A hard hit can crack the teeth on the pitman shaft. The best check for this is to have the
"It is also interesting that the Cup guys generally want a bigger valve," he adds. "That's because they are usually running the bigger, higher-speed tracks and want all the feel they can get. They want to be able to tell whenever they dive off into the corner where the front end of the car is. But because they've got so much caster split in them now, the car will basically turn itself. That kind of gives them a false sense of feel, so you put a stiffer valve in it, and that way when they go into a corner, they can still feel where the car is."
The second variable in a gearbox is the ratio. The standard Saginaw gearbox produced by Delphi is available with several different ratios. They are 12:1, 14:1, 16:1, 17.5:1, and 20:1. The ratios are for the input shaft versus the output shaft. For example, a 12:1 gearbox would require 12 turns of the steering wheel to make the output shaft, or pitman shaft, make one complete revolution. Of course, you are never going to turn the steering wheel 12 times or want the pitman shaft to make a complete revolution, but this gives you a good idea of the steering rates. Generally, faster rates are used on tighter tracks while the slower rates are used at bigger tracks where less steering input is necessary. The 17.5:1 and 20:1 ratios are normally only used at monster tracks like Daytona and Talladega.
Still, even if you are racing each week on a tiny bullring, you may not want to depend entirely on a 12:1 ratio because it is the fastest. "We are noticing a trend of weekend racers on the shorter tracks going from a 12:1 to a 14:1 ratio," McBride says. "They don't race as much as the Nextel Cup drivers do, and they sometimes get a case of happy hands, or jerky in their reactions. The 14:1 ratio slows down the car for them. It keeps them from jerking the car around too much and makes it more driveable for them."
The pitman arm on the left is good, and the one on the right has been damaged in a wreck.
Your steering linkages need to be set up so that the gearbox is centered when the wheels are pointed straight ahead. That sounds like common sense, but it is easy to miss. There are a few ways to determine the center in the steering box. First, there is a hard spot that the driver can feel when he turns the wheel. This can actually be distracting to a lot of drivers, and if this is the case with you, tell your box builder you want the hard spot reduced. The second way is to notice the large flat on the input shaft. When the box is properly mounted, that spot should be facing upward.
Finally, you can check it manually. With the box connected to the steering shaft, turn the steering wheel fully to the left. Now, turn the wheel back to the right. The second time the flat spot on the input shaft comes up (you should be able to see it behind the coupler), that's the center. This is true for every ratio except 17.5:1 and 20:1, in which case it is the third time around.
In some cases, drivers that don't like to feel the hard spot in the center of the steering box will have the toe on both front tires moved slightly to the right by a degree (the left-front will have less toe-out and the right-front will have slightly more than normal). Now when the steering wheel is straightened up, the gearbox is set so that the driver will not feel the hard spot unless he or she turns to the right. This doesn't cause a problem, except the valve is now cracked open a small amount. When this happens, fluid pressure is trying to push it closed while the driver is holding it open, and this causes the power steering pump to work harder. This translates to a small amount of horsepower. Again, the best solution if your driver dislikes the hard spot that marks the center of the gearbox is to ask the builder to reduce it.
CJR has developed this fixture to quickly check a pitman arm. If it has any malformation,
This view looks at the part of the gearbox facing the firewall. The flat on the input shaf
Jeff McBride checks a new gearbox on CJR's steering dyno. This ensures that the gearbox wo