Four things you need to know before buying a steering gear that fits the vehicle:
1. As said, it's the torsion bar that controls the steering "feel", not the gear ratio
2. The gear ratio controls the amount of steering wheel motion needed for a given turn, and in general, most old domestic cars have WAY too much steering wheel motion/high numerical gear ratio. There are exceptions.
3. Pump pressure controls the amount of steering "assist"; in combination with the torsion bar stiffness. GM has even gone so far as to produce variable-pressure devices (EVO--Electronically Variable Orifice) that allow high-pressure at idle and low speed, and reduced pressure at highway speed. In terms of our older vehicles, GM increased the PS pressure sometime around 1971.
4. Different chassis designs require different STEERING STOPS. Older A-body famously has steering stops on the steering knuckle, which bang into reinforced sections of the lower control arm. There may be ~45 degrees of Pitman arm travel. F- and X-body--and others--have steering stops built into the steering gear. They may have ~30 degrees of Pitman arm travel. If you use an F- or X-body steering gear in an older A-body, it'll take forty acres to do a U-turn. I learned this the hard way. "Turns lock-to-lock" means NOTHING unless it's correlated with the degrees of Pitman arm motion. You can install a 2.5 turns lock-to-lock steering gear into a vehicle that had a 4-turns steering gear, and gain NOTHING in steering quickness. You're very likely to lose steering angle, though. The difference may not be the gear ratio, it may be the steering stops. The 2.5 turns box is merely the same ratio as the 4 turns box, but with restrictions on how far the Pitman arm moves. It hits the stops sooner, which is the only reason it's got reduced lock-to-lock motion.
Bonus Info:
LOOK at the Rag Joint on the input end of the steering gear. If the metal "safety stops" are polished...the rag joint is DONE. The rubber/fabric disc deteriorates over time and with use, at some point they become overly flexible. Steering precision suffers and the steering wheel has to be perpetually sawed back-and-forth to keep the vehicle on course. Some vehicles are famous for wiping-out the rag joint (GMT400 trucks, for example) but any vehicle with a rag joint is a candidate for rag joint renewal, or replacement with a U-joint.
|