Rear upper control arm length for lowers A-bodies

[boss_hoss]

I’m chasing rear end vibrations on my 69 tempest and I’m down to either an unbalanced drive shaft or improper pinion angle. Im running adjustable rear upper control arms so I can adjust pinion angle for the lowered suspension but need help getting them in the general neighborhood with regard to length. For those of you run rear adjustable upper control arms on GM A bodies that have been lowered roughly 2 inches, what’s length do you have your control arms set at.

thanks
hoss

[Hotwire]

Hey Hoss,

You can't go by what others are doing, you have to set your pinion angle that's specific to your car. If someone has a different eng/trans combo it will alter their settings vs yours.

Don't guess at this as like you said, you'll be chasing your rear.

Follow this write up on calculating your working angle, it helped me in getting my car setup properly:

https://shiftsst.com/blog/post/driveline-angles.html#:~:text=Ideally%2C%20both%20driveshaft %2Doperating%20angles,life%20and%20could%20create% 20vibration.&text=When%20you're%20changing%20a,to%20maintain%20 this%20factory%20angle.

I used this digital angle finder when I worked my pinion angle, has a built in magnet, worked pretty well:
https://www.homedepot.com/p/Johnson-2-Button-Magnetic-Digital-Angle-Locator-1886-0000/204513508

Put the front a-arms on jackstands and put the rear tires on ramps. I usually jack the car up, rotate the pinion so it's parallel to the ground, and put the ramps sideways so the tires have positive stops front and rear and have no fear of the car moving while under it. This allows you to check the pinion angle with weight fully on the rear and no mechanical force affecting the rear.

One other thing, while you have the rear jacked up, fire the car up, put it in drive, and watch your pinion flange, driveshaft, slip yoke for ANY type of lateral movement. Should be 0 detectable movement while spinning. This will tell you your driveshaft, u-joints, yoke, etc are not bent or damaged. Just please, make sure you have the front end fully secure before doing this. I'd found my slip yoke was twisted, was going crazy trying to find the shimmy..

Hope this helps!