Torsion Bar Re-Indexing PDF Print E-mail
Written by Joe Paluch   
Tuesday, 12 September 2006 16:14
What this procedure does is to calculate an effective stiffness of the rear suspension.

Then using the rule that torsion bar spring rate goes by the 4th power of the diameter it can calculated the relative increase in stiffness. Then careful measurements allow you to set the bar before you install it in the car. This way once it is the car it set to go and only minor adjustment of the spring plate is required to get it spot on perfect. No more adjust install in the only find it is hosed and do it again.

1) Remove or disconnect the rear swaybar.
2) Take measurements (on each side) from the torsion bar end cap to the ground with the car on the ground. It is easiest from the bottom of the cap to the ground. (See pic below)
3) Lift the car on one side just to the point that the rear tire comes off the ground.
4) Take a similar measurement as in #2
5) Do the same thing on the other side of the car. (These measurements should be the same on each side.)
6) Enter these values in the spreadsheet along with new and old bar diameter. Stock was 23.5 in most cases, but you can measure after you remove it. Then enter and ride height change you may want. The number you want is the total height change (delta H) number. (See Screen Shot).
9) Pull rear suspension as assembly (torsion bars and trailing arms together)
10) Set this assembly on level ground with bars unloaded. (See pic below)
11) Take the "H" measurement from the "banana bar to the hub" Straight line down. Record for use later. (see pics below)
12) Pull torsion bar out on one side of the car only.
13) Install new bar & Eye ball new "H" length for new bar
14) Measure new height "H"
15) Repeat steps 13 & 14 until proper height change as determined from the program is achieved.
16) Repeat steps 11 through 15 on the other side.
17) Reinstall rear suspension
18) Measure new ride height. (This value should be the same #2 plus or minus the ride height you wanted to change)
19) Use the spring plate to achieve any fine-tuning needed.
20) A proper alignment and corner balance is advisable to ensure everything is perfect
Here is Excel program you will need.

Excel Program File