Complete Ball Joint Kit - Knurled

Synergy Jeep JK / JKU Adjustable Ball Joint Kit

Part #: 4127XX
Weight: 5.8 lbs
  • MSRP: $360.00
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After 5 years of development and over 100,000 test miles our Heavy Duty Adjustable Jeep JK Ball Joints are here! This is the last set of ball joints you will ever have to buy. Limited Lifetime Warranty. Tighten up your steering for good with our patent-pending (# 16/020894) design which is fully adjustable, serviceable, and rebuildable without having to press the ball joints back out of the axle end forging yokes (C's). These ball joints never have to come back out. Available in knurled and non-knurled versions to fit all vehicles regardless of what type of ball joints were installed previously. Lower ball joint bearing surfaces are CNC machined from 4140 steel, heat treated, induction hardened, and ferritic nitrocarburized to make these the longest lasting, longest wearing ball joints on the market. Kit includes all 4 ball joints to service one Jeep and the adjuster tool for adjusting the preload on the lower ball joints.


  • 07-18 Jeep Wrangler JK/JKU


  • Tightens sloppy steering
  • Designed to last the life of the vehicle
  • Never need to replace ball joints again
  • Best in class price/performance ratio
  • Limited Lifetime Warranty


  • Kit includes all 4 ball joints and lower ball joint adjuster tool
  • Patent Pending lower ball joints are adjustable so they always have the correct amount of preload
  • Knurled and non-knurled ball joint housing options to fit any vehicle
  • Lower ball joints are rebuildable on the vehicle without removal
  • Lower Ball Joint bearing surfaces are CNC machined from 4140 steel, heat treated, induction hardened, and ferritic nitrocarburized for extreme wear resistance
  • Low profile dust boots are made from thick nitrobutile rubber (NBR) to protect the joint from contaminants and eliminate any chance of tearing
  • Zerk fittings included for trouble-free maintenance


  • Synergy 4119 High Performance Grease recommended
  • Knurled ball joints required when replacing knurled ball joints that have enlarged the axle end forging bores
  • Non-Knurled ball joints recommended for replacing non-knurled ball joints
  • Due to these ball joints being tight tolerance, metal on metal ball joints, proper fitment is critical. Using the wrong style of ball joints can cause significant steering issues. We always recommend installing non-knurled ball joints until non-knurled ball joints are no longer a press fit into the axle end forging bores. If your axle end forging bores have been enlarged to the point that non-knurled ball joints are no longer a press fit, knurled ball joints are required.
  • Use of the improper ball joint style for the axle housing voids our lifetime warranty. It is up to the installer to verify the proper ball joint style is being used.
  • Compatible with RCV axle shafts
  • Rebuild Kits and Replacement Parts Available Here.

Limited Lifetime Warranty: 
For the original purchaser, this warranty covers defects in materials or workmanship of the ball joint for the lifetime of the joint. Ball Joints are wear items and normal wear of the ball joint is not subject to this Limited Lifetime Warranty. The wear items of the ball joint will periodically need to be replaced once the adjustment in the joint is used up and are available separately as a ball joint rebuild kit. Length of time between rebuilds is subject to the use and build of the vehicle.

Installation Instructions

Part #Description
4127Jeep JK 07-18 HD Adjustable Ball Joint Kit, Non-Knurled
4127KNJeep JK 07-18 HD Adjustable Ball Joint Kit, Knurled

    • SKU
    • Weight
      5.8 lbs
  • Ball Joint Kit (Review the Notes section for whether you need knurled or non-knurled)
    Non-Knurled, Knurled
  • Add Chassis & Bearing Grease
    No, Yes, SKU: 4119

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