Everything Chevy Fans Should Know About 'OBS' Trucks

Humans love to attach labels and acronyms to just about everything. From sports (MLB, NFL, NBA) to government entities (FBI, IRS, NATO), people (JFK, LBJ, RBG), and everything in between (IBM, NBC, YMCA), we can't stop shortening the name of things. Even our texting "language" is filled with acronyms ("LOL," "OMG," "TGIF").

Car enthusiasts are no different. Between what is generally considered the decade from 1988 to 1998, Chevrolet trucks were built on the C/K GMT400 body style (some sources include trucks through 1999, while others say 2000 or even 2002). Now, they're known colloquially as "OBS" trucks: the term can mean "old body style" or "original body style," but both mean roughly the same thing.

The confusion stems from the fact that both Chevy and GMC shared the 4th generation C/K platform (internally referred to as "GMT400"), but named their respective trucks differently. Chevy used C/K, while GMC's full-sized truck was known as the Sierra. 

After a few years, the C/K platform naming convention was used by both on the big SUVs as well. It can be found on the Chevy C/K, Blazer, Tahoe, and Suburban, while GMC used it on the Sierra, Yukon, and its own iteration of the Suburban. So ... not confusing at all.

Chevy/GMC "Square Body" trucks that came before the GMT400 typically apply to models made between 1973 and 1987. Trucks that came after (between 1999 and 2006) are referred to as GMT800s. The GMT400s are generally considered the sweet spot between the uber boxy "Square Body" trucks, and the softer rounded edges of the 800s.

Several technical innovations also elevated the 400s above the old-school bucket of bolts from earlier trucks. These OBS trucks were assembled via the latest computer-aided design (CAD) programs, used more galvanized steel, and had a fully welded frame.

A number of firsts appeared during this era of truck, including anti-lock brakes (ABS), an extended-cab, and in 1995 had a driver-side airbag (dual airbags came in 1998). It was also the first time General Motors (GM) used shift on the fly four-wheel drive (instead of locking hubs), and an independent torsion-bar and CV joint suspension on its K-series trucks. The standard engine was a 4.3-liter Vortec V6 with plenty of torque, and later, both 5.0-liter V8s and 8.1-liter engines became available.

That's not to say they weren't without issues. Motor Trend points out they tended to become heavily rusted, dashboards often cracked due to the cheap plastic used, the paint faded, the clear coat oxidized, and the brakes were too small. Despite their failings, these old-body-styled GMT400 trucks hold a unique place in the evolution of the pickup that has made them the perfect vehicle for enthusiasts to retrofit and customize — so much so that their value has taken off in recent years.

Hagerty states that Chevy GMT400s trucks have increased in value by 63% over the last three years, while GMC's 400s are up 52%. An equally-telling statistic is that quotes for insurance on these trucks are up 58% and 53%, respectively.