Squarebody vs. OBS: Key Differences Between the 1973-87 and 1988-98 Chevy & GMC Trucks

Shopping for a classic Chevy or GMC and stuck on the squarebody vs OBS question? These two truck generations look like cousins, but under the skin they are very different machines with parts that do not swap back and forth. This guide breaks down exactly what separates the 1973-87 squarebody from the 1988-98 OBS so you can buy, restore, or part-shop with confidence.

Quick answer: The squarebody (1973-87) and OBS (1988-98) Chevy and GMC trucks share a family resemblance but are fundamentally different vehicles. The squarebody uses an older boxy body-on-frame design with a solid front axle on 3/4-ton and 1-ton models and fully separate, flat body panels. The OBS introduced the GMT400 platform, aerodynamic styling, and independent front suspension across every model. Sheet metal, glass, interior, and most suspension parts do not interchange between the two generations.

What Is the Squarebody?

The term “squarebody” refers to the third-generation Chevy and GMC full-size pickups produced from 1973 through 1987. They earned the nickname from their boxy, upright styling: flat panels, 90-degree corners, and a bold chrome grille. The squarebody replaced the rounded “Action Line” trucks of 1967-72 and went on to become one of the best-selling vehicle families in American history. For a deeper year-by-year breakdown, see our full model years guide.

The squarebody designation covers a broad lineup:

• C/K 10, the 1/2-ton pickup (by far the most common)
• C/K 20, the 3/4-ton pickup
• C/K 30, the 1-ton pickup
• Suburban, the extended body on the C/K chassis (ran through 1991)
• Blazer and Jimmy, the 2-door SUVs on the C/K chassis (ran through 1991)

Remember the letter code: C means 2WD and K means 4WD, while 10, 20, and 30 mean half-ton, three-quarter-ton, and one-ton. If you want to dig into the drive-type differences, our C10 vs K10 comparison covers fitment and parts in detail.

What Is the OBS?

OBS stands for “Old Body Style,” a retronym applied after the 1999 redesign pushed these trucks into “old” status. The OBS trucks (1988-98) are the fourth-generation Chevy and GMC full-size pickups, built on the GMT400 platform. They brought aerodynamic curves, a steeply raked windshield, plastic cladding, and a heavily modernized interior. Despite wearing the same Chevy and GMC badges, the OBS and squarebody share almost no sheet metal or major mechanical parts.

Squarebody vs OBS: Side-by-Side Comparison

Feature	Squarebody (1973-87)	OBS (1988-98)
Styling	Boxy, upright, 90-degree body lines	Rounded, aerodynamic, raked windshield
Platform	GMT-era body-on-frame	GMT400 body-on-frame
Front suspension (1/2-ton)	Independent front suspension (IFS)	Independent front suspension (IFS)
Front suspension (3/4 & 1-ton)	Solid front axle (Dana 44/60)	Independent front suspension (IFS)
Cab design	Upright, squared windshield	Raked windshield, aerodynamic roofline
Interior	Simple, analog, minimal electronics	Modern, optional console, improved dash
Engine options	Small block V8, big block V8, inline-6	Small block V8, V6, Vortec (later years)
Fuel system	Carburetor (most), early TBI (1987)	TBI, then CSFI (1996+)
Parts availability	Excellent reproduction support	Good OE supply, less reproduction focus

Body Panel Differences: Do They Interchange?

No. The body panels between the squarebody and OBS are completely different. The squarebody uses its own cab architecture with a more upright windshield angle, a shorter hood, and different door opening dimensions. The OBS redesigned every panel for the aerodynamic body style.

This matters enormously for restoration. Cab corners, floor pans, fenders, doors, and glass are all generation-specific. A squarebody cab corner will not fit an OBS, and the reverse is equally true. When you source panels, confirm the year range matches your generation first. Reproduction squarebody body panels such as fenders, bedsides, and wheelhouses are widely available, which is a big part of why these trucks are so restorable.

Interior and Trim

Dashboards, door panels, gauges, and seats are all unique to each generation. Squarebody interior parts, from dash bezels to door pull straps, are reproduced specifically for the 1973-87 cab. OBS interior parts will not bolt in. Likewise, exterior trim like grilles, bumpers, and emblems are styled for their own era and do not swap.

