deDion Torsion Bar Spline Count Method

The most critical point to understand for successful ride height adjustment is that the front and the rear of the bar have different spline counts.  Since the circumference of the bar is the same on each end, but divided by a different number of splines, the distance between each spline at each end of the bar is different.  So if you rotate the rear 10 splines and the front 10 splines – you have moved each end of the bar a different distance in its socket – or perhaps more correctly stated, you have moved each socket a different distance around the bar.  Since in this case, the rear socket won’t rotate, you will have to rotate the control arm around the bar the 2.5mm/spline to take up the difference.  This is what gives the fine resolution in ride height adjustment.  If you just rotate one end w/ the other fixed in its socket you can only attain a 3 cm (30mm) change in ride height – and this is a quite common mistake. 

The final ride height occurs when the car’s weight settles the car against the initial (unloaded) arm position.  When installing, wherever the arm sits relative to the car – there is zero load on the torsion bars.  Once the car settles, it imparts its fixed load for that corner, the spring (bar) twists from it’s no load angle and allows the car to settle at the # pounds / pounds/inch (or angle of rotation in this case) rate.  That becomes the new ride height for the car.  If you give the lower control arm a new zero load starting point (by rotating the bar and installing the control arm in a new start point), it settles the same amount to a new end point (ride height).  All we are doing is finding the correct new starting point.

  1. After everything has been disconnected (specifically any shocks, sway bars or anything else that will restrict the free movement of the car and suspension) the bar is now ready to go in for the first time – with the car on the lift – rotate torsion bar until both ends will go into their sockets with the control arm sitting just a little below level (steps 12 & 13).  See picture 16.  You don’t have to drive the bar home yet; the splines should start by hand enough to give you the idea.  Don’t obsess about this initial position, it is just a start to give you a reference for the final adjustment – close is good enough. Once you think all is aligned close enough, then set the bar in place and attach lower arm to car. Steps 14 & 15.
  2. Now proceed to step 16 – attach enough of the arms to hold the car up off the ground.
  3. Now proceed to step 17 – on both ends, both sides of the car, for your initial reference, mark a spline on the bar and its mating spline in the socket.  Set the car down, roll back and forth, and bounce it a few times to settle ride height.
  4. Measure the distance from ground to some fixed reference point on the car (both sides – then comparing to the rear ride height). Determine the distance each front corner must move up or down to attain the desired ride height.
    1. By simple addition or subtraction, calculate the distance each side needs to move up or down.   If you do not have a reference to level the arms to,  perhaps you can raise (jack) or lower the car (sit on the corner) until the ride height is correct or arm is level, and then measure the amount of lift (positive or negative) you’ll need, i.e. the difference between the resting height and the new, desired height for that corner.
  5. Use step 18 and the chart to calculate the number of splines & direction the bar must turn on both ends. Mark the new target spline on each end of the bar.
    1. For example, say you have to raise one side of the car 25mm – count 10 splines in the correct direction from the old reference spline on each end of the bar (25mm/2.5mm/spline = 10 splines) and mark the new spline.
  6. Remove the bar, rotate until the new spline goes to the rear socket mark, slide in end.  You will have to rotate (raise or lower) the lower control arm until the new spline slides in at the socket reference.  That should give you the 25mm change you need. 
  7. Reattach enough arms (step 16), lower the car, bounce, roll, and check new ride heights.  You should be either very close or right on. If it needs it again, do it again.  Believe me, the more you do it, the faster you will get. re-connect everything once the front end is set. 

For final ride height target – rule of thumb – under load, i.e. w/ the car on all four wheels, sitting on the ground, the front ride height should be slightly less than the rears.  If the arm ends are a little high (car is lower) or a little low (car is higher) is not super critical.   Although lower is better – for this stage, a mm or 2 is not hugely critical. Should be a piece of cake. 

Good luck.