Why This M38 Is the Go-to Wheeling Rig for Mountain Adventures

The M38 military Jeep sitting in Simpson Offroad’s shop represents everything cool about building a proper trail rig. It’s a genuine military flat fender that’s been transformed into a serious mountain crawler while keeping its old-school soul intact.

What makes this build special is how it balances modern capability with period-correct aesthetics. The owner already had two other flat fenders built by Simpson Offroad with Kubota diesel swaps, but this M38 serves as his go-to wheeler for hitting the trails and exploring mountain terrain.

The heart of this rig pumps with a 231 Buick V6 paired to a T98 4 speed transmission and Dana 18 transfer case with a Warn overdrive unit. That’s old-school drivetrain gold right there! The Jeep already had some upgrades when it rolled into the shop: power brakes and a hydraulic slave cylinder, plus it was converted to hanging pedals and added a tilt column. The crossover steering setup uses a Saginaw box in manual configuration, though power steering remains a future possibility.

The real transformation happened underneath. Out went the original Dana 25 front axle and 401 rear, replaced with proper wheeling hardware. The front now sports an open knuckle Dana 30 with an Eaton E-Locker and 5.38 gears, while the rear features a ‘71 Dana 44 with flanged 30 spline axles, another E-Locker, and matching 5.38 gears. Both axles run Brembo disc brakes for serious stopping power on steep descents.

The fabrication work showcases real attention to detail. The custom swing-out spare tire carrier represents proper engineering - it uses 2"x4" 1/4" wall tube with a locking pin system that operates smoothly with one hand. The carrier bolts to both frame and bumper, allowing bumper removal without frame modifications. CJ body mount bushings eliminate rattling, while a high-lift jack mount with screw pins keeps everything secure on rough terrain.

Those rock sliders replaced basic angle iron pieces, providing real undercarriage protection. The full cage adds safety without compromising the classic flat fender profile. Moving the gas tank from under the seat to the rear compartment improves both safety and weight distribution.

Cooling presented unique challenges in the compact engine bay. The original setup used a sideways-mounted crossflow radiator with a poorly positioned fan. Simpson solved this with an Eastwood 22" tri-flow GM radiator mounted at a 30-45 degree angle, paired with their shroud and electric fan system. The temperature-controlled fan kicks in automatically around 155-165 degrees, with a manual override switch for added control.

The electrical system received serious attention too. A custom junction box mounted on the fender houses controllers for the electric fan and both E-Lockers. Separate bus bars provide constant 12V power, ground, and ignition-switched power - exactly what modern accessories require. Clean wiring makes future modifications simple.

The final touch involved swapping the original winch for a Warn 8274 with updated control box. These legendary winches remain the gold standard for serious recovery work, though mounting the newer control box required fabricating custom brackets for the hose clamps.

Simpson Offroad’s approach demonstrates how to modernize vintage iron without losing its character. The E-Lockers provide traction when needed, the disc brakes offer reliable stopping power, and the improved cooling system handles extended trail runs. Yet the rig maintains that classic flat fender aesthetic that turns heads at every trailhead.