This is a page explaining some of the differences between the 73-87 GM light duty truck, Blazer, Jimmy, and Suburban model line. This information may be helpful when identifying a particular model or part, and it will also aid in any "will this fit my truck" questions you might have running through your head. If you happen to know something that isn't already included on this list, feel free to contact me so it can be added. Thank you.
1973 was the first year of the new body style for the GM truck line. The new body style featured sculptured sides, squared-off wheel openings, 21% more glass area (with enclosed antenna), and a roomier cab with flow thru ventilation. The frame rail thickness was increased, the gas tank was moved out of the cab to the right-side frame rail, and a new energy absorbing steering shaft was added. Suspension wise, the wheelbase increased (2.5 inches for swb and 4.5 inches for lwb), front spring rates were reduced, a front stabilizer bar was added to improve ride and handling, front disc brakes were now standard, and the rear shock absorbers were staggered to reduce axle hop. New to the lineup was a factory crew cab (3+3) dooley, and a four door Suburban (67-72's were three door). Engine wise, 1973 was the last year for the 307 V8 and the 454 now replaced the 402.
Not too much changed in '74, but above the door rain gutters were now available. Full-time 4WD was introduced to the pickup line when the NP203 transfer case was made available in V-8 models. 1974 was also the last year for the recessed "egg crate" grill, making the '73 & '74 grills unique to these two years. GMC was also the official truck of the Indianapolis 500 in 1974...as well as in 1975, '76, '77, '80, '81, '83, '84, and '85.
In 1975, GM changed its model line around a little. Custom line is dropped and Custom Deluxe becomes base model. Cheyenne Super is replaced by Silverado as top trim level. Upper trim levels receive brushed aluminum panels on tailgate. Scottsdale line is also added to the 1975 line-up. On the interior, the windshield wiper switch location is no longer back lit like the '73 & '74 models were, not to mention the switch itself is in a slightly different location, thus making the '75 and up dash bezels slightly different. Rain gutters are now standard equipment on all models as is the new quick release tailgate for the fleetside models...and a new folding seatback option is now available. C20 model was made available in a 4 door model minus rear seats. HEI ignition becomes standard equipment, catalytic converters were also made standard equipment on all trucks under 6,001 gross vehicle weight (GVW). 400 small block is available in 4x4 models, and changes to the grille make it flush to the front and give it three horizontal bars. 1975 is also the last year for the full convertible top Blazer and Jimmy as well as the last year engine displacement badges were used on the grills.
New Zinc rich primer is added to aid rust prevention. Deluxe chrome bumpers with rubber impact strips are a new option. Rally wheels and a Sport model are now also offered as options. "Bonanza" trim package introduced and marketed as a "value" for customers, as three levels are available (YG6, YG7, YG8). 1976 was also the first year that white was not the only option for a secondary color on two-tone equipped models. Last year for Chevrolet Orange engines. The Blazer gets a slightly new body design with metal roof over front seats and fiberglass over the rear, which is still removable like previous years. Instrument cluster wise, a new "volt" gauge replaced the previous "amp" gauge.
1977 was the first year power windows and door locks were offered as well as intermittent wipers. Along with that, the inner doors, door panels, and internal door parts were different than the 73-76 models. 1977 was also a transition year for bucket seats...early production 77's had low back bucket seats while later production 77's had high back bucket seats. There was also a new grille design eliminating four of the vertical dividers and one of the horizontal, and an inside hood release was now offered. Trim wise, 1977 was the only year to have a yellow/gold stripe in the center of the side and rear moldings...however, the 1975 GMC Gentleman Jim had this trim as well. The 305 V8 was introduced along with styled (wagon) wheels without center caps. One-ton (K30) models were introduced to the line-up, and with them Bonus Cab and Crew Cab models. Finally, an optional rear defroster was also offered.
The most notable change in 1978 was the offering of a 5.7 350 (22.5:1) Diesel engine in the C10 pickups. Frame changes were made to fit new catalytic converters required on California trucks, and dual-exhaust options were not available in California. On trucks with V-8s and full-time 4WD, struts were incorporated between the engine and transmission, and between the transmission and transfer case. The top trim level Silverado now gets new brushed aluminum trim while the wood grain trim is now history. A new gas filler door was added, replacing the flush mounted gas cap. The Blazers and Jimmys now had a recessed floor for the rear passengers increasing leg room, and the rear seat now folded down for quicker and easier load carrying tasks. Electrically, sometime during the '78 model run, the glass fuse box was replaced with the now common spade type fuses. 1,317,466 trucks sold this year setting a new record. Chevrolet was also the official truck of the Indianapolis 500 in 1978...as well as in 1982 & 1986. Overall, GM trucks were the official truck of the Indy 500 twelve times during the 73-87 model run.
