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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) – PSC Certified Refurbished

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

$600.00
$1,150.00 $600.00
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Part Number: SD-SG400R

If you're tired of fighting your Wrangler through rocks, ruts, and tight trails, this upgrade gives your steering system the strength the factory box never had.

These are PSC BIG BORE XD® Steering Gear Conversion Kits for 2003-2006 Jeep TJ and LJ Wranglers, offered as PSC Certified Refurbished units.

Each unit has been inspected, rebuilt where needed, and tested to meet our performance standards. They may show minor cosmetic wear from prior use or handling, but they are fully functional and built to perform the same as our standard units.

The factory Mercedes ZF steering gear used in 2003-2006 TJ and LJ models was never designed for the demands of larger tires, lockers, and aggressive off-road use. With its smaller piston and lighter-duty construction, it can struggle when the trail gets serious.

The BIG BORE XD® Conversion replaces the factory gear with a heavy-duty Saginaw-style steering box featuring a larger piston for increased steering power and durability. It also includes provisions for PSC Cylinder Assist®, giving you a clear upgrade path if you decide to add even more steering capability later.

This conversion is designed for Jeep owners who want a tougher steering foundation that can handle real-world trail abuse and larger tire combinations with greater confidence.

Because this is a conversion, installation is more involved than a standard steering box replacement. Additional hoses are required, steering shaft modifications may be needed, and some applications may require a 1-inch body lift for clearance.

If your factory steering gear is worn out or struggling to keep up with your build, this is a proven way to upgrade to a stronger, more capable steering system without buying new.

All refurbished unit sales are final.

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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 
  • Vehicles 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