LS1_78Bandit
03-03-2006, 06:35 PM
I was chatting with a co-worker about my suspension dilemmas and I mentioned the potential binding issues of the poly bushings.
He couldn't understand how you would put the necessary stresses on a bushing that would cause it to bind. He thought that you should be able to design the geometry so that would never happen, so was wondering if it was just something particular to the older vehicles not designed as well as modern vehicles.
I couldn't even begin to answer that for him. Can anyone enlighten us? What bushings (location, not type) are most prone to this and how does it happen? Is this also an issue on modern vehicles?
astroracer
03-03-2006, 08:08 PM
Binding is an issue on any suspension that moves in more then one direction at a time. Putting stress into a suspension bushing is easy. Think about what the suspension is actually doing when you are turning your car into a driveway with a steep approach angle. The suspension has to not only go up on the low side of the car but it also has to extend on the high side and then roll around ALL of the pivot points. And while it is doing this it has to control pinion angle to keep the u-joints from binding. It gets especially bad when geometry points are not optimized and the working planes of the suspension arms are fighting one another to rotate.
With everything being equal, a suspension wants to rotate freely around all of it's attachment points. This is possible if loose enough bushings (or pivots) are used but the suspension, while it is going up and down and rolling side to side, also has to control the rearend housing to prevent wheel hop, pinion angle changes, brake hop and dog tracking. This means the bushings HAVE to be good, otherwise the suspension will act like a grocery cart with a couple of bent casters.
Design wise, even today, it is near impossible to get a freely articulating suspension that controls the rear housing and doesn't bind. Drag race style 3 and 4 link suspensions are notorious for bind and a ladder bar suspension is worse then that. You can loosen the suspensions with poly bushings in place of heim ends but these suspensions just aren't intended to be driven on the street. A leaf spring suspension is about as close to "perfect" as you can get for a street driven suspension and this is a reason you see so many of them still being used in new cars and trucks.
Sorry about the long post but this doesn't even scratch the surface on this subject.
Mark