Many enthusiasts have found that an easy way to upgrade the handling on a hot street muscle car is to convert to a Saginaw quick-ratio power-steering box by bolting in a replacement stock gearbox sourced from a local salvage yard.
These quick ratio gearboxes were original equipment on some mid-size models, and they can be transplanted into most other Chevy muscle cars. Not only will these gearboxes improve the steering and handling of your car with a more responsive lower gear ratio, but they will also reduce the steering wheel travel to less than three turns, lock to lock.
When searching for a replacement gearbox, remember that the more responsive 14.4:1 ratio gearboxes replaced the earlier 17.5:1 ratio boxes in most Chevrolet models by the 1973 model year.
A better choice for handling is the 12.7:1 ratio boxes found on some of the higher performance factory muscle cars from the 70s and 80s. The 1969-1976 Camaros, 1964-1976 Chevelles, Malibus and Monte Carlos used an optional quick ratio 12.7:1 unit. These gearboxes will interchange with the higher ratio gearboxes as an easy bolt-in performance conversion. 1982-1996 S10 pickups used a 14.0:1 ratio gearbox that will interchange into earlier vehicles, but requires some modifications which makes them a less desirable choice.
Gearboxes that were original equipment on 1983-1988 Monte Carlo, 1983-1984 Hurst Oldsmobile, 1985-1987 Olds 442, and 1984-’87 Buick Grand National, have 12.7:1 ratio units that can be identified by a “YA” marking on the end cap. These gearboxes will reduce steering wheel revolutions from lock to lock down to 2.25 to 2.75 turns.
Most of these gearboxes are the four-bolt mount but there are two different three-bolt mount gearboxes that were used as well. To keep things simple, all of the 1970 and later Chevelle, Camaro, Nova and Firebird have the same steering box bolt pattern so searching for these gearboxes eliminates any mounting problems. Aside from the mounting, all of these gearbox units are all interchangeable.
An important thing to remember when interchanging Saginaw gearboxes is to use your original pitman arm and idler arm if possible in order to maintain the proper steering geometry. Another thing to keep in mind when interchanging between earlier and later GM gearboxes–the power steering hose fittings are not the same. Later fittings are metric with an O-ring incorporated, where the earlier gearboxes use the standard inverted-flare fittings.
The good news is that most auto parts stores sell standard thread to metric thread adapters in several different sizes that allow you to use your original hoses with the later-design metric gearboxes.
Most builders recommend using the power steering pump that mates with the high performance steering box that you salvage. This way you are sure that the pump can keep up with the demands of the box.
The rag joint or steering gear coupler may also have to be changed. These can be obtained with the gearbox when being pulled from the donor car. New ones are still available from the GM dealerships as well. The coupler off a 1977-and-up Chevy pickup (GM part #7826542) works to adapt the early-style steering shaft to the later model gearbox.