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  • Angled front view of a silver PSC steering gear showing bronze input shaft, black anodized top cap, and precision port fittings.
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BIG BORE XD® Steering Gear Conversion - Jeep TJ / LJ (2003-2006)

BIG BORE XD® Steering Gear Conversion - Jeep TJ / LJ (2003-2006)

$1,150.00
$1,150.00
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Part Number: SG400R

The factory Mercedes ZF box on ’03–’06 TJ/LJ Wranglers? Weak. Small piston, thin case, and a bad habit of giving up when you add bigger tires or a locker. The BIG BORE XD Conversion Gear fixes all that with a Saginaw-style box, a bigger piston for more torque, and ports for Cylinder Assist when you’re ready to step up.

This isn’t a quick swap—it’s a proper conversion. You’ll need the right hoses, maybe a little steering shaft work, and in some cases a 1" body lift for clearance. But once it’s in, you’ll have a steering gear that can handle real trail abuse without crying uncle.

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About:About:

Why you’ll love it

  • Stronger Saginaw design – replaces the failure-prone ZF box
  • Bigger piston = more torque – turns big tires without a fight
  • Cylinder Assist ready – ports are machined into the case, not welded
  • Billet aluminum top and end caps – built for strength and serviceability
  • 14:1 ratio, 3.25 turns lock-to-lock – quick response without twitchy road manners

Tech InfoTech Info

Heads‑up for installers

  • This is a conversion. It’s not a 30-minute swap. Plan for hoses, shaft mods, and maybe a body lift.
  • Hose kit required: Use PSC HK2000 Hose Conversion Kit for a clean install.
  • Intermediate shaft: Factory shaft usually needs to be shortened ~2". Or install Jeep/MOPAR PN 52078705.
  • Clearance: Some rigs need a 1" body lift to clear the bigger gear and lines.
  • Ports: Metric O-ring, machined for -6 AN fittings to Cylinder Assist®. No welded junk here. 
  • Fluid: PSC recommends PSC 715 for best performance and component life.

Fitment

  • 2003–2006 Jeep Wrangler TJ & LJ
  • Replaces factory Mercedes ZF steering gear
  • Requires PSC hose kit and possible steering shaft modification

Use it with

  • PSC HK2000 Hose Conversion Kit
  • PSC High-Flow Pump Kit (don’t starve the gear)
  • PSC Cylinder Assist Kit (if you’re running 37s+ or hardcore trails)
  • PSC Cooler and Inline Filter for system longevity

Ideal for

  • TJ/LJ on 35s–40s 
  • Rigs with front lockers or heavy bumpers/winch setups
  • Builders planning for Cylinder Assist® down the road 
  • Anyone tired of blowing up ZF boxes

Specs

  • Gear Type: Saginaw-style conversion
  • Ratio: 14:1 (3.25 turns lock-to-lock)
  • Input Shaft: 3/4" – 30 spline
  • Ports: Metric O-ring, machined for -6 AN assist fittings
  • Mounting: 3-bolt, inside-the-frame
  • Covers: Billet aluminum top and end caps
  • Assist Ports: Threaded directly into housing (serviceable, no welds)

What’s included

  • BIG BORE XD Steering Gear (SG400R)
  • Pre-machined assist ports

Not Included: Hose kit (HK2000), intermediate shaft, fluid, fittings, or body lift components.

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Install Instructions

California Prop 65 Warning

California Prop 65 Warning

This product can expose you to chemicals including lead and di (2-ethylhexyl) phthalate, which are known to the State of California to cause cancer, birth defects or other reproductive harm.

For more information, go to www.P65Warnings.ca.gov