GM SUV Adjustable Lowered Rear Trailing Arms

Installation Guide | Apoc Industries | Fits: Chevrolet Tahoe, GMC Yukon, Cadillac Escalade, Hummer H2, Chevrolet Avalanche

Overview

This guide covers the installation of Apoc Industries adjustable upper and lower rear trailing arms for GM SUVs. These arms are designed for lowered applications and allow you to correct pinion angle, restore proper axle position, and maintain correct suspension geometry after lowering. The installation process is the same across all covered years.

Pre-Install Checklist

Required Tools

• Floor jack and jack stands
• Torque wrench
• Torque angle gauge (required for 2007–2019 — these use torque-plus-angle specs)
• Socket set — metric and standard
• Digital angle finder or magnetic inclinometer
• Tape measure
• Grease gun
• Wheel chocks
• Safety glasses, gloves, and steel-toed boots (PPE)

Bushing Grease — Important

⚠ All Apoc Industries polyurethane bushings must be lubricated with silicone grease only. Never use petroleum-based grease on polyurethane bushings — petroleum grease will break down the polyurethane material and cause premature bushing failure. Grease all bushings thoroughly before and after installation.

Safety Warnings

⚠ Park on a level surface and chock the front wheels before lifting the vehicle. Always support the vehicle securely on jack stands. Never work under a vehicle supported only by a floor jack. Support the rear axle with a floor jack throughout the installation to prevent it from dropping when the arms are removed.

Critical Torque Note

⚠ Always final-torque all trailing arm bolts with the vehicle at ride height — full weight on the suspension. Torquing while the suspension is hanging will preload the bushings and cause premature failure.

Torque-to-Yield Note (2007–2019)

⚠ The 2007–2014 and 2015–2019 generations use a torque-plus-angle specification. First torque to the initial ft-lb value, then rotate the fastener an additional specified number of degrees using a torque angle gauge. A standard torque wrench alone is not sufficient for these years.

Arm Length Chart

Measurements are center-to-center between bolt holes. Set arms to the correct length for your drop height before installation.

Hardware Torque Reference

1999–2006

2007–2014

2015–2019

Always torque at ride height with full vehicle weight on the suspension.

Understanding Pinion Angle

Why Pinion Angle Matters

When you lower a vehicle, the rear axle moves upward relative to the frame, which changes the pinion angle. If left uncorrected, an improper pinion angle causes driveline vibration, accelerated U-joint wear, and poor driveshaft operating angles. Adjustable trailing arms allow you to correct this by repositioning the axle to restore proper geometry.

The goal is to keep the operating angle at each U-joint in the 1–3 degree range at normal ride height under the vehicle’s own weight. Most solid-axle GM SUVs leave the factory with approximately 1–3 degrees of nose-down pinion angle at static ride height — this small downward angle compensates for axle movement under acceleration.

How to Measure Pinion Angle

• Measure with the vehicle on level ground at normal ride height — full weight on the suspension, fuel tank reasonably full, no extra load
• Use a magnetic angle finder or digital inclinometer
• Measure the angle of the driveshaft
• Measure the angle of the pinion flange — place the tool on the flat face of the pinion yoke
• The difference between these two measurements is your true pinion angle
• Nose-down = positive number — the pinion is lower than the driveshaft centerline
• Target: 1–3 degrees nose-down at static ride height

Step-by-Step Installation Sequence

Step 1 — Prepare the Vehicle

• Park on a level surface and set the parking brake
• Chock the front wheels
• Raise the rear of the vehicle and support securely on jack stands under the frame
• Remove both rear wheels
• Place a floor jack under the rear axle to support it — do not allow the axle to drop freely when the arms are removed

Step 2 — Measure Stock Arms Before Removal

• Before removing anything, measure the center-to-center length of both the upper and lower stock trailing arms on each side
• Record these measurements — they are your baseline reference

