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Chevy Suburban Spotter's Guide - SUV Bio

Posted in Features on April 27, 2015
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Some say the modern Chevrolet Suburban’s roots began with the introduction of the Suburban Carryall in 1935. Then in 1957, the first 4WD Suburban was introduced. When it came time to pack a lot of people and cargo into a 4WD, the Suburban was a viable choice. We’ll look at the most common and desirable ’67-’99 Suburbans.

7th Generation (1967-1972)
The Chevy 1⁄2-ton pickup line received all-new styling for the ’67 model year, and the Suburban was redesigned at the same time. It had a single door on the driver side, with front and rear doors on the passenger side. A 3⁄4-ton version Suburban was also available and GM began using the C/K designations, where “C” indicated two-wheel drive and “K” indicated four-wheel drive. We’re concerned here primarily with the 4WD models.

The ’67 models were a whole new version of the Suburban, an evolving Chevrolet wagon that had been in production in various forms for over three decades. By this time, Suburban was available in 1⁄2-ton and 3⁄4-ton models in 2WD and 4WD.

This fullsize SUV sat on a ladder frame similar to the trucks of the day and had a wheelbase stretching 127 inches and an overall body length just over 215 inches. It sat on a leaf-spring suspension and utilized straight axles for simplicity and ruggedness. Power steering was typically optional. These Suburbans started out with four-wheel drum brake systems but offered front discs beginning with ’71 models and power-assisted disc/drum systems a year later.

A number of carbureted engines were offered in the early models. These included the 250ci I-6, 307ci V-8, 350ci V-8, and 400ci V-8. Manual transmissions were common with a column-shifted three-speed being the most basic unit. A floor-shifted SM420 four-speed with 7.06:1 First gear was offered in the inaugural year, followed by the floor-shifted Saginaw SM465 four-speed with 6.55:1 First gear for many years to come. Early ’70s automatic transmissions would simply be three-speed units, either the TH350 or TH400.

The Suburban was built as a wagon that could carry far more cargo weight than the typical station wagon, or one could add rear seats and carry up to nine people, plus some cargo. The seventh-generation Suburban would grow the wheelbase from 127 to 1291⁄2 inches.

For the first two production years, the iron-case, gear-drive transfer case was a Rockwell T-221 with 1.86:1 low-range gearing. Starting in ’69, the iron-case, gear-drive transfer case was either a Dana 20 (2.03:1 low range) or a NP205 (1.96:1 low range). A PTO output at the transfer case was also available during the early years of the 4WD Suburban.

GM varied the axle gearing over the years to accommodate the various engines, transmissions, and tire sizes. Gearing in seventh-generation Suburbans was often either 3.73:1 or 3.07:1, but some later models had lower 4.10:1 or 4.56:11 gearing. The front axles were Dana 44 units with manual locking hubs. The 1⁄2-ton model used a standard Dana 44, while the 3⁄4-ton model had a heavy-duty version. Both were closed-knuckle design through ’70. Rear axles were typically a GM 12-bolt or Dana 60 on seventh-generation 1⁄2-ton models, and GM HO72 (commonly referred to simply as an Eaton rear) or Dana 60 on the 3⁄4-ton models. The heavier Suburbans often had full-floating rear axles. Limited-slip differentials were an option in the rear axle.

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8th Generation (1973-1991)
The Suburban got a major body redesign for the ’73 model year when the new Chevy trucks were introduced. This was the first year it was offered in a four-door body style. The wheelbase was stretched 21⁄2 inches, and the overall length grew several inches longer as well. The body was again available with double rear doors or a tailgate with a retractable window. The frame was completely redesigned and strengthened for the new generation, and towing capacity was improved.

For the straight-axle, leaf-spring suspension models, lift kits are plentiful and reasonably priced. The ’92-newer Suburbans have IFS which makes for a smoother highway ride but is overall less off-road capable, and lift kits are more complex and costly compared to the straight-axle versions.

