point you know the camber is about zero on both sides. You also know the toe is equal on both sides but you don't know what it actually is. This is good enough to see how your tires compare to the body.
He is talking about track width on the rear IRS.

Make sure the IRS arms adjusted to give the same distance from the frame.

[mlewis]

Thanks both. I used a laser level to align to the frame and front tires. I did this while Tires off and still on the jack stands. I can redo after dropping to the ground.

I believe the arms are adjusted to be the same roughly. I also have the shock height adjusted to be the same. I did notice that the PS caliber is closer to the shock that the DS, normal ?

I will get it back on the ground later this week and see if it lines up to the body.

[CraigS]

Yes, but you are thinking of the old IRS. The 2015 IRS LCA is fixed length. So if camber and toe are equal on both sides, the track will be also