At this stage, after having removed the torsion bars from your 944 as described in Part I, hold the torsion bar in your hand and take a good look at it. You will immediately notice the splinned ends. Take a closer look and you will notice that one end has more splines than the other. In fact the inner end has 40 splines and the outer has 44.
Now here comes the fundamental concept of the torsion bar adjustment (i.e. indexing). Nowing that a complete circle has 360 degrees imagine that each end of the torsion bar is actually 360 degrees divided by the respective number of splines. The inner end has 40 splines therefore each spline is seperated by 9 degrees (360 divided by 40) and the bar’s outer 44 splines are each seperated by 8 and 1/6th degrees(360/44) or 8 degrees and 10 minutes (remember your high school geometry? There are 60 minutes in a degree.).
Here comes the real `leap of faith. Let’s image you are at the driver’s side rear facing the spring plate. If we fix the outer spring plate on the outer end of the torsion bar and then move the torsion bar inner by one spline (in the CCW direction - moves the spring plate up and lowers the car), we will have changed the position of the spring plate (relative to the ground) by 9 degrees. Now if we fix the inner splines and now relocate the spring plate (in the opposite direction(CW) - moves the spring plate down raising the car) we will be essentialy removing 8 degrees 10 minutes from the 9 degrees we advanced on the inner splines, thus resulting in a NET 50 minute change in the spring plate position. Think about it, and reread this paragraph until you GET IT. Due to the 4 spline difference between the inner and outer splines of the torsion bar, adding then subracting these relative angles allow us to adjust the rride height to within fractions of an inch.
If you understand the meaning of the preceeding paragraph you are ready to index your own torsion bars. If you’re lost or confused at this point, get help. Your next question will probably be "but how much do I raise or lower the spring plate in order to get the ride height I’m looking for?". If you are not changing the torsion bars and you are starting from the factory torsion bar position(you did take notes when you took it apart didn’t you?), you can ‘estimate’ the ride height change(approx 6.5mm for a 50 minute change) by using basic priciples of geometry a the rules of the great queen SOH-CAH-TOA. If you are replacing the trosion bars with ones of different rates or did not note the location of the spring plate(dumb-dumb) before removing the torsion bar, the answer to this question, I’m sad tosay is: "Trial and error my friend, trial and error." When I bought my new torsion bars, and dared ask this ‘stupid’ question, the customer service rep at Automotion gave me that answer. I thought he was nuts! He also told me it would probably take three tries to get right. I whimpered then cried. My better half Kristine smacked on the head and snapped me back to reality. "Thanks Kris, I neede that".
Unfortunately, he and she is right. It will take about three tries and a good smack on the head(maybe more) to get the ride height right. This effort is aggravated by the fact that you must basically reasemble the entire rear torsion bar assembly, remount the wheels, then role the car along enough to settle the suspension before you can take the a valid ride height measurement. Once you take your measurement you then have to dissasemble the rear suspension once again to make any necessary corrections to the ride height. You repeat this process until you get it right. (Lord take me know!).
The 944 is a wonderfull car but the design of it’s rear torsion bar housing does not allow for easy adjustment. While I have no first hand exoerience with a 944 rear end coil-over setup, it would certainly be a great if you plan to change your rear ride height on a regular basis.
Hope this helps with your attempt at turning your 944 into the ultimate handling machine of your dreams.
Marc B. firstname.lastname@example.org