Ram 3500 Trailing Arms Upgrade — Weld-On Kit Install Guide

Axle wrap and wheel hop are the most common complaints on lifted Ram 2500 and 3500 trucks running lift blocks in the rear. The Core 4x4 universal trailing arm kit solves both by tying the rear axle directly to the frame with a pair of heavy-duty 7075 aluminum arms. This guide walks through the full weld-on install on a 2008 Ram 3500 Mega Cab, including axle bracket placement, stitch welding technique, frame-side mounting, and working around the fuel tank on the driver’s side.

Fitment: Universal kit — installed here on a 2008 Ram 3500 Mega Cab with lift blocks in the rear

Why Trailing Arms on a Lifted Ram 3500

Lifted trucks with rear lift blocks put significantly more torque on the axle during acceleration and towing. The block raises the spring perch, increasing the lever arm between the axle centerline and the spring mount. That extra leverage allows the axle to rotate under load — a problem called axle wrap. The result is wheel hop, driveline vibrations, and premature wear on u-joints and pinion seals.

Trailing arms prevent axle wrap by connecting the rear axle directly to the frame. They hold the axle in position under acceleration and braking, keeping the pinion angle consistent and eliminating the hop that comes from the axle oscillating against the leaf springs. On a truck like this Ram 3500 — a manual transmission with low gearing — the problem is even worse because the clutch dumps torque into the drivetrain without a torque converter to absorb the shock.

What Is in the Universal Trailing Arm Kit

The Core 4x4 universal trailing arm kit includes:

• Two trailing arms — 2” 7075 aluminum tubing, approximately 60” eye-to-eye at minimum adjustment, extending to about 62”
• Axle brackets — quarter-plate steel, weld-on, double-shear design
• Frame brackets — quarter-plate steel, weld-on with optional bolt-through holes
• FK Massive rod ends — no lubrication or maintenance required, made in the USA, 3” diameter
• Misalignment spacers — sized for different frame widths (2-5/8” on this Ram application)
• Weld spacers — protect the rod end bores during welding
• All mounting hardware — 3/4” bolts and jam nuts

Why 7075 Aluminum Arms?

The arms are built from 7075 aluminum because it has a memory that steel does not. If you clip a rock on the trail, a 7075 aluminum arm will flex and return to shape. A steel trailing arm in the same situation bends permanently and needs to be replaced. For a set-it-and-forget-it part that lives under a truck, that durability matters.

Step 1: Axle Bracket Placement

The axle brackets mount to the bottom of the rear axle tube, positioned directly below the frame rail. Alignment between the axle brackets and the frame is important because the frame-side brackets sandwich the frame — there is no left-to-right adjustment once they are welded.

Measuring and Marking

1. Use a plumb bob (or laser) to drop a reference line from the inside edge of the frame rail down to the axle. Mark both sides.
2. Measure from the backing plate to each mark to verify centering. On this truck, the passenger side measured 8-3/4” and the driver side measured 8-1/2”, so Spence split the difference at 8-5/8”.
3. Account for bump stops: The factory bump stop adds about 3/16” to the effective frame width. Use the outside edge of the bump stop as your reference and offset accordingly.
4. Position the bracket straight down on the bottom of the axle tube, between the u-bolt and the shock mount.

Step 2: Prep and Stitch Weld the Axle Brackets

Before welding, there are three critical rules Spence follows:

Welding Rules for Axle Brackets

1. Disconnect the battery before any welding. You are putting electrical current through the frame, body, and axle. Failing to disconnect risks shorting out electrical components.
2. Stitch weld and alternate sides. Do about 1-1/2” beads, then move to the other side. Use a wet rag to cool the axle between passes. Continuous welding risks warping the axle tube and melting axle seals.
3. Weld the inside first, then the outside. Inside welds pull the bracket tabs inward toward the joint bore. Finishing with outside welds pulls that pressure back out, leaving the bore at the correct dimension. If you weld outside first, the bracket clamps down on the rod end bore so tightly that you will struggle to install the arm and may damage the paint.

Use the weld spacers. Spence initially welded with the FK rod ends still in the brackets and got slag all over the joint surfaces. The kit includes weld spacers specifically to protect the bores during welding. Swap the rod ends out for the spacers before you strike an arc.

Ground Placement

Since you are welding on the axle, ground your welder directly to the axle — not the frame. Spence cleaned a spot on the bottom of the shock mount for the ground clamp. Touch it up with rattle-can primer when you are done.

Step 3: Paint the Axle Brackets

After welding both axle brackets, clean up the welds with a flap disc and apply rust protection immediately. Spence used Dupli-Color Rust Barrier, which is designed to spray directly onto rusty or bare metal automotive parts. POR-15 is another solid option for underbody work. Follow the rust barrier with a coat of black rattle-can to match the undercarriage.

