Knowledge is power in making the right choice in steering with understanding the steering system basics.
From the 1950s to the 1980s, the conventional recirculating ball steering gear was the dominant system. The 1980s saw the introduction of the front-wheel-drive passenger car with rack and pinion steering. This was due to packaging and not having to work around an oil pan with a drag link. Rack and pinion systems also weigh less and use fewer parts. The manufacturers were able to bring the cost of rack and pinion systems down due to increased automation in the final machining process. Today, most passenger cars and light trucks are equipped with rack and pinion steering. The designs of both systems are changing to used less hydraulic assist to reduce drag on the engine.
One of the main reasons for owning a Pro-Touring classic car over a stock or Pro Street vintage car is to be able to go fast around corners and curves in addition to straight-line performance. While much attention gets paid to fancy coil-over shocks and three-link suspensions, the steering system is often overlooked. With the growth of this build segment, the choices for our classic cars’ steering systems have never been so vast or so confusing. What ratio is best? Does it affect bump steer? Power or manual? Rack or box? The choices are endless.
Recirculating-Ball Steering Box
Today’s conventional steering gear is a rack and pinion gear in reverse. The difference is the friction reducing ball nut and screw that converts the rotation of the steering wheel into the longitudinal movement of a rack gear attached to the ball nut. The pinion is called the sector and is rotated by the rack. Most systems use a torsion bar and rotary valve to supply hydraulic pressure to the power piston that is part of the ball nut and screw assembly. Attached to the sector is the pitman arm. The pitman arm moves in an arc and is connected to a series of linkages. Independent front suspension passenger cars and light trucks use a power assist steering gear, idler arm, center link and tie rods to connect the steering gear to the steering knuckle. The pitman arm and the idler arms are fixed to move in a lateral plane. The pitman and idler arm are connected to the center link with fixed joints. This allows the center link to move in a lateral plane. The center link moves the tie rods to steer the vehicle. The tie rods are attached the center link and steering knuckle with ball and socket joints. This makes a total of four ball and socket joints and four fixed joints.
How does a recirculating gearbox work? The recirculating-ball steering box contains a worm gear. You can imagine the gear in two sections. The first section is a block of metal with a threaded hole in it. This block has gear teeth cut into the outside of it that engage a gear that moves the pitman arm back and forth. The steering wheel connects to a threaded rod, like a bolt, which sticks into a hole in the block, and when the steering wheel spins, it turns this bolt. Instead of the rod twisting farther into the block the way a regular bolt would, this rod is held fixed so that when it spins it moves the block, which moves the gear that turns the wheels. Rather than have the bolt directly engage the threads in the block, all the threads are filled with ball bearings that recirculate through the gear as it turns and acts as rolling threads. The balls serve two purposes. First, they reduce friction and wear in the gear, and second, they reduce play in the gear. If it were not for this ball bearing design, slop would be felt whenever you changed the direction of the steering wheel. This is because without the bearings in the steering gear, the teeth would come out of contact with each other for a moment, making the steering feel loose and floaty.
Steering gearboxes are set up with different ratios that affect how many times you must turn the steering wheel to get the front wheels to turn lock-to-lock. For example, in a wide-ratio box you may have to turn the steering wheel 4.5 revolutions to get the front wheels to turn lock-to-lock. For a close-ratio steering box with a ratio of 12.7:1 it will only take 3 revolutions of the steering wheel to go lock-to-lock. So, what difference does 1.5 revolutions make? The answer is a lot. You may not notice it that much driving to the grocery store, but on a road or autocross track where you’re constantly throwing your car back and forth through the turns, the wide-ratio box makes you work much harder than the close-ratio box. More work will tire you out sooner and affect your performance. The close-ratio box will also make your car feel more responsive since it will require less driver input to cause your car to maneuver.
In addition to the ratio steering, gearboxes can also be adjusted for effort, or resistance, you feel when turning the steering wheel. In a car set up with low or no effort, you will have truly little feedback through your steering wheel and the car will feel like it is floating around on the road. You need to find a happy medium between low effort when you are moving slow or sitting still and a higher effort setup that would be good at speed. Keep in mind that the diameter of the steering wheel also affects this ratio, or at least how it is perceived. A smaller wheel will make the ratio seem even quicker, so a small wheel coupled with a fast 12.7:1 steering box might not be the best choice.
