Trailing Arm Fix Short Cuts

By: Ray Sala - 5/5/02

Fixing the Coil-Sprung Mitsubishi Montero Trailing Arm
before it breaks on the trail

Applicable Vehicles: Only v6 Gen 1 & Gen 2 Montero's come with trailing arms and coil sprung rear suspensions. Gen I 2.6L 4 cylinder Montero's, and 3.0L v6 Gen II Montero sports come with leaf sprung rear ends, so they don't have trailing arms.

What Does the Trailing Arm Do?
Image courtesy of Ray Sala
This drawing shows the physics behind the trailing arm.

The main purpose for the trailing arms in a coil sprung suspension is to hold the rear axle perpendicular to the drive shaft at all times and throughout the full cycle of the suspensions travel. Without the trailing arms, the axles could easily move forward or backwards which would damage the drive shaft and certainly prevent a vehicle from going any further without undertaking immediate repairs.

Why does it break?

Image courtesy of Ray Sala
The achilles heel of the Montero

It's been postulated that the cause of a recent rise in Trailing Arm failures may possibly be directly related to the number of owners who are removing rear anti-sway bars to increase articulation; putting larger wheel's and tires on our 4x4's and driving them under conditions which puts the articulation of the rear suspension under some extreme angles.

By having one tire down, and the other up, this twisting motion may be putting forces on the trailing arm, which are beyond its original design specifications.

An Ounce of Prevention...

So how can a Mitsubishi 4x4 owner prevent trailing arms from failing on their rigs? Using the diagram above, you can easily see where your trailing arm may break under the conditions described above. Welding a piece of 1/4" thick steel through the weak area seems to effectively prevent this problem. Here are some pics of my rig being temporarily fixed on the trail, followed by pictures of the reinforcements.

Image courtesy of Ray Sala Image courtesy of Ray Sala
Trailside fixes like this can be prevented This picture clearly shows where the arm failed
Image courtesy of Ray Sala Image courtesy of Ray Sala
The new "fishplate" in place on the arm It is barely noticeable under the truck

The first image has the reinforcement "illuminated" and the second shows the same image as viewed normally.

Disclaimer: Making modifications to your vehicle may make your vehicle less reliable and potentially more dangerous.ORN is not liable for any effects caused by these modifications. Owners attempting these modifications do so at their own risk.

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