Alignments Questions

[01Y87]

I had my alignment checked today, and it seems the toe was off. But the rear thrust angle was not within specs either - and they tell me that you cannot adjust the rear thrust angle on a solid-axle car. is this true? How do you deal with a rear that is out of spec?

According to the GM manual, rear thrust angle (reference only) range is -0.25 to +0.25; mine is +0.48. Why does it say "reference only"? Mine seems quite a bit off! Can this cause tire wear? The other spec, "Sum Toe", reads -0.01 while GM says -0.3 to +0.3 with 0.00 preferred so mine is good.

My front toe spec was -0.09 (left) and +0.32 (right), total toe was +0.23. That right side was quite a bit off.

the new tires ride real nice!

[Injuneer]

You can adjust the rear thrust angle by using "adjustable" lower control arms (LCA's). Thay allows you to alter the length of one LCA or both sides to bring the axle back into being perpendicular to the longitudinal axis of the vehicle. The LCA's are a popular replacement item for anyone interested in improved handling or straight line traction. The adjustable feature is usually not required, but can be useful for adjusting the thrust angle, or for relocating the rear axle assembly in the wheel wells for clearance with large slicks.

I have the Spohn adjustable LCA's:

http://www.spohn.net/product.cfm?productid=1294

[01Y87]

Some places advertise a more expensive "thrust angle alignment"...is that a waste of money on these cars? Can you adjust the angle by using shims? What would cause the rear to be out like that, and how does that effect the wear or the ride?

[Injuneer]

There's no way to adjust the thrust angle, other than the way I explained. There is no way to shim the lower control arms.