There are several advantages to recirculating-ball systems. First, by varying pitman arm length you can easily offer steering travel than a rack-and-pinion system. Second, it is typically less expensive than converting to a rack-and-pinion system, perfect for someone on a budget. This time-tested steering system is very rugged, and it is still preferred in racing organizations like NASCAR. Third, this is a very easy-to-install upgrade to your car and is generally a bolt-in deal that will keep your car with a factory look.
There are also several disadvantages to traditional gear boxes. First, since the box consists of many moving parts, there is quite a bit of friction and many wear points. The design also makes it less efficient than a rack-and-pinion system and it requires more effort. You also need to consider that a gearbox steering system has quite a few more linkage wear points including the inner and outer tie rods, the pitman arm, and the idler arm. Lastly would be weight, even when using the lighter gearbox, the recirculating gearbox-based steering system is quite a bit heavier than the more compact rack-and-pinion system.
Conventional Steering Gear Inspection
The best way to inspect the steering system is with the vehicle on the ground or on the turn plates of an alignment rack. The inspection should begin with the pitman and idler arms. They should remain in the same plane as the wheels are turned from lock to lock. Some idler arms have a specified endplay that is measured with a spring tension gauge. Next is the steering gear. Check for leaks at the sector shaft. If these components are OK, check the play in the steering wheel. Both the worm and sector and recirculating ball gears have a thrust adjusting screw. A rule of thumb says that there should be one to two inches of free play in the steering wheel and no binding when the wheel is turned from full lock to lock.
The thrust adjusting screw is located above the sector. Adjusting the screw can change the amount of free play in the steering gear. It is important to follow the recommended adjustment procedures, as some gears cannot be adjusted in the vehicle. If a recirculating ball steering gear is worn or has an internal problem, the safest approach is to replace the steering box with a warranted remanufactured gear.
The disadvantage of a conventional steering gear system is its complexity and the points where play can stack up. Excluding the steering gear, there are seven isolated wear points that are sealed and lubricated. If each joint has 0.020” play, it will equal 0.140 inch. The combined tolerances of each joint stacks up, which is more than 1/8-inch play in the linkage.
Rack-and-Pinion Steering
A rack and pinion steering gear uses a pinion gear to convert the rotation of the steering wheel into the lateral movement of the rack gear. The tie rods are attached to the ends of the rack with a ball and socket and conventional tie rod end connected to the steering knuckle. This reduces the number of ball and joint connections to four. The hydraulic power assist piston is in the center of the rack with the tie rods attached using a threaded end to hold the ball and socket joint.
A variation of the rack and pinion steering gear is the center take off. The tie rods are attached to the center of the rack and the power assist cylinder is moved to the end of the rack.
The tie rods are designed with extended length to reduce the amount of bump and roll steer. The pinion gear is adjusted by a support that rides on the rack below the pinion gear. It has the same function as the thrust screw for a worm and sector or ball nut and sector. Most of the supports are preloaded with a spring. It is recommended to use the manufacturer’s adjustment procedure to ensure the proper preload on the rack.
A rack-and-pinion gearset is enclosed in a metal tube with each end of the rack protruding from the tube. The gearset accomplishes two things. First, it converts the rotational motion of the steering wheel into a linear motion needed to turn the front wheels, and secondly, the gearset provides gear reduction, which lessens the effort needed to turn the wheels. A rod called a tie rod connects to each end of the rack. The pinion gear is attached to the steering shaft. When you turn the steering wheel, the pinion gear spins, moving the rack. The tie rod at each end of the rack connects to the steering arm on the spindle. On a power system, part of the rack contains a cylinder with a piston in the middle and this piston is connected to the rack. There are two fluid ports on the rack: one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn moves the rack providing the power assist.
