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1971 GMC K10 Rock Hound

Posted in Features on March 27, 2017
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Old iron is cool, there’s no arguing that. Metal dashes, bench seats, and a complete lack of electronic nannies are just a few of our favorite things about trucks from the 1970s. Kids these days, however, are more interested in adaptive cruise control that lets them text while driving—if they are even interested in trucks at all. Fortunately every rule has exceptions. Chris Sparks is a Millennial who has built an awesome 1971 GMC K10 at his shop Rock Hound Offroad in Grass Valley, California.

Wheeling a fullsize, longbed truck on trails like the Rubicon is tough without ending up with a truck that looks like a wrinkled beer can. Grumpy old guys like to say how kids don’t appreciate anything and have everything handed to them, but Chris has managed to keep his GMC pretty straight. He has no intention of shortening the longbed either. “I have to carry all of my friends’ gear on the trail since they drive little Jeeps and Toyotas!” he jokes.

When the factory 350 got tired, Chris Sparks swapped in a 5.3L Gen III engine with a Lunati Voodoo cam and ARP rod bolts. The engine breathes through an Airaid intake and exhales through modified Thorley headers and Flowmaster 50 Series mufflers. Chris used a wiring harness and unlocked ECU from Speed Scene and had Mark Romans at Motor Machine in Sacramento tune the engine. It makes 366 hp to the wheels, but like the rest of us Chris wants more power.

Tech Specs

1971 GMC K10
> Drivetrain
Engine: Chevrolet 5.3L V-8
Transmission: TH400 3-speed automatic
Transfer Case: Offroad Design NP203/NP205 Doubler
Front Axle: Torq Motorsports 14-bolt with 5.38 gears and ARB Air Locker
Rear Axle: Corporate 14-bolt with 5.38 gears and Grizzly Locker
> Suspension
Springs & Such: TK1 coilover air shocks and 3-link (front); 56-inch Chevy springs and Bilstein 5100 shocks (rear)
Tires & Wheels: 40x13.50R17 Goodyear Wrangler MT/Rs on Allied Rock-a-thon steel beadlocks
Steering: PSC steering box, hydraulic ram, pump, and reservoir, WFO steering arms
Lighting: Undead Offroad LED lights
Other Stuff: Griffin aluminum radiator, Airaid intake, Thorley headers, Flowmaster mufflers, Winters Sidewinder gated transmission shifter, Chevy Express bucket seats

Chris built the high-clearance front bumper out of 1.5x0.120-wall DOM tubing at his shop Rock Hound Off Road in Grass Valley, California. It currently holds four Apocalyptic LED lights from Undead Offroad, but a winch is on the top of the list of future upgrades.
Chris and his wife, Sienna, sit in bucket seats from a GMC Express van. He bought them out of the shed of an old hot rodder for $40 and reports that they are surprisingly comfortable. Auto Meter Phantom gauges monitor the vitals, and a Winters Sidewinder gated shifter rows the TH400 that was built by JR Transmissions in Auburn, California.
Lurking under the vintage sheetmetal is a thoroughly modern front axle built to withstand abuse under the heavy fullsize truck. The Torq Motorsports–fabricated housing uses a dropout third member that accepts 14-bolt gears. Chris runs 5.38s and a 40-spline ARB Air Locker with chromoly axles and Yukon Hardcore Locking Hubs. The Reid Racing knuckles have factory Spicer U-joints in them, which were intended to act as a fuse but have so far proven quite strong.
When he installed the 14-bolt front axle, Chris and his friend Alex Anderson replaced the leaf springs with aluminum coilover air shocks from TK1 Racing. The axle is located by a three-link that uses 1.5x0.250-wall DOM sleeved with 2x0.250-wall tubing for 1/2-inch-thick lower links fitted with 1 1/4-inch Ruff Stuff rod ends. The steering is all from PSC, including the pump, box, and ram.
The rear suspension uses 56-inch-long Chevy springs with Bilstein 5100 monotube shocks. They suspend a Corporate 14-bolt axle filled with 5.38 gears and a Grizzly Locker. The driveshafts were built by B&W Driveline. The rear is 3.5x0.120-wall tubing with 1350 U-joints and a CV at the T-case end. The front driveline uses a Toyota CV for increased angularity.
Gearing comes from an Offroad Design Doubler that mates a 2.0:1 NP203 low range to a 1.96:1 NP205 for a combined 3.92:1 low. Offroad Design’s twin-stick kit was used to allow for front-wheel drive, which is useful when maneuvering the longbed truck on tight trails. Chris built his own crossmember that ties into the link mounts to stiffen and strengthen the frame.
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