UMI Performance 2039-R Adjustable Rear Lower Control Arm with Roto-Joint Technology

The UMI Performance 2039-R is an on-car adjustable rear lower control arm engineered for street performance and enthusiast-level driving. Constructed from 1.250" x 0.120" DOM mild steel tubing with a TIG-welded 4140 chromoly tube adapter, this control arm delivers superior strength and durability over factory rubber or polyurethane bushing alternatives. A brilliant, long-lasting powder coat finish protects against corrosion and wear. The arm ships fully assembled and ready to install using OEM hardware.

Roto-Joint Technology:

At the heart of this control arm is UMI's proprietary Swivel Roto-Joint — a rotational spherical pivot designed to allow 28 degrees of total unrestricted movement, eliminating suspension bind for precise, low-friction operation. The Roto-Joint features a 4140 chromoly hard chrome-plated spherical ball rotating within a CNC-machined Delrin race. Delrin is chosen for its exceptional wear resistance, tensile strength, and dimensional stability. Unlike rubber or polyurethane bushings that deflect under load, the Roto-Joint's non-deflecting design improves traction and significantly reduces wheel hop.

This control arm uses a hybrid bushing configuration: a polyurethane bushing on the chassis-side mount to absorb road noise and vibration before it enters the cabin, and the Roto-Joint on the rear-end side for bind-free articulation. Both ends are greaseable and low-maintenance, making this an ideal setup for daily-driven performance vehicles.

On-Car Adjustability:

The arm features a chromoly heat-treated adjuster that allows length adjustment while the arm remains installed on the vehicle. This makes it easy to reposition the rear axle fore or aft — critical for fitting larger tires in the fender wells and for centering aftermarket rear ends to prevent tire rub.

Chrome Moly Upgrade Option:

A Chrome Moly variant is also available, constructed from 1.250" x 0.095" 4130 Chrome Moly steel, offering increased strength at reduced weight compared to the standard DOM mild steel version.

Key Features:

• Constructed from 1.250" x 0.120" DOM mild steel tubing (standard) or 1.250" x 0.095" 4130 Chrome Moly (upgrade)
• TIG-welded 4140 chromoly tube adapters
• Swivel Roto-Joint with 28° of total unrestricted movement
• 4140 chromoly hard chrome-plated spherical ball in CNC-machined Delrin race
• Hybrid design: polyurethane bushing (chassis side) + Roto-Joint (axle side)
• On-car adjustable via chromoly heat-treated adjuster
• All joints greaseable and fully rebuildable
• Durable powder coat finish
• Uses OEM hardware
• Ships fully assembled — no additional prep required

Optional Spanner Wrench: UMI offers an optional spanner wrench for adjusting and disassembling the Roto-Joint. As the Delrin race wears over time, the spanner wrench is used to tighten the adjuster ring to restore tension, or to fully disassemble the joint for cleaning, inspection, and rebuilding.

The UMI Performance 2039-R rear lower control arm is an ideal upgrade for street performance builds requiring precise rear suspension geometry, reduced wheel hop, and the flexibility to accommodate larger tires or aftermarket rear axle assemblies.