Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: How doe a traction bar work?
When we used to build hot rods with leaf springs, spring "wrap-up" was a common problem. What happens is that, as power is applied to the pinion gear, it is supposed to rotate the ring gear and turn the axels. When the tires resist that, the pinion will "walk up" the ring gear instead. In doing that the whole axel assembly will rotate, maybe as much as 15 degrees. In the process it bends the leaf spring into an "S" shape. When the tires break loose the springs snap the axel back into it's designed alignment. Then the tires grab hold and the whole process starts over. The result we used to call "axel hop."
We built two types of bars to remedy this condition. One was a link bar. There is an eye on a bracket welded or bolted beneath the spring plate, and another eye below the front spring eye. Then a rigid bar is linked between these two eyes. That effectively forms a parallelogram. The axel tube can now move up and down, but it can not rotate without stretching, compressing or bending something.
The other kind of bar we built was a rigid beam that bolts to the bottom of the spring plate. It extends forward to a point an inch or two below the front spring eye. When the axel tube starts to rotate, the front of the beam swings up. When a bumper on the top of the beam hits the spring eye, or a plate welded to the frame, it effectively stops the twisting.
Another way we discovered to reduce hop was to move one of the shock absorbers to the front of the axel tube, and now you see this on most pickups. What that does is make one shock compress and the other extend for the axel to rotate. It inhibits wind-up, but won't stop it completely.