06-12-2012, 02:24 PM
Join Date: Jan 2007
My Ride: '03 330ci / '98 M3
| You can put a straight edge, flat side down, on the carrier and mark the angle of the trailing arm itself up against the the carrier pretty accurately that way (let the straight edge extent to overlap the side of the RTA and mark a line on it that you can reproduce when torquing it down with the new bushings). Do this with the car either on level ground (if you can get under there), or with the rear end on ramps. The ride height shouldn't change significantly between those 2 scenarios.
Though, I will say that from my experience with doing this on E36's a few times, if you're running limiters, the 80 ft-lb torque spec on that car isn't enough to completely keep the carrier from rotating around the bushing. It will shift over time with vibration, making this entire process completely moot, as it preloads itself in a short amount of time. Any quick deflections from suspension movement aren't enough to rotate it in real time though. So, IMO, even the 8mm rule will be enough to get it in the range that it will correct itself. I actually go harder than the 80 ft-lbs torque spec, so I can prevent mine from twisting.
Another way to do this is to make a tool. I bought an aluminum L-bar at the hardware store and cut it to size. I notched out part of the L on the ends and drilled holes to mount it to the carrier on one end, and to mount a small L-bracket on the other end with a bolt in it that goes into the center of the hub. I measured my ride height with the car on the ground. Then I pulled the wheel off and used a jack under the RTA to get it to the same position with the wheel off. I bolted the tool to the carrier and saw how far down the other end would have to go in order to have the bolt/stud be in the center of the hub. I took note of that measurement and drilled a hole in the small L bracket far enough down to offset it.
I'm probably not explaining it well, but I basically made this, but without the fixed reference point on the hub side...I marked my reference point based on my ride height:
The end that goes into the hub is offset a specific height from the carrier end. Just let your tool hang wherever it lies with the RTA jacked up to "ride height", and mark your small L bracket where the center of the hub is. Now you have your reference point to set the angle when you put it together. If i'm not explaining this well enough, I can take a picture of the tool I made. It would probably make more sense.
Last edited by fiveightandten; 06-12-2012 at 02:25 PM.