MECHANICAL DANGERS: PRODUCT DESIGN & VEHICLE MAINTENENCE
by John Lee
If you can't control yourself, how can you control the car? --James Besmer, Chief Instructor, Jim Russell British School of Motor Racing
In the first crash mentioned above, the woman stated that when she applied her brakes in the corner, her car unexpectedly turned hard to the right, forcing her off the road. It is unknown what exactly caused this sudden, strange behavior of her car, especially since her memory was so punchy. Perhaps she simply missed her "apex" (the inner-most part of a corner) and dropped her wheels off the edge of the darkened road, losing control when driving back on the pavement (power steering can prevent the steering wheel from being jerked out of one's grip).
However, this is also a symptom of worn out or broken "ball joints" in the front suspension. When the ball joints are loose, any hard braking or steering causes the "castor" angle of the suspension to suddenly change. A car can literally change lanes under braking, moving ten feet sideways, even if the driver holds the steering wheel perfectly straight. Oftentimes, a repair shop will not be able to diagnose this problem, which only shows up under medium to hard braking or lock-to-lock steering.
Ball joints can wear out after only 50,000 miles on some cars. Some vehicle manufacturers don't seem to build their ball joints hefty enough (a possible product legal liability?). The easiest symptom to notice is a "popping" sound coming from the front suspension when parking. The steering may suddenly feel extremely heavy or very light. Later, this symptom suddenly disappears. However, power steering tends to cover up these symptoms. Extreme tire wear, such as a new tire being destroyed in only thirty days, is the most obvious of symptoms, but most times this will not occur, and tire wear remains nominal.
Vehicle manufacturers aggrevate this problem by building suspension systems that overstress the ball joints, such as when a car hits a pothole or is lifted up on a jack for repairs. This causes the suspension to droop down, beyond its normal position. Suddenly, the ball joints are being bent and stretched by the powerful springs pushing the wheels down. On race cars, this problem is prevented by adjusting the shock absorber length to restrict how far the spring droops, eliminating binding and stress on the ball joints. One benefit to manufacturers of weak ball joints is reduced costs and increased profits.
I have personally had this problem happen to me, on two different cars, one European and one American. The symptoms I experienced are described above (but without the tire wear problem). Fortunately, I survived a near head-on crash, when my car suddenly changed lanes under braking, without me even turning the steering wheel. A repair shop was unable to diagnose my problem, so I quickly traded the car for a new one (passing the problem on to the next unsuspecting owner). Later, as I gained hands-on experience in race car maintenence and suspension alignment, I realized what had been the cause of my problem.
Whether or not a driver's vehicle steers in a straight line is important not only for obvious safety reasons, but also for reasons of defense from allegations of DWI. If the vehicle pulls to the right or left whenever the driver focuses on something besides the lines on the road, police might take an interest. However, having a vehicle freshly-aligned is not enough to ensure that it can drive straight.
The set up platform, that the vehicle sits on while it is being measured and adjusted, is perfectly level. However, in the real world, 99 percent of road surfaces are tilted to the right, to allow for rainwater runoff. This means that a newly-aligned vehicle still may not steer straight. As it goes down the road, the tires are being scrubbed sideways, due to the driver having to turn the steering wheel a tiny bit to maintain a straight line. Over time, this can wear the tire tread in such a way that the vehicle pulls more and more to the side. The problem is not alignment, it's torque ????????. Rotating the front tires to the rear can usually eliminate this problem, improving the steering. Rotating the front tires only, by reversing the right with the left, can sometimes perfect the steering, provided they have not been left on too long. This is something the driver can fine tune by simply paying attention to what his car is telling him.
Many luxury car makers require that their mechanics align a customer's car with a person sitting in the driver's seat, since this is the way the car is driven the majority of the time, without passengers. All race cars are adjusted this way. This can affect the adjustment significantly on many cars. Otherwise, the new adjustment doesn't seem to work once the customer drives away. Anyone can ask a mechanic to align a car this way. Manufacturers traditionally do not allow mechanics much leeway in correcting defects in a vehicle's inability to steer straight; usually only one adjustment is provided for, even though five or six parameters are perhaps at fault. It is cheaper and more profitable to build cars this way. Modification kits are available for car owners of many import-brand vehicles, which would allow a mechanic to fine-tune the wheel alignment for better steering and stability, and thus safety.
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