What Is an OBS Chevy Truck?

Most Bowtie enthusiasts will tell you that Chevy/GMC OBS trucks are the GMT400 C/K platforms, which were produced from 1988-1998, with the exception of the C3500HD Chassis Cab, which continued production until 2002 in the old body style. 

The OBS Chevy GMT400 featured significant engineering updates that improved its comfort and reliability, like an independent front suspension and wider frame to accommodate an inboard fuel tank design. These new features, combined with more modern conveniences and renowned Chevy-truck durability, ushered in a generation of trucks that are in high demand in the classic truck market.

The most recognized engine across OBS Chevy trucks was a 5.7L small-block V8, including the Vortec 5700 in later GMT400 years, and the most desirable gas engine was the 7.4L 454 high-output that came in the limited-production Chevy 454 SS sport truck from 1990-1993. Other engines in these Chevy/GMC OBS trucks included a 4.3L V6, 5.0L V8, 6.2L Diesel and 6.5L turbo Diesel. 

OBS Chevy trucks built on the GMT400 platform were available in C/K configurations. For instance, any C2500 Chevy/GMC truck of the OBS era is a two-wheel-drive ¾-ton Chevy or GMC truck, and a K1500 is a four-wheel-drive half-ton OBS Chevy/GMC truck. These trucks were offered with 1500 (half-ton), 2500 (three-quarter ton), and 3500 (one-ton) chassis, in regular and extended-cab layouts, with crew-cab configurations joining the GMT400 lineup for 1992 on 3500 models. Earlier 1988–1991 crew-cab 3500 trucks existed, but those were R/V-series carryover models from the previous Squarebody platform, not GMT400 OBS trucks. 

The early OBS Chevy trucks featured a simple, blocky interior design that emphasized functionality (and cost savings) over style. The dashboard had a blunt, boxy, appearance, with bar-graph analog gauges in plastic utilitarian enclosures, the door panels were plastic, and the seats, generally bench style, were wrapped in cloth or vinyl. In 1995, OBS Chevy trucks received a major refresh starting with a new dashboard that was softened and featured an ergonomic design, higher-quality door panels, center mounted radio (replacing the high-mounted cassette player), an HVAC system with dials instead of levers, updated seat designs and a driver’s side airbag.

Are all C/K Chevy and GMC Trucks OBS?

No. C/K does not mean a Chevy truck is OBS, as OBS is associated with GMT400 Chevy C/K and GMC Sierra trucks. While all Chevy/GMC OBS trucks have C or K nomenclature, the C/K designation began long before the GMT400 OBS Chevy truck generation began. These letter designations started with the 1960 model year to differentiate between a two-wheel-drive Chevy truck (C), and four-wheel-drive Chevy truck (K). The C/K designation carried on through the OBS Chevy truck era and ended in 1999, although it was used as an internal designation in GM until 2002. 

Squarebody Chevy/GMC trucks were produced from 1973-1987. These were C/K pickups, with the R/V carryover models continuing through 1991 during the GMT400 transition. If you covered them and lined them up, they would look similar, but Square Body Chevy/GMC trucks are not built on the GMT400 platform, and are technically not considered OBS Chevy trucks. 

OBS Chevy/GMC trucks do have Fleetside and Sportside variants, but bed style is not what classifies them as Old Body Style Chevy trucks. Fleetside refers to the smooth-sided pickup bed with the wheel wells inside the cargo box, while Sportside refers to the GMT400-era stepside-style bed with external rear fenders and a narrower cargo floor. Fleetside was already part of Chevy truck vocabulary when the C/K line launched in 1960, while Chevrolet used Stepside and GMC used Fenderside for earlier external fender beds. During the GMT400 era beginning in 1988, GM used the Sportside name for its updated stepside-style bed design. Chevrolet’s Sport Equipment Package shifted from a Fleetside bed to a Sportside bed for 1993, while GMC references to Sportside appear as early as 1990. The Sportside name continued into the GMT800 era before the bed style was discontinued for 2006. 

From bed protection and security to storage solutions, stopping power, interior upgrades, and performance products that will make your OBS Chevy truck “go”, there is no shortage of parts available to enhance your legendary Chevy or GMC truck. Check out the most popular items in the categories below.

Secure cargo and protect your OBS Chevy’s bed from elements with a best-selling hard-folding tonneau cover.

Adding seat covers to Chevy/GMC C/K pickups is the perfect way to protect the integrity of original interiors and enhance the look of seats that show severe signs of wear.

Improve stopping power, and increase engine performance with the best products for your OBS Chevy truck.

Q: What Years of Chevy Trucks Are OBS?

Chevy/GMC OBS trucks were produced from 1988-1998 on the GMT400 C/K platforms, and include the 1991-2002 Chevy/GMC C3500HD Chassis Cab, which continued production until 2002 in the old body style.

Q: What Are the Most Popular OBS Chevy Trucks?

The most popular OBS Chevy/GMC trucks are the 1996-1998 C1500/K1500 with the 5.7L V8 (Vortec 5700), thanks to its broad enthusiast appeal and updated features compared with earlier GMT400 trucks. The most desirable Chevy OBS truck is the 454 SS C1500, which came stuffed with a 7.4L 454 big block under the hood. 

Q: What Is the Difference Between the GMT400 and GMT800?

GM’s GMT400 platform underpinned the OBS generation of Chevy/GMC trucks that were built from 1988-1998. The GMT800 followed the GMT400 and was in production from 1999-2007. The GMT800 is referred to as the new body style, or NBS Chevy/GMC truck.