Engine choice through the eighth-generation years included the 250ci I-6, 305ci V-8, 350ci V-8, and 400ci V-8. This was also the first year of the K20 3⁄4-ton model that could be optioned with a 454ci V-8. The 6.2L V-8 diesel was introduced in the ’82 trucks. Transmissions included the three-speed column-shifted manual (until about ’79 vehicles) or TH350/TH400 auto transmissions up through about ’81 models. The SM465 manual was offered until about the ’90 model, and the TH700-R4 four-speed automatic was used starting in the ’82 vehicles.

GM’s transistorized 35,000V high-energy ignition (HEI) system was introduced in ‘75 trucks to replace the mechanical moving ignition parts with a magnetic pulse generator and electronic control module. In the ’81s, GM offered Electronic Spark Control (ESC) on some engines to automatically retard timing when engine knock was detected. Also, throttle-body fuel injection (TBI) was introduced in ’87 trucks.

One weak spot on the GM frames used with the straight-axle Suburbans is that of the steering box mount at the frame. Extended use, when combined with large tires, can weaken and eventually crack the framerail where the box is mounted. Offroad Design offers repair kits and this steering box brace to address this weakness.

The eighth-generation transfer cases included the Dana 20 (’73-’74) and NP205 (’73- ’80). Beginning with ’74 trucks, some Suburbans had full-time 4WD using the NP203 transfer case (2.01:1 low range). An interaxle differential in this iron-case, chain-drive transfer case 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.

In ’81 Suburbans, 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 ’89 models, the transfer case was again changed to the NP241 planetary design with 2.72:1 low range gearing.

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The front axle was initially a Dana 44 in the early eighth-generation models but changed later to the GM 10-bolt axle. There were some crossover years when both axles were available in the ’77-’80 trucks. Early rear axles were the Corporate 12-bolt and later axles were the 10-bolt variety, with crossover in the ’79-’81 vehicles, depending on what made its way to the assembly line. Axle gearing over the years ranged widely from 2.73:1 to 4.56:1. Rear axle traction-adding devices were typically available and a new Eaton locking differential was introduced in the ’73s.

Note that GM temporarily changed to “R” and “V” designations to denote the 2WD and 4WD models, respectively, for the ’87-’91 models. This was used to avoid confusion with Chevrolet’s newest generation C/K pickup line at the time.

9th Generation (1992-1999)
The ’92 Suburban again got a major redesign and was converted over to the GMT400 series platform the fullsize Chevy trucks had been using since the ’88 model.

The Suburban was again restyled for the ’92 model year. Wheelbase was stretched again to 131 1⁄2 inches. The new model had redesigned body lines, flush glass, and composite headlights.

The L05 5.7L TBI V-8 was the common base engine, with a 7.4L V-8 available as an option in the 3⁄4-ton model. Vortec sequential fuel injection would be offered starting in ’96 vehicles. The 6.5L turbodiesel V-8 was also introduced in ’94s to replace the 6.2L oil-burner that was discontinued a few years earlier. Four-speed auto transmissions included the 4L60, which was upgraded to the electronic 4L60-E version in ’93s and the heftier 4L80-E. Manual transmissions were dropped from the Suburban lineup.

This generation Suburban 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. Late in this generation of Suburban, GM switched from 4WD that shifted with a floor lever to push-button 4WD. This generation was also equipped standard with a four-wheel antilock disc/drum brake system.

The ninth-generation Suburban would stay in production for eight years, ending with the ’99 model. Three newer generations have followed and the model thrives to this day as General Motors’ large SUV, persisting in life as a roomy wagon with significant cargo capacity. fw

When it came to suspension, the ’92 Suburban deviated drastically from its past with a change to a fully independent torsion-bar front suspension. Rear axles on the 1⁄2-ton model were often the GM 10-bolt or GM 9.5-inch axle. The 3⁄4-ton models got the GM 9.5-inch or the Corporate 14-bolt hardware. Axle gearing ranged from 3.42:1 to 4.10:1, with the 3⁄4-ton typically getting the lower (high numerical) gearing.

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