how to change out a trailing arm

The nose dips, the front suspension abruptly compresses as the driver's head glances off the handlebar. Man meets handlebar as machine and rock meet with throttled energy.

The rear suspension snaps up inside the tunnel, sending sled and driver into an off-camber, sky-high hop. The driver tries to control his thoughts: what will hit first, rear axle or ski-tip?

Yet the bang keeps the sled roaring sky high. Something is going to break. It already has. Gravity overcomes horsepower and weight. The nose sharply dips, the driver leans back - arms stiffen on the handlebars - when the impact energy of three Minnesota Vikings' linemen on a Green Bay Packers quarterback unloads on the snowmobile's bulkhead.

Been there. Done that. Haven't we all?

The trailing arm

On January 6, 2001 American Snowmobiler held its third Powder Sled Playoffs in the mountains near Alpine, Wyoming. During this event, a test rider, aboard an 800 RMK, broke over a cornice, radically nose high, and dropped the right ski on a gator-sized rock. Rock 1, trailing arm 0.

Fortunately, Polaris built a crumple zone into its trailing arm. Meaning, when the front suspension receives a hard impact, the trailing arm will absorb the impact energy and bend outward (hopefully) as designed. This prevents the bulkhead and/or tunnel from bending, cracking or breaking in two. And we all know, trailing arms are cheaper to replace than a tunnel or bulkhead.

To keep the 800 RMK tracking down the trail, the test driver, who is also a Polaris dealership mechanic, rolled the RMK on its left side, removed the right ski and, using it as a hammer, whacked the trailing arm into alignment. It worked to get out of the hills, but the trailing arm was not perfect.

To round off this story, American Snowmobiler took the liberty of invading Tri-City Polaris (TCP), in Centerville, Utah, for the specifics on trailing arm replacement - and then some.

Dustin Francis, who has been twisting wrenches at TCP for seven years, has done his share of trailing arm swaps. For this "How To," we chose to install chromoly Holz trailing arms on a custom TCP-prepped 800 RMK.

These Holz arms are made from 4130 chromoly, which are oval shaped hollow tubes. According to Francis, the oval shape gives the arm added strength over that of a rectangular shaped trailing arm. Regardless, if installing an aftermarket trailing arm or an OEM trailing arm, our "How To" mechanic said two-hours are neeed for a complete swap-out and ski alignment. Not bad. Before moving on, consider purchasing or securing some snap ring pliers, a rubber mallet and an angle finder, these are the only speciality tools needed. Here are the steps.

1. Remove ski(s) and ski pivot bolt.

2. Remove stock spindle and steering arm.

3. Remove bolts that connect radius rods to trailing arm.

4. Remove lower shock bolt.

5. Pull trailing arm off of sway bar. When performing this task, save and reuse the nylon slider block held inside the OEM trailing arm.

6. Remove trailing arm mounting bolt from foot rest (toe-hold).

7. Using snap ring pliers, remove snap ring holding ball joint inside OEM trailing arm.

8. Knock out ball joint using a rubber mallet and an appropriate (matching sized) socket.

9. Install ball joint into trailing arm and reinstall snap ring, using snap ring pliers.

10. Tap in ball joint using the rubber mallet and socket.

11. Reinstall trailing arm at footrest with appropriate bolt and nut. Finger tighten, as the radius rod needs free movement until the radius rods are installed.

12. Spin stock radius rods off at the bulkhead and remove rods. (If installing aftermarket trailing arms and radius rods.)

13. Install new aftermarket rods, if needed.

14. Install new tie rod ends inside radius rods.

15. Run mounting bolts through the trailing arm and through the stock eyelet.

16. Set width with top and bottom radius rods. Twist and set to center.

Once the trailing arms are installed, take the necessary time to make ski alignment adjustments. Might as well, especially if the snowmobile is up on a jackstand.

Before moving on, let's discuss some alignment terms.

You've heard it: "This snowmobile tracks down the trail like it's on rails." What is the secret? We all know what it is like to drive a car or truck with a mis-aligned front end. Not only is it dangerous, but it flat out makes the ride stink.

Here are some definitions that will help brighten up the world of front suspension alignment.

Camber, positive or negative.

Imagine two posts standing side-by-side, equal distances apart with the tops slightly tipped into each other - this is positive camber. Tip the poles away from each other and this is negative camber. For best results, a snowmobile may like a slight positive camber (tip-in) one to three degrees. This allows the ski's inside edge to bite slightly allowing some aggressive turning.

To make camber adjustments do the following:
1. Insert a pipe (pipe outside diameter slightly smaller than the ski's mounting bracket inside diameter) through each ski mount until the pipe rests through mounting holes.

2. Lengthen or shorten the appropriate tie rods or radius rods until the desired setting is obtained. Check tip-in using a tool called an angle finder. It makes guessing a fact, not a guess.

Toe-in and toe-out

Pull the fence posts out of the ground and lay them on a flat surface parallel to each other, a foot apart. Tip each end in and this is toe-in; ends out - toe out. Optimum settings are 1/8-inch to 1/4-inch toe-out, never toe-in.

Correcting or adjusting toe-out is fairly easy to do. There are two ways, one is with the snowmobile on a jackstand (as we have here), the other is on a flat surface. If wanting to make adjustments on a the ground, jackstand, jump to the next subheading.

On the jackstand:

1. Position the handlebars straight.

2. If you notice the handlebars are not aligned straight, though the skis are pointed straight, do the following:

2A. Remove the skis and pivot bushings, depending on brand.

2B. Insert a pipe (pipe outside diameter slightly smaller than the ski's mounting bracket inside diameter) through each ski mount until the pipe rests through mounting holes.

2C. Make handlebar adjustments per the owner's manual or a shop's recommendations by adjusting steering arms and or radius rods.

2D. Remove pipe and reinstall skis.

3. Using a tape measure, measure the inside distance of the ski runners; take measurements at the front and back, not in the middle. Record the distances.

4. Consult your owner's manual for the correct toe-out spec for your particular model. As an example, to make a one-inch toe-out, rotate the tie-rod or radius rod equally, turn for turn, until the front ski runner distance is one inch greater than the rear.

5. Return snowmobile to ground.

On the ground:

1. Position the skis straight.

2. Lay a 10-foot long pipe, straight-edge or board next to the rear axle with the length running next to the ski's inside edge and beyond the ski hoop.

3. Using a tape measure, check the distance between the straight edge and the ski's inside edge. Take these measurements at the front and rear of the ski, not at the pivot point. If the measurements are equal, then zero toe-in/toe-out is present.

4. Consult your owner's manual for the correct toe-out spec for your particular model. As an example, to make a one-inch toe-out rotate the appropriate tie-rod or radius rod until the ski's inside front end moves one-half inch away from the straight edge; or in other words, is one-half inch greater in distance from the straight edge than that of the ski's back. Do the same on the other side. Two one-half inch adjustments will give the snowmobile a full one-inch toe-out.

With the new trailing arms installed, and camber and alignment adjustments made, the Polaris we worked on, with Tri-City Polaris' help, ran true and straight. Plus, the added benefit of Holz trailing arms gives a tricked-out rider a little more confidence as he hits the junk whoops on the trail.

For more information, contact Tri-City Polaris at 801/298-8081.