Step 3 — Remove Stock Trailing Arms

• Remove the upper trailing arms first, then the lower arms
• Note the routing and orientation of any brake line, ABS sensor wire, or parking brake cable brackets attached to the arms before removal
• Retain the factory hardware — it will be reused unless new hardware was supplied with your kit

Step 4 — Set New Arm Lengths and Lubricate Bushings

• Set the new Apoc upper and lower arms to the correct center-to-center length for your drop height using the chart above
• Ensure equal thread engagement on both ends of each adjustable arm
• Leave the jam nuts slightly loose — final length verification happens after the vehicle is at ride height
• Lubricate all polyurethane bushings with silicone grease before installation — do not use petroleum-based grease

Step 5 — Install New Trailing Arms

• Install the lower trailing arms first, then the upper arms
• Re-attach any brake line, ABS sensor wire, or parking brake cable brackets in their original orientation — verify all lines and wires are clear of moving parts
• Hand-tighten all bolts at this stage — do not final torque yet

Step 6 — Reinstall Wheels and Lower to Ride Height

• Reinstall the rear wheels and torque lug nuts to factory spec
• Lower the vehicle to the ground so the full weight is on the suspension
• Roll the vehicle forward and backward a few feet and bounce the rear suspension to allow it to settle at true ride height

Step 7 — Verify Pinion Angle and Axle Position

With the vehicle at ride height, verify pinion angle and axle centering before final torque. Refer to the pinion angle section above for measurement instructions.

• Target 1–3 degrees nose-down pinion angle at static ride height
• Adjust the lower arms primarily to correct pinion angle and restore proper axle position
• Use the upper arms for fine-tuning axle centering and final pinion correction if needed
• Confirm the axle is centered side-to-side in the vehicle
• Once satisfied with the position, tighten the jam nuts firmly against the adjusters

Step 8 — Final Torque

With the vehicle at ride height and arm lengths confirmed, torque all bolts to the specifications for your year range listed above.

1999–2006 — standard torque wrench:

• Lower trailing arm bolts (frame and axle side): 111 ft-lbs (150 Nm)
• Upper trailing arm bolts (frame and axle side): 70 ft-lbs (95 Nm)

2007–2014 — torque-plus-angle (torque angle gauge required):

• All trailing arm bolts (upper and lower, frame and axle side): 74 ft-lbs (100 Nm) then rotate an additional 55 degrees

2015–2019 — torque-plus-angle (torque angle gauge required):

• All trailing arm bolts (upper and lower, frame and axle side): 74 ft-lbs (100 Nm) then rotate an additional 50 degrees

• Tighten all jam nuts securely against the adjusters
• Double-check that all brake lines, ABS wires, and parking brake cables are properly routed and clear of all moving parts
• Mark all torqued fasteners with a torque stripe for visual verification

Step 9 — Final Checks

• Re-check pinion angle after torquing to confirm nothing shifted
• Confirm the axle is centered side-to-side
• Cycle the suspension through full droop and compression to verify no binding or contact on any arm, bracket, line, or wire
• Reinstall any underbody shields that were removed
• A professional 4-wheel alignment is strongly recommended after installation

Post-Install Notes

• Re-check all fastener torque after 50–100 break-in miles
• Grease all arm bushing fittings at each oil change interval using silicone grease
• Inspect all hardware for loosening at each oil change interval
• If vibration is present after installation, verify driveshaft and pinion angles before assuming a driveline component issue
• Always use silicone grease on polyurethane bushings — petroleum-based grease will break down the polyurethane and cause premature failure

Safety Disclaimers

This installation guide is provided for reference purposes. Apoc Industries assumes no liability for improper installation, use of incorrect torque values, or failure to follow all safety procedures. Suspension modifications significantly affect vehicle handling characteristics. Always have suspension work inspected by a qualified mechanic and comply with all local laws regarding vehicle modifications and lift height limits.

Apoc Industries | apocindustries.com | Document Version: v1.0