Control Arms and AWD

Christena writes...
On the topic of cars, here's a question I've been curious about. I broke a control arm on the front driver's side or my car (a 96 audi A4, quattro). What is that? People mention the bearings, and make very sad noises when I say it's an all wheel drive. What does that have to do with anything?


Well Christina, I'm not familiar with the Audi Quattro but most cars have control arms in their suspension. Basically, a control arm is a bracket that pivots at both ends. Its purpose is to let two things, (say the body of the car and the wheels of the car) move in one axis (up and down) but not the other (side to side). From what I know, the most common problem with the control arm is the bushings at either end that wear out and have to be replaced. Sometimes, if you hit a major pot hole, the control arm will bend out of shape and the whole arm has to be replaced. When you say "people mention bearings" I would guess they are talking about bushings. Bearings are used on the axles and let the wheels spin around the axle with a minimal amount of wear. Of course, the '96 Audi A4 Quattro may have bearings in their control arms and their control arms may break so then I have no idea what is going on, which is standard operating procedure for me.


The reason that All-Wheel Drive makes a difference is that there are more parts and and a more complicated system. With the old system of rear wheel drive, we ask the front wheels to steer while we ask one of the rear wheels to drive. A very simple system. With front wheel drive, we are asking the front wheels to steer and one of those same wheels to drive. That becomes more complicated in the front end but simpler in the rear. When we move up to 4 wheel drive, we are asking one wheel in front to drive and one wheel in back to drive and both the front wheels to steer, but we have to decide when we need 4 wheel drive and when we need 2 wheel drive. Finally we have All-Wheel Drive, where we tell the car to figure it out by itself. If one wheel on either axle slips, the other is supposed to pick up the slack. If none are slipping, then we go back to the original one wheel to drive the car. In the mean time, the front wheels still have to steer. It is a great system, but it is very complicated. In a rear wheel drive you probably have direct access to the control arms and when you replace them, that is all you have to work on. With a modern all wheel drive, you may have the transmission, steering, or transfer case or any number of adjoining parts added to the equation. It would be akin to changing your underwear. If you were wearing a skirt, it may be a simple project. If you were wearing pants, it could get more complicated. If you have all wheel drive, you may be wearing pants, two pairs of socks, a snowsuit, hiking boots and snow shoes, AND you may have to take your pants off over your head before you can change your underwear, and that can get VERY complicated.