Step 4: Frame Bracket Placement (Passenger Side)

The frame brackets sandwich the frame rail and weld to the outside surface. Each bracket has two holes on top for optional bolt-through mounting, but Spence uses those as plug weld holes for a permanent connection.

Setting the Length

The trailing arms adjust from about 60-1/4” to 62” bolt-to-bolt. Spence targets 61 inches — the middle of the adjustment range — to leave thread engagement in both directions. To set this:

1. Measure from the center of the axle bracket bolt to where the center of the frame bracket bolt will land.
2. If measuring alone, account for the bolt head width (1-1/8” on these 3/4” bolts). Half of that — 9/16” — is the offset from the outside of the bolt head to center.
3. Mark the frame rail at the target distance (61” on this truck).

Vertical Positioning

The FK rod ends are 3” in diameter, which means you need at least 1-1/2” between the bottom of the frame rail and the center of the bolt hole. Spence placed the bracket approximately 1-1/2” from the top of the frame rail, giving a quarter-inch clearance between the rod end and the frame while keeping ground clearance as tight as possible.

Welding the Frame Brackets

Weld the outside surfaces only — do not weld the inside of the frame. Inside welds pull the bracket tabs inward and make it difficult to mount the arm. The outside beads plus plug welds through the top holes provide more than enough strength for this application. Clamp the bracket flush to the frame before welding.

Step 5: Driver-Side Frame Bracket (Working Around the Fuel Tank)

On this 2008 Ram 3500 Mega Cab, the driver-side fuel tank sits directly over the frame bracket location. The tank needs to come down enough to access the frame rail for prep and welding.

Dropping the Fuel Tank

1. Support the tank with a transmission jack. Center it under the tank before loosening anything.
2. Remove the two straps. All fuel connections are at the rear of the tank.
3. Lower the front end first. Spence initially tried lowering just the front, but needed more clearance for prep work. He ended up lowering the entire tank by recentering the transmission jack and bringing it all down.
4. Move the fuel lines up and out of the way. Secure them so they do not contact the welding area.
5. Watch for diesel seepage from the breather area. The customer dropped this truck off with a near-full tank, which made the job heavier and messier.

Tip: For mockup and prep, Spence measured the passenger-side bracket position relative to the body mount crossmember support on the frame (7-1/2” from the closest corner). He transferred that measurement to the driver side, verified with a tape measure to confirm the 61” arm length, and then committed to the weld.

Welding Near the Fuel Tank

With the fuel tank lowered, Spence was able to weld the outside of the frame bracket normally. The backside was tighter with fuel lines nearby and some diesel seepage from the breather. He welded as much as he was comfortable with — good beads on three sides — and noted that even that reduced amount is more than sufficient for a double-shear trailing arm bracket. Many trailing arm setups use single-shear mounts; this double-shear design is inherently stronger.

Step 6: Install the Trailing Arms

With all four brackets welded, painted, and dried, the arms bolt in:

1. Insert the arm into the axle bracket with the rod end seated in the bore.
2. Install the 3/4” bolt through the bracket and rod end with the appropriate misalignment spacers.
3. Repeat at the frame bracket.
4. Adjust arm length to the target distance (61” on this install) using the threaded rod end.
5. Tighten jam nuts once the length is set.

Spence noted that the 61” target worked well — the arms had most of their adjustment threaded in, which maximizes thread engagement and strength. Both arms matched, confirming that the bracket placement measurements were accurate.

Driver-Side Notes: Is It Really That Hard?

The fuel tank detour adds time, but Spence found the driver side was not as bad as he expected. The transmission jack was the key tool — it held the tank safely out of the way without disconnecting fuel lines at the rear. On this 2008 Mega Cab with the tank mounted close to the frame, the bolt-on frame bracket option might have worked depending on clearance, but the weld-on approach guaranteed a clean install on both sides.

Time and Tools

Tools Required

• MIG welder (ground to axle for axle brackets, ground to frame for frame brackets)
• Angle grinder with flap disc (weld cleanup)
• Plumb bob or laser level (bracket alignment)
• Tape measure
• Transmission jack (driver-side fuel tank)
• Socket set and impact gun
• Clamps (holding frame brackets flush)
• Dupli-Color Rust Barrier or POR-15 (rust protection)
• Black rattle-can paint
• Wet rags (cooling axle between weld passes)
• Safety glasses and welding hood

Frequently Asked Questions

Products Featured in This Install

Related Content

• Ram 3500 Track Bar & End Links Install — the next video in this build series covering front sway bar end links and adjustable track bar
• Ram 3500 Steering Kit Install
• Ram 3500 Long Arm Kit Install
• Why You Need Control Arms — educational overview of control arm geometry

Fitment: Universal trailing arm kit — adaptable to multiple truck platforms. Installed here on a 2008 Ram 3500 Mega Cab. Questions about this kit: sales@core4x4.com | (385) 375-2104