Mike S. Please read the below information and see if it makes sense to you.
"GM Torsion Bar 401
By Stephen Bradley (Dark Eternal)
To start out with, lets first discuss what a torsion bar is. A torsion bar is a type of spring, just like a coil spring or leaf spring. To be exact it is a type of rotary spring. A spring can be defined to be an elastic member which exerts a resisting force when its shape is changed due to an applied force and returns to its original shape when the force is let off. There are many different classes of springs, but I will only discuss a few that are relevant to us. The first is the most common, a linear spring. A linear spring requires the same amount of force all the way through its range of compression. The next class is a step linear. A step linear requires different forces at different positions of compression through the range, requiring more force the more you compress the spring but in steps. This means it might be easy to compress for half of the compression range and then very hard for the second half. The last class is the progressive spring. It is similar to the step linear but instead of being in steps and having a set number of different amounts of force required to compress the spring, it is progressive. This means that every little amount you compress the spring its gets harder. There are no steps, but instead it is a constant rate at which the force needed to compress the spring increases.
To define how a torsion bar works we can compare it to other springs. A coil spring uses compression and extension and depending on the design of the spring can be a linear, step linear, or a progressive rate spring. A leaf spring uses flex and is a progressive spring. The torsion bar on the other hand uses resistance to torque and is a linear spring. A torsion bar is essentially a steel bar with some form of splines on each end. On our GM torsion bars it’s not the type of splines you are used to, like what you would find on an axle shaft, but instead a hexagonal head, similar to a bolt head. In fact you can slide a socket over it if you have a big enough one. Now when one side is fixed to an immovable object and the other is twisted, torque is applied. The torsion bar resists this torque and like any other spring it returns to its original position when the torque is let off. Now let’s apply this to our trucks. The immovable object is going to be our frame, or rather the torsion bar cross member on our frame where the torsion bars are anchored. The other end is connected to the lower control arm (LCA). The LCA pivots on a fixed point on the frame and creates twisting motion on the torsion bar – the torque needed to make it a spring. For example, when the vehicles front suspension compresses, the LCAs move upwards and exert force onto the torsion bars, so they push back onto the LCAs, just like a coil or leaf would.
Now that you have a basic idea of how a torsion bar works lets discuss why it is what GM chose for our 4wd suspension. One answer is that it is cheap and maintenance free. Some torsion bars do use bushings that need greasing on other vehicles but GMs do not. Second, they are out of the way. A leaf spring can’t be used on IFS and a coil is in the way of the half shaft used to transmit power to your wheel in the front. The torsion bar is totally out of the way. Finally, it is adjustable. The fixed end of the torsion bar that is anchored in the torsion bar cross member is anchored into a “key” which can be turned with an adjusting bolt, therefore effecting the resting position of the LCAs and the height of the front of your vehicle. Sounds like the perfect suspension doesn’t it? Not quite. The fact that torsion bars are a linear spring effect the ride quality in a negative manner. Luckily, with modern technology and the advanced design of independent front suspension (IFS) ride is still going to be far superior to that of a progressive leaf spring and a solid front axle. Also, you may notice that the LCA on the GM IFS seems to be resting on its upper bump stop. This is not only a bump stop, but what is called a progressive dampner. It compresses at a progressive rate, simulating a progressive rate spring, and letting the torsion bars achieve close to a progressive feel. Another con is as you increase the ride height by adjusting your keys, the ride gets worse. Now it’s a common misconception that there is more of a load on the bar and this is the cause. That is impossible since the LCA moves as well, so there is no more torsion on the bar than before, the spring rate does not actually change like many belive. The twisting action does not change the pre-load on the bar directly, so cranking your bars is just like adding a block in the rear or a coil spacer. It is simply changing the position of the spring. Just to clear things up, pre-load is the amount by which the torsion bar can't return to its original (unloaded) position due to be installed in the truck. The reason for the bad ride quality is instead a combination of things. First of all, when you adjust the height up, the angle between your LCA and the ground is increased which effectively does reduce your pre-load by reducing the leverage your LCAs have on your torsion bars. This negativly effects the ride by taking the torsion bars out of the preload range they were designed to work in. In combination with that, if you crank too far your UCAs have very little room left between them and the lower bump stops, reducing downward travel. You also pull the LCA away from the progressive dampner, making it ineffective and putting yourself back into the position of having a linear spring. These are the reasons the ride gets worse! One last disadvantage is that like all other springs, torsion bars will wear out over time causing your front end to sag. The more weight on the front of your vehicle, the faster they will wear. Also, the more your suspension travels the faster they wear."
http://www.gmfullsize.com/tech/torsion401.html
"How it all works
Torsion Bars
A lot of the same principles used in coil sprung suspensions are transferable to torsion bar sprung suspensions. For this reason I will not go too in depth into the explanation of how tbars work.
"Cranking" the torsion bars involves rotating the anchor point of the tbars to provide lift to the truck. Fundamentally, this is the same as using a spacer in a coil suspension. Just like a spacer in a coil spring, cranking the tbars does not add preload, nor does it raise the spring rate. Remember, the only practical way to add preload is to add weight to the truck and the only way to change the spring rate is by changing the geometric and material properties of the tbar.
Since cranking the tbars does not change the spring rate, why do people say cranking the tbars makes the ride stiff? Well, the perceived stiff ride comes from the change in angles of the control arms, just like the coil sprung suspension.
Summary
- Spacers do not change the spring rate
- Spacers do not add preload
- Spacers by themselves do not make the suspension stiffer, the geometry of the suspension does.
- Cranking the torsion bars does not change the spring rate
- Cranking the torsion bars does not increase preload.
This was a very basic look at how certain suspension systems work and how modifications can change the way the truck feels. Hopefully some of the common misconceptions floating around the internet were clarified.
Having said all this, there IS a way to increase the preload without adding weight. A coil spacer long enough or the torsion bars cranked enough to completely extend the suspension all the way to the bumpstops will start to increase the preload on the spring. Of course, this means the one would be riding around on the bumpstops all the time and that would make for a very rough ride.
Lastly, I would like to thank a few people for their help:
Chris (Pismoboy) BSME, Frank (elripster) BSME (pending), and Geoff (AdmDrayton) PhDMate (pending) for their technical advice on this subject. Bob (Bob_98SR5) MABus and Tom (mertzer) BSChem for their proof reading."
http://www.robinhood4x4.com/suspension2.htm
SORRY MIKE S. these are mechanical engineers and automotive suspension engineers above.
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