Control Arm Conundrums
 

Hey I got 2008 GT Vent and am wanting to install a one piece drive shaft.

I'm lowered about 1" front and 1.25" in rear with steeda springs, koni's, FRPP sway bars.

I plan on replacing either UCA or LCA's and maybe both to adjust out the pinion angle.

My question is if replacing both should I go with an adjustable UCA and non-adjustable LCA's or non-adjustable UCA and adjustable LCA's?

I want very little to no increase in NVH so poly bushings all around.

The adjustable LCA's seem like the easy choice because the are easy to adjust, but likely this will be a set it and forget it deal for me so the UCA being harder to adjust is probably ok.

Both being adjustable seems overkill. So which control arm is better to have adjustable or is it really just preference?

I cast my vote for an adjustable upper only.

Adjustable upper only. This makes setting the pinion angle easier because you only have 1 arm to adjust. Going back and forth on the adjustable LCA's would be a total pain, and more difficult to get it just right.

I'd go with adjustable LCAs. Aside from being easier to get at (to periodically lube), you can also adjust thrust angle with LCAs. Can't do that with an adjustable UCA, and if you ever get relo brackets you might find it necessary to do so.


UMI, Spohn, and Currie all make LCAs with poly bushings at one end and not-all-metallic spherical joints at the other (Roto-joints, Del-spheres, and Johnny Joints, respectively). I've had the Curries on my '08 since July of 2012, and the only reason I've had to lube them has been to eliminate a little "stiction" (something that ALL polyurethane bushings have) and to make sure that the Johnny Joints also remain free-pivoting.




Norm

Norm has some good points. Going with adj. LCA's allows you to adjust thrust angle and they are easier to get to. In my current setup I have to remove the UCA from the car to properly torque the backing nuts once the length is set correctly based on the pinion angle. You are correct in assuming it's a set and forget thing though. Using loctite (red) and the proper torque, over the few years I've had the UCA and at least 15k miles or so, I've never once had to tighten or re-adjust it EXCEPT when I went lower with my springs. Every time I've taken it off the car I've checked it and it's so tight I have to put it in a vice to adjust it. That being said you have to weight the benefits/detriments. If you go adj. LCA then you will have to take them off as a pair and sync the lengths before re-installing when you want to adjust them because if they are off then the rear end isn't properly aligned and the rear of the car will track to the left or right.

As for you wanting to go all poly bushing. I have to recommend against this. The rubber bushing on the stock control arms allow for some flex. When you go all poly you reduce the amount of flex the bushings allow and induce bind in the rear end. This will prevent the suspension from traveling as it should. If you go poly on the car side and spherical on the rear end side of the control arms then you effectively eliminate any bind caused by the bushings and your rear suspension will travel more easily and perform better.

I would recommend solid lowers and an adjustable upper. In fact, I'd recommend the improved geometry of the longer 2011+ UCA & Mount. It is a direct swap to your 2008 if you buy both pieces. This will improve handling & grip, and allow you to adjust pinion angle.