1978 GMC K5 Jimmy - Potent

    Big-Block Power Backed Up By a Bullet Proof Drivetrain

    Ken BrubakerPhotographer, Writer

    This awesome ’78 GMC K5 Jimmy belongs to paramedic/public safety dispatcher Steve Davis of Olancha, California. Davis has done the majority of the work on this truck in the time he has owned it, and it has evolved through the years to become the incredible machine you see here.

    “I started building this truck back in 2001. My goal was to build a very capable trail rig that could also be driven on the street or highway anywhere I wanted to take it. I completed the first build in 2006. It was all leaf suspension with a Dana 44 front axle, 38-inch Swampers, and full soft top. I ran it like that for about three years, eventually scattering the Dana 44,” he says. It was because of the breakage and a terrible ride he changed to a Dana 60 front axle, 56-inch rear springs, and softer front leaves.

    My goal was to build a very capable trail rig that could also be driven on the street or highway anywhere I wanted to take it.

    This combination stayed under the rig for the next five years, but in 2011 Davis made the decision to rebuild the Jimmy. “The truck rode terrible, had a lot of rust and a host of other problems you would expect from a 25-year-old truck,” he says. So began a 2½-year rebuild of the Jimmy. “The truck was completely torn down to the frame and every part of the truck was cleaned and rebuilt or replaced. The tub’s floorboards, both bedsides, and doors were replaced. Two close friends in Ridgecrest, California, Brian Hays and Glen Westerbert (both fabricators), CAD-designed the front four-link and built all of the brackets,” Davis says. When finished, the Jimmy was what Davis had in mind. He says, “What I ended up with was exactly what I wanted in the first place. It just took a little over 10 years to get there.”

    We ran into Davis in the California desert on the Jimmy’s maiden off-road voyage. He reports that he wheeled the heck out of the rig in the Johnson Valley area and it performed well and nothing broke.

    Is the Jimmy done evolving? Nope. Davis reports that eventually it’ll get a four-link/coilover rear suspension and a new lighter-weight V-8 engine. But for now, he’s enjoying his potent Jimmy.

    When it came to restoring the Jimmys body, Davis says he did the work along with “anyone else I could get to help.” The first thing you may notice is the half-cab conversion. He says that these fiberglass half-cabs were made by a company called Creative Products that is now out of business. Nonetheless, after a bit of searching he found a used cab, made a few modifications (like adding a sliding rear window out of a mid-’70s Dodge truck), and installed the cab on his Jimmy. Since his cab didn’t come with the required bulkhead, he made one out of 1⁄8-inch-thick aluminum. The rig also received new floorboards, bedsides and doors before the exterior was sprayed Summit Racing Performance Yellow. Taking a cue from law enforcement vehicles that are often idled for long periods of time, Davis added RunCool hood louvers to help keep engine compartment temperatures under control. Moving further down on the Jimmy, Davis cut out portions of the rocker panels and replaced them with discrete but strong rocker protection made from 2x4-inch, 0.250-inch thick rectangular steel. A 1-inch Offroad Design bdy lift creates a bit more room in the fenderwells for the 37x12.50R16.5LT BFGoodrich Baja T/A radial tires. These tires are mounted on 16.5x9.75 Pro Comp Series 51 wheels outfitted with welded-on custom rock rings and inner Air Lock Internal Beadlocks.

    At A Glance
    Vehicle: 1978 GMC K5 Jimmy
    Owner: Steve Davis
    Stomping grounds: Olancha, California
    Build time: 2½ years

    Engine: GM Gen VI 454ci V-8
    Transmission: 700-R4, modified, B&M aluminum pan, Derale cooler
    Transfer case(s): Advance Adapters Atlas II
    Low range ratio(s): 4.3:1
    Crawl ratio(s): 60:1
    Front axle/differential: GM Dana 60, Yukon 4340 chromoly axleshafts, Yukon manual hubs/4.56 gears, Detroit Electrac
    Rear axle/differential: 14-bolt, DIY4X disc brake kit/4.56 gears, Detroit NoSpin

    Front: Custom four-link, FOA 16-in-travel remote-reservoir coilovers, FOA 4-in-travel nitrogen bumpstops
    Rear: 63-in GM ¾-ton truck leaf springs, Pro Comp add-a-leaf, ORD 4-in Shackle Flip Kit, ORD 6-in SuperShackles
    Steering: PSC hydraulic-assist, ORD pitman arm, WFO Heavy-Duty Crossover Steering Kit, ORD tie-rod ends and drag link, custom tie rod, C&M Performance AMPCO bronze alloy kingpin bushings

    Tires: 37x12.50R16.5LT BFGoodrich Baja T/A
    Wheels: 16.5x9.75 Pro Comp Series 51, custom rock ring, Inner Air Lock beadlock

    Armor: Front winch bumper, custom rear bumper, custom rocker protection, custom T-case skidplate
    Cool stuff: Warn 8274 winch, custom fiberglass half-cab

    The front axle is a kingpin-style Dana 60, pirated from an ’83 Chevy K30 military ambulance, and it’s equipped with a Detroit Electrac locking differential, Precision Gear 4.56 gears, an eBay-sourced diff protector, Yukon 4340 chromoly axleshafts, and Yukon manual locking hubs. The axle is located laterally via a custom track bar made from 1.5-inch-diameter, 0.250-inch-wall material with Currie Johnny Joints at each end. The bar is affixed to custom mounts. The steering setup utilizes an Offroad Design pitman arm; WFO Concepts Heavy-Duty Crossover Steering Kit; C&M Performance Machine AMPCO bronze alloy kingpin bushings; ORD tie-rod ends; Offroad Design drag link; and custom tie rod made from 1.5-inch-diameter, 0.250-inch-wall tubing. A PSC ram-assist steering system makes pointing the big 37-inch tires a no-drama event.
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