I plan on lowering the car in the near future, and I’ll be changing the rear LCAs and 3rd link. I know that with the stock configuration, the LCA are set horizontal with the ground. BUT,…if I lower the car and change the pinion angle, I’m not sure how much of a problem, if any, I could expect with non-adjustable LCAs. If I go with an adjustable 3rd link, is it necessary to install adjustable LCA, or will the non-adjustable LCAs be ok? Thanks.

 

You only need either an adjustable UCA (3rd link) or adjustable LCAs to set the pinion angle. If you use adjustable LCAs then you can also adjust the angle of the rear axle to the frame to make it perpendicular if required.

Here is a good link if you have not already seen it http://www.cherod.com/mustang/HowTo/LCA%20_adj.htm

 

PINION ANGLE

DRIVELINE ANGLE MEASURMENT

 

Actually, the stock LCAs are inclined slightly 'downhill' from the axle to the chassis (unfortunately, I don't remember how much off the top of my head, and that information is on another computer that I won't get to until Monday). What lowering does is make this inclination a little more severe and increases the amount of axle steer (the axle actually steers slightly as the car rolls). The effect of greater axle steer in this case is to increase vehicle understeer slightly. At some amount of lowering, which will vary among individuals and specific car usage, you begin to benefit from LCA (axle side) relocating brackets. The possibility of the relo brackets not getting installed in "perfect" position (or the brackets themselves being slightly "off" - everything man-made is subject to tolerance) is a pretty good reason to choose adjustable LCAs so that you have the ability to properly square the axle in the chassis.

Welcome back.


Norm

 

adjustable lca's come in handy depending on track and configuration......

 

I've thought of getting one of the suspension design programs that will calculate the center of gravity, roll center, instant center, etc. as a result of suspension changes but I don't want to spend a day crawling around under the car trying to take measurements.

Are the stock S197 numbers available in the public domain somewhere?

 

I haven't seen S197 coordinates posted anywhere, and I've only taken a few of my own (they might be good to about ±1/16"). I got about 3/8" difference in the Z-coordinates (vertical) of the rear LCA pivots.

Handling-wise from running the numbers through a little spreadsheet, there appears to be enough change in the axle steer from only 1" of lowering for at least some drivers to notice. I was surprised by the difference, but having seen it - and assuming that the Shelby axle uses the same OE LCA brackets as the GT - I think it is enough and in the right direction to explain Sam Strano's observation that the GT slaloms better (at auto-X) than the Shelby even though the Shelby is better overall on most course layouts. Attempting to make the Shelby match the GT at slalom would kick the Shelby out of F Stock for sure, and probably all the way to
C Prepared if corrected fully.


Norm

 

So what would have to be done to 'correct it fully'?

 

Relocate the axle side pivot point elevation using essentially the relo-bracket approach but not necessarily the hole locations of commercially available pieces. Maybe change the lateral locations of either axle or chassis side pivots to affect the rate at which the axle steer varies with ride height.

Perhaps "corrected fully" is misleading - if you're tinkering in CP, you're probably tinkering with this stuff with an eye toward making it suit you. For example, correcting axle steer to zero at static ride height could end up being too loose to consistently drive quickly.


Norm