ISUZU-Torsion Bars Explained

Torsion Bars Explained

There still is a lot of misconception about the nature of torsion bars. Hopefully this will help clarify the nature and design of the torsion bar independent suspension setup. To begin with, the torsion bar, like the Leif and coil, is simply a spring. A piece of material which when distorted tries to return to its original position. Like the Leif and coil, the torsion bar can loose its memory [sag], or break. The torsion bar, like the conventional Leif or coil spring is at one end fastened to the frame so as not to move during operation. The other end of the torsion bar is fastened to a pivot [the control arm]. Now as force [weight]

is applied to the pivot end [control arm] it tries to move and take the torsion bar with it, the opposite end being fastened to the frame, can not move so the bar twists and then tries to return to its memory position. This being the point at which the pivot end [control arm] originated. With no applied force [weight], the torsion bar will keep its pivot end [control arm] at the position or angle in which it was originally set. As a constant applied force [set weight] acts upon the torsion bar the torsion bar is resisted from returning all the way back to it's memory or set position. The amount by which the torsion bar can not return to its memory [set] position becomes pre load. Pre load is solely controlled by the amount of force [weight] applied to the torsion bar.

To adjust the ride height of the vehicle by winding the adjuster bolt at the fixed [frame] end of the torsion bar does not add any more force [weight] to the pivot [control arm] end of the torsion bar, therefore the pre load is unaffected, hence ride quality and torsion bar life theoretically remain unchanged. Winding the torsion bar adjuster bolt is the same as installing blocks between the axle and Leif springs or a set of coil spacers; it simply moves the spring to a different position.

The reason the truck may ride a little stiffer is because of the new angle of the pivot [control arm]. As this angle [control arm to ground] becomes greater, the pivot [control arm] exerts less force on the torsion bar effectively reducing the pre load.

Other reasons for a harsh ride after winding the adjuster bolts is YOU WENT TOO FAR. This is when there is not enough room or no room between the control arm and upper bump stops, leaving no room for downwards travel of the control arm. When to replace your torsion bars with larger ones is if you have added substantial weight [winch, large bush bar, heavy bumper, heavier engine, etc.] or if you are looking for a firmer ride. The affected longevity of related components such as c.v. joints, ball joints, spindles, etc. will be the same weather the heavier torsion bars are used or the originals are adjusted, since these components are affected by the selected angle of the control arm. After a height adjustment is made either way, it is a good idea to have an alignment, but you will most times find that everything is still in spec.


Thanks to Al Davis for this detailed article!
Last updated on 10/23/2001 07:15 PM