Suspension Differences

The single biggest mechanical difference is the front suspension on the heavy-duty trucks:

• Squarebody 3/4-ton and 1-ton: Solid front axle (Dana 44 on the 3/4-ton, Dana 60 on the 1-ton). Heavier, more rebuildable, and preferred for serious off-road use.
• OBS 3/4-ton and 1-ton: Independent front suspension on all models. Smoother on the road, but more complex to service and less durable under hard off-road stress.

Both generations use independent front suspension on the half-ton, with upper and lower control arms and coil springs. The basic architecture is similar, but the geometry and individual parts differ, so components do not cross over.

Engine and Fuel System Differences

Most squarebody trucks use a carburetor for fuel delivery, while the OBS moved to fuel injection. The 1987 model year introduced Throttle Body Injection (TBI) on some squarebody engines, so a 1987 truck can be either carbureted or TBI depending on the engine and application.

For restoration, this means fuel system parts are mostly generation-specific. The mechanical fuel pump on a carbureted squarebody is not the same as the electric pump feeding an OBS TBI system. A squarebody that runs a carburetor is simpler to diagnose and service, which is a real advantage for a first-time project.

Both generations offered the familiar Chevy 305 and 350 small blocks and the 454 big block, but the supporting systems differ. The squarebody relies on a distributor with points or early HEI ignition and a simple vacuum-advance setup, while later OBS trucks add engine computers, sensors, and injection hardware. If you want a truck you can tune with hand tools and a timing light, the squarebody is the easier platform to live with.

Driving Feel and Frame

On the road, the difference is immediately obvious. The squarebody rides and steers like the truck it is, with a recirculating-ball steering box, a taller greenhouse, and a more vertical seating position. The OBS feels more car-like thanks to its aerodynamic body, softer suspension tuning, and quieter cab. Neither frame interchanges, and cab mounts, bed mounts, and crossmember locations are all specific to each generation, so a squarebody cab will not drop onto an OBS chassis without heavy fabrication.

Which Generation Is Better for Restorations?

Both are popular, but the squarebody has a clear edge in the restoration market:

• Simpler mechanicals: A carbureted squarebody is easier to work on and diagnose than a fuel-injected OBS.
• Classic styling: The boxy look is enjoying a major resurgence, especially for the patina and shop-truck aesthetic.
• Parts availability: Nearly every rust-prone squarebody panel is reproduced as a new part.
• Affordability: Squarebodies are generally cheaper to buy and restore than comparable OBS trucks.

If you are weighing a purchase, our squarebody buying guide walks through what to look for and which years hit the sweet spot. You can also browse the full FAQ page for any question about fitment and ordering.

Final Recommendation

To identify which generation a truck is, start with the styling: upright and boxy is squarebody (1973-87), rounded and aerodynamic is OBS (1988-98). The VIN confirms the exact year. Because parts do not cross between generations, verifying the year before you order is always the right move. If you own a squarebody, our entire catalog is built around the 1973-87 platform, so every panel, seal, and trim piece is matched to your truck.

A few squarebody-specific parts to get you started: a reproduction front fender for the 1973-80 trucks, a factory-style door weatherstripping kit, a correct grille kit for the early front end, and an OE-style rocker panel. None of these fit an OBS, which is exactly the point.

Frequently Asked Questions

What year did the squarebody end?

The squarebody pickup ended after the 1987 model year. The Suburban and full-size Blazer and Jimmy continued on the squarebody platform through 1991 before the GMT400-based replacements arrived.

Is a 1988 Chevy truck a squarebody?

No. The 1988 Chevy and GMC trucks are OBS (GMT400 platform), not squarebody. The squarebody pickup ended with the 1987 model year. The difference is obvious at a glance: 1988 and newer trucks have a sloped windshield and rounded body lines.

Do squarebody and OBS trucks share any parts?

Very few. Some brake components and engine accessories may carry over, but body panels, interior parts, suspension geometry, and frame components are generation-specific. Always verify fitment for your exact year before buying.

Why are squarebody trucks so popular right now?

The squarebody renaissance is driven by several factors: the trucks are now 35 to 50 years old and hitting classic status, the boxy styling matches current design trends, the mechanical simplicity makes them approachable for DIY owners, and the deep reproduction parts market makes a full restoration realistic.