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John Retzloff: 1977 GMC K15

Posted in Top Truck Challenge: 2011 on November 1, 2011
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Photographers: Sean P. Holman

Truck class: If At First You Don’t Succeed
After trying for years to get into TTC, John Retzloff finally got the call-up as an 11th-hour alternate in the Truck Class. His GMC K15 certainly has the clearance for big obstacles like the Mini-Rubicon, and the bed dimensions for narrow squeezes like the Twister. It also boasts a host of owner-fabbed metalwork including the bumpers, sliders, and rear stinger.

The GMC now runs on a 117-inch wheelbase after the front axle was relocated five inches forward, and the bed was narrowed to a 48-inch width for easier access to tight trails. Rolling stock comprises 53-inch 16R20 Goodyears wrapped around 20-inch Velocity eight-spoke rims, and a Warn 9500ti in on tap for those times when forward progress is temporarily halted.

The Details

  • Owner name/city: John Retzloff/Covelo, CA
  • Occupation: Diesel mechanic/heavy equipment operator
  • Vehicle model: 1977 GMC K15
  • Estimated value: $30,000
  • Engine/aspiration: Propane-injected 454ci GM Mark IV V-8, Summit racing headers, 2½-in exhaust
  • Transmission: SM465
  • Transfer case: Custom-built dual NP205s
  • Suspension (f/r): 52-in GM rear leaf springs, Rancho RS9000 shocks/63-in GM rear leaf springs, shackle drop, Pro Comp MX-6 shocks
  • Axles (f/r): Dana 60/GM 14-bolt
  • Axle ratio: 4.88:1
  • Wheels: 20-in Velocity aluminum eight-spoke
  • Tires: 53/16R20 Goodyear AT2A

John Retzloff, Team #44

  • Most looking forward to: “Probably the Tank Trap. Despite five-foot-deep water and poison oak, I love wheeling in ravines.”
  • Not looking forward to: “The Mini-Rubicon. If the Warthog rolled it two or three times in the middle, I know I have my work cut out for me.”
  • Playing on his iPod/CD player right now? “Alice in Chains’ Live, or Z-Rock 106.7 on the radio.”

In the back, 63-inch GM rear leaf springs with an overload leaf incorporate a shackle drop to suspend the GM 14-bolt, which is fortified by a Detroit Locker, Superior shafts and 4.88:1 gears. Twelve-inch-travel Pro Comp MX-6 shocks dampen the ride, and dual custom owner-fabbed NP205 transfer cases send torque to the 14-bolt via a driveshaft outfitted with a 1480 U-joint. Bed and bodyside sheetmetal have been sacrificed to clear the 53-inch tires, and a High-Angle parking brake has been swapped in too, just in case the rear drums start to fade.
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