GM begins making changes to the front end by combining headlight bezels and turn signals, a new apron is added below the grille, a decorative ridge was added to the leading edge of the hood, and new paint schemes were available. Catalytic converters are now standard on all trucks with GVW up to 8,500 pounds.
1980 was a slightly odd year. Rectangular headlights were now included on the Silverado models, while the rest still received 1979 style round headlights. New "egg crate" grille, below eye line mirrors, 8-track and cassette options, and cast aluminum wheels. Dual exhaust was also offered on the 292 six-cylinders. The NP203 transfer case was discontinued. All K-series trucks were outfitted with part-time NP205s. The 400ci V-8 was no longer available in K10s. The K20 series was aligned more closely with the K30 series to avoid the use of catalytic converters in 8,600-pound GVWR models. Fuel prices were rising and that negatively impacted truck sales.
Complete re-styling of the front end debuted in 1981. The re-styling of the trucks boasted a weight reduction of up to 300 pounds. With the new grill design, the trucks came equipped with: quadruple headlights (however, two were still being offered), horizontal side marker lights, new bumpers, and a slightly different tailgate. Front sheet metal remained the same through 1987. The interior changed slightly with a new dashed shape, seats, instrument panel, and sill plates. There were many power train changes, and included was the introduction of the NP208 transfer case for K10 and K20 trucks; the inclusion of automatic locking hubs and quad shocks on all K-trucks; the discontinuation of the 400ci V-8; the introduction of the 454ci big-block to the K-series line; and the introduction of two 305ci V-8sa 49-state version and a California-only version. This brought the total number of engines available on K-trucks to eight. The fuel tank was moved to the driver-side frame rail. 1981 was also the last year for the 12 bolt differential, replacing it was the 10 bolt.
New features became standard equipment on the 1982 trucks. Chevrolet standardized the chrome grille on all trucks as well as the front bumper. Transfer case gears in the K30 trucks were now synchronized, allowing shifts to 4-Hi at speeds under 25 mph and power steering is now standard on all K-series trucks. Chevrolet introduces the 6.2 litre GM Diesel with automatic overdrive transmission (700R4), and the 305 (5.0) 2 barrel was now discontinued. On all 20 and 30 series trucks, 16 inch wheels are now used instead of the 16.5 inchers. Cheyenne model is dropped from the lineup. Sadly, 1982 was also the last year the 2 wheel drive Blazer could be had from GM as well as the soft top option. Chevrolet became number one in truck sales in 1982.
Chevrolet continued making cosmetic changes to the C/K line. Turn signals were moved from the bumper to behind the grille. Chevrolet also offered the automatic 700R4 transmission as an option.
For 1984, the quadruple headlights were now made optional. Interior received changes to the wiper controls and the integration of the high beam lights and cruise control being moved to turn signal stalk. The 4.3L (262ci) V-6 replaced the 250ci inline six as the standard K10 engine. Chevrolet sold 30,000 K-series trucks and 23,000 Blazers to the U.S. Army.
GM's most notable change this year was the introduction the Vortec V6 with a 4-barrel carburetor. The grill was once again changed and Chevrolet added the "Custom Two-Tone" paint option.
There were no major changes to the trucks functionality or design.
GM changes name designation on the C/K line of pickups. The previous 4x2 C series is changed to the R series, and the 4x4 K series is changed to the V series. Chevrolet also introduces TBI equipped engines and computer ignition controls (although carburetors were still available in some models). 1987 was also the last year for the "stepside" bed, starting in 1988 GM refers to it as a "sportside". The end of a 15 year run for the rounded line C/K pickups, however, the rounded line body style remained until 1991 on Blazers, Suburbans, and one-ton trucks.
There were no major changes to the Blazers, Suburbans, or crew cab's functionality or design.
In 1989, the Blazers, Suburbans, and crew cabs got a makeover, with the changes consisting of a new grill treatment to try and make them look like GM new body style of trucks. They also received the new 4 spoke steering wheel and the Suburban received an optional overhead console. Also new for the '89 models were 30 spline front and rear axles.
The only new changes for 1990 was the addition of a power mirror option for the Blazers and Suburbans as well as the replacement of the 208 transfer case with the 241.
In 1991, the 3/4 ton crew cabs, Suburbans, and one ton trucks received the 4l80 transmission.