Advantages of the rack-and-pinion systems are many. First is its simplicity. With only two moving parts there is not only less friction, but the positive engagement of the system gives a very tight and responsive feel to the steering. Secondly, the complete system has only four wear points in the linkage: the inner ball joints and outer tie-rod ends. This simplicity and lower number of parts is one reason why most new cars use rack-and-pinion. Third, a rack-and-pinion system is quite a bit lighter than a traditional box system. Less weight off the front of the car is always a good thing to strive for. Fourth, because of its design you often gain added clearance for headers and the rack-and-pinion is sometimes easier to package into the car.
Every option in life has drawbacks and rack-and-pinion is no exception. Due to the limitations on the number of teeth that can be cut into the rack, there is typically less travel available compared to a recirculating-ball system. Another thing to consider is that a rack-and-pinion system will require quite a bit of work to retrofit into an older car. In some cases, you will have to notch the frame and relocate the sway bar. You will also have to calculate the geometry so that you do not end up with poor handling due to bump steer and a host of other issues. If you are buying an aftermarket front subframe you may have no choice but to go with a rack-and-pinion setup, especially if it was designed to accommodate it. Lastly, a rack-and-pinion system, especially in kit form, will make your wallet quite a bit lighter than tossing in a rebuilt close-ratio box.
Rack and Pinion Inspection
Some are manual, but most are power assist. Inspect the boots and pinion seal for leaks. If it is leaking or has an internal problem, the safest approach is to replace the gear with a new or remanufactured gear.
The tie rods are directly connected to the rack gear assembly. A ball joint connects the tie rod to the rack and a tire rod end, which is also a ball joint that attaches to the steering knuckle. These applications require a special tool to remove the ball joint from the rack without damaging a seal on the power cylinder. The center takes off steering gear uses rubber bushings to attach the tie rods to the center of the rack housing.
Power or Manual Steering
No matter what system you choose, you will need to decide whether you want it to be a manual or power-assisted system. Manual steering has long been popular with the drag racing and Pro Street crowd for one simple reason: weight. Getting 20 or 30 pounds off the front of the car is a big deal for a straight-line car and, besides, getting those front skinnies to turn does not take a ton of effort. By ditching the power steering you also gain a few horsepower since the engine no longer has to turn the pump. Again, the small gain is not worth the extra effort every time you have to turn the wheels. With a car that handles, those skinny front tires have now been replaced with wide swaths of rubber that have a significant footprint in contact with the asphalt. All this resistance, especially at low speeds, makes the weight savings of ditching the power steering not worth the hassles of living with the car. Could you do it? Sure. Should you do it? Not in our opinion. Besides, driving a car on a road course is tiring enough without the added effort needed to manhandle your steering wheel back and forth. Drivers of cars defined as Pro Touring or Resto-mod worry about weight too, but not at the detriment of overall driving performance.
Power-assisted steering systems have a high- and a low-pressure circuit. A power steering pump is turned by a drive belt and pressurizes the fluid going to the gearbox to somewhere between 1,200 and 1,600 psi. The low-pressure line sends fluid back to the power steering reservoir where it is pumped out and sent at high pressure back to the gearbox. It is especially important that you keep this in mind when choosing the lines for your system. The low-pressure side is pretty forgiving, but you want to make sure to use the right parts for the high-pressure line. Another good idea is to incorporate some sort of cooler for your power steering fluid. During track use, fluid temps can get well over 200 degrees, and this will affect the performance of your system. In fact, if you are using an older style pump where the reservoir tank is soldered to the pump body, this type of high heat has been known to cause the parts to separate, throwing fluid all over your hot engine bay and onto the track. Not good at all. Remote reservoirs are one way around this problem, or you could use a modern unit with an integrated non-soldered or plastic tank.
The Bottom Line
According to a representative at Unisteer, “In general, when considering the option of a steering box versus a rack-and-pinion, one must always remember that either system will only perform as well as it is designed and built for its particular application. A poorly designed steering box setup may not function as well as a rack-and-pinion setup, and vice versa.” You need to think about how you plan on using your car. If your car will never see the track, then you might not need to run a power steering cooler or must worry about using the older soldered pumps.
Whichever way you go, it is important that you ask the right questions of the various vendors and explain to them how you will be using your car. Through proper parts selection you will end up with a steering system that will make your ride much nicer to drive.
