The Chevy K5 Blazer was introduced with the ’69 model year and was based largely on the C/K pickup chassis of the day. It spanned a domestic manufacturing life of about 25 years. The last year of production for the United States was marked by the ’94 model, although export models continued for about seven more years.
The Blazer was a staple fullsize SUV, initially built with capable straight axles, V-8 engine options, and room to take an entire family into the backcountry camping or exploring. Many were kept in stock form, but the chassis and drivetrain leant themselves readily to modifications for more serious dirt use. The fullsize Blazer remains an off-road classic today.
1st Generation (1969 to 1972)
The earliest Blazers built from 1969 to 1972 (the similar GMC Jimmy debuted in 1970) offered GM buyers a short-wheelbase fullsize SUV on a ladder frame similar to the trucks of the day. The Blazer sat on a 104-inch wheelbase and offered a removable fiberglass hardtop. For the first year, only 4WD models were available, but afterward, both 2WD (coil-sprung IFS) and 4WD models were offered. We’re concerned here primarily with the 4WD models. At the time of its introduction, the Blazer was advertised as having short-wheelbase prowess with wide-track stability, presumably in contrast to its Ford Bronco and International Harvester Scout competitors of the time.
The Blazer was introduced with a leaf-spring suspension and straight axles, as was common in the day. Power steering was via a recirculating ball Saginaw steering box mounted to the driver-side framrail with a push-pull-style drag link connecting the pitman arm to the steering knuckle on the front axle.
A number of carbureted engines were offered in the early models. These included the 250ci I-6, 292ci I-6, 307ci V-8, and 350ci V-8. The automatic transmission choice was the TH350. Manual transmission choices were the column-shifted three-speed (usually found behind the I-6 engines) or the floor-shifted Saginaw SM465 four-speed with a 6.55:1 First gear. The iron-case, gear-drive T-case was either a Dana 20 (2.03:1 low range) or a NP205 (1.96:1 low range). A PTO output at the T-case was also available during the early years of the Blazer.
GM varied the axle gearing over the years to accommodate the various engines, transmissions, and tire sizes. Axle gearing in first-generation Blazers was often either 3.73:1 or 3.07:1. The front axles were Dana 44 units with manual locking hubs, while the rear axles were GM 12-bolts.
2nd Generation (1973-1991)
GM did a major body redesign for the ’73 model year, drastically changing the exterior appearance. The wheelbase was stretched 21⁄2 inches, and the overall length grew a bit as well. In 1975, we chose the Chevy Blazer as Four Wheeler of the Year.
In 1973, there was a new hardtop style with a roll-up tailgate window. Up until 1975, the removable hardtop lifted away all the roof behind the windshield whenever it was removed. Starting in 1976, a new steel half-top design with a built-in rollbar was put into production. With the new design, only the roof near the B-pillar rearward was removable. In 1981, there was a new aerodynamic front-end styling introduced, and in 1989 GM again changed the front grille.
Engine choice through the second-generation years included the 250ci I-6, 307ci V-8, 305ci V-8, 350ci (5.7L) V-8, 400ci V-8, and 6.2L diesel. Behind these sat a three-speed column-shifted manual or TH350 auto transmission up through 1981. All years offered the SM465 manual, and the TH700-R4 four-speed automatic was used starting in 1982.
In 1975, the Blazer came equipped with a new transistorized high energy ignition (HEI) system boasting 35,000 volts at the spark plugs. The mechanical moving ignition parts were replaced with a magnetic pulse generator and electronic control module. In 1981, the Blazer began to come equipped with Electronic Spark Control (ESC) to automatically retard timing when engine knock was detected. Also in 1987, throttle-body fuel injection was introduced. The year 1989 saw the introduction of a serpentine belt on the 5.7L V-8.
Transfer cases used varied through the years, including the holdover Dana 20 (1973-1974) and NP205 (1973-1980).
In 1973, GM also introduced full-time 4WD in the Blazer. An interaxle differential in the iron-case, chain-drive NP203 transfer case (2.01:1 low range) provided driving force to both the front and rear axles, while compensating for speed variations between them. This eliminated the need for locking front hubs. When off-road or on loose surfaces, the interaxle differential could be disabled, locking the drive to the front and rear axles together. Locked and unlocked transfer case modes were available in both high and low range. Shifting the transfer case selected the different modes.
By 1976, full-time 4WD was standard on all Blazers with automatic transmissions. Conventional 4WD with locking hubs remained available with the manual transmissions.
In 1981, GM went to a lightweight aluminum NP208 transfer case (2.61:1 low range) with synchronizers and automatic locking front hubs. This setup allowed drivers to shift from 2WD to 4WD at speeds under 25 mph. In 1989, the transfer case was again changed to the NP241 planetary design with 2.72:1 low range gearing.
The front axle was initially a Dana 44 in the early second-generation models but changed later to the GM 10-bolt axle. There were some crossover years when both axles were available from about 1977 to 1980. Early rear axles were the Corporate 12-bolt, and later axles were the 10-bolt variety, with crossover years of 1979 to 1981. Axle gearing over the years ranged from 2.56:1 to 4.11:1. Contrary to limited convention, there was no 12-bolt front axle.
Interior amenities were improved in 1978 with the addition of power windows, power door locks, high-back bucket seats, and fold-up rear seat. A top-of-the-line Silverado trim was introduced on the Blazer in 1980.
3rd Generation (1992-1994)
For the ’92 model year, the Blazer converted over to the GMT400 series platform, one the fullsize Chevy trucks had been using since 1988. Wheelbase was stretched to 1111⁄2 inches, the longest yet, but still shy of its bigger Suburban sibling. The new body design eliminated the removable hardtop and double rear doors were offered as an option on some models.
The L05 5.7L TBI V-8 was used along with a Getrag 290 five-speed manual overdrive transmission, or 4L60 four-speed automatic transmission, which was upgraded to the electronic 4L60-E version in 1993. There were also some late third-generation Blazers that came with the 6.5L turbodiesel V-8.
This model was offered standard with the Insta-Trac 4x4 system with the NP241 transfer case (2.72:1 low range) that let you shift from 2WD to 4WD high range and back, while moving. It was also equipped standard with a four-wheel anti-lock brake system.
Probably the most startling change to the Blazer was the move from a solid front axle to fully independent torsion-bar front suspension. The front differential used was the GM 8.25-inch IFS centersection, while the GM 10-bolt continued to serve in the rear. Axle gearing ranged from 3.42:1 to 4.10:1.