There are several disadvantages to traditional gearboxes: the box consists of many moving parts and there‘s quite a bit of friction with many wear points. This is one reason why the steering feels so sloppy on an old car. The internals of the box are just worn out. Compared to a rack and pinion system, a traditional steering box is quite complicated inside, and the system has more wear points compared to a rack and pinion. But despite these drawbacks, it’s a very good system that, with the right internal parts, can perform as good as if not better than a rack-and-pinion system.
This is a great time to replace your coupler (rag joint) if it’s worn out, which it most likely is. But, if it’s still in great shape, just reuse it, since the splines are the same as the new box.
How does a recirculating gearbox work?
The recirculating-ball steering box contains a worm gear, which is comprised of a block of metal with a threaded hole in it. This block has gear teeth cut into the outside, which engage a gear that moves the pitman arm back and forth. The steering wheel connects to a threaded rod, similar to a bolt, which sticks into a hole in the block. When the steering wheel spins, it turns this bolt. Instead of the rod twisting further into the block the way a regular bolt would, this rod is held fixed, so as 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 of the threads are filled with ball bearings that re-circulate through the gear as it turns and acts as rolling threads. The balls actually 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. Without the bearings in the steering gear the teeth would come out of contact with each other for a moment, making the steering wheel feel loose and floaty.
How does a rack-and-pinion system work?
The modern rack-and-pinion is actually a very simple system. A 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 the 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, which 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.