Synergy 4127 HD Adjustable Ball Joint Kit for 07-18 Jeep Wrangler JK/JKU/WJ

Vehicle Fitment

• 2007-2018 Jeep Wrangler JK/JKU (Sport, Sahara, Rubicon, Unlimited, etc.; 2-door & 4-door; 4WD)
• 1999-2004 Jeep Grand Cherokee WJ (Laredo, Limited, Overland; 4WD)

Fitment Notes

• Kit includes 2x upper and 2x lower adjustable ball joints with adjuster wrench
• Available in non-knurled (standard axles) or knurled (for enlarged axle bores)
• No pressing out of axle tubes required--serviceable while installed
• Greaseable zerks included; recommended to use Synergy 4119 high-performance grease

Features

• CNC-machined 4140 steel bearing surfaces, heat-treated and nitrocarburized
• Lower joints are adjustable and rebuildable in-vehicle for preload tuning
• Heavy-duty 4140 steel studs and low-profile NBR dust boots
• Serviceable without axle disassembly--press-in once, adjust for life
• Compatible with RCV axles and aftermarket shafts
• Limited lifetime warranty supports durability and rebuildability
• Includes tool for setting preload and zerk fittings for maintenance

Specifications

• Part Number: 4127 (non-knurled); 4127KN (knurled)
• Application: Upper & lower front ball joints, greasable
• Material: 4140 steel bearing race, durable heat-treated studs
• Warranty: Limited lifetime (heavy duty parts) / 12-month (hard parts)

Included Components

• 2x Upper HD ball joints
• 2x Adjustable lower HD ball joints
• 1x Ball joint hardware kit
• 1x Adjustment wrench
• 4x Grease zerks

Product Description

The Synergy 4127 HD Adjustable Ball Joint Kit upgrades the front steering on Jeep Wrangler JK/JKU (2007-2018) and Grand Cherokee WJ (1999-2004) models with heavy-duty, rebuildable joints. Both upper and lower joints are machined from 4140 steel, fully greaseable, and heat-treated for longevity.

A patent-pending adjustable lower joint allows in-vehicle preload tuning without removal, dramatically improving steering precision. The kit installs with a one-time press fit, includes knurled or non-knurled options, a wrench for adjustment, hardware, and grease zerks. Backed by a limited lifetime warranty, it's an excellent upgrade for lifted or daily-driven Jeeps seeking durability and performance.