Tranny Choices
With only three manual transmissions and three automatics to chose from, it's pretty hard to make a poor choice. The three-speed stick was shifted on the column and is the least common (and least desirable) choice. A manual four-speed with overdrive was made for a few years, but it's also not very common. The manual four-speed SM465 is a floor- shifted, granny low box that has a virtually untarnished reputation and is a favorite of gear-grinders. The TH350 and TH400 are almost indestructible if not overheated and are arguably two of the best autos ever produced. The 700-R4 four-speed auto features an overdrive gear for highway cruising and mileage, but during the first few years of production, it was plagued by problems that have since been sorted out.
T-Case Tips
Only three different transfer cases were used from 1973 to 1987: the NP205, NP203, and NP208. Only the NP205 is available in all these years, and it's regarded as the toughest style around for regular pickups, as evidenced by the usage in the 1-ton models. The 205 is a simple, relatively light geardriven unit with part-time operation. It's identifiable by the three-bolt retainer (seen on the back of the case) that holds the shaft that goes through the center of the cast-iron case. From '80-'91 the ¾-ton and 1-ton versions used a long slip-yoke-style extension housing similar to that seen on NP208s.
The full-time NP203 used from 1973 to 1979 was a heavy (heavy) but durable chaindrive style identified by the two-piece tailhousing made of iron or aluminum. Both the NP203 and the NP205 suffered from a 2.0:1 low-range ratio, which was deemed adequate for the era when low axle ratios were available. The chaindrive, part-time NP208 was introduced in order to save weight. The NP208 low range is a respectable 2.61:1.
Differentials
Front and rear axle styles didn't vary greatly except for weight ratings between models, and most of them are easily interchangeable. The cover bolt count and design are the easiest ways to identify the model, as is the amount of wheel studs used per wheel. Front axles for K10s and most K20s were either the Dana 44 with 10 bolts on the cover and an angular shape, or the Corporate 10-bolt with an ovalish cover and 10 bolts. The 10-bolt and Dana 44 used ball joints in the steering knuckles with a three-bolt steering arm. The K10 series used six-lug wheels, and the K20s were fitted with eight lugs. The K30 models received Dana 60 front axles with a 10-bolt angular-shaped cover that's much larger than the 44. The wheels were eight-lug but with 9/16-inch studs instead of the K20's ½-inch style. Chevy Dana 60 steering arms were fitted to the knuckle with four bolts instead of three.
Rear axles used on the K10 were Corporate 10- or 12-bolt designs, with the identifying features being the number of bolts in the cover. The K20 and K30 used a 14-bolt cover, except for the dualie Crew Cab, but two different shapes of covers and ring gear diameters were used. The 9 ½-inch 14-bolt had a smooth-sided cover, while the larger 10 ½-inch style was sharply angular and had a bolt-on pinion bearing support unlike the smaller style. Except for the 10-bolt unit, these axles are more than adequate for most types of 'wheeling. And the Crew Cab "Doolie" used the dual-rear-wheel Dana 70. Dualie front Dana 60s were also slightly different from single-rear-wheel versions.