By Jeff Barker
Axle assemblies see the most abuse and are often the most neglected, especially when it comes to alignments. Too often tires are dragged over curbs in tight turning situations. Over time, that results in alignment problems. Axles that are out of alignment create rolling resistance, which causes a loss in fuel mileage and decreased tire life.
All over the place?
There are numerous indicators of trailer alignment problems. The most common is obvious when you're driving in the center of the lane and look in the mirror to see the trailer tandems off to one side of the lane – often referred to as dog tracking. Another indicator is unusually rapid tire wear.
When doing your pre-trip inspection, make it a point to stand by the left front and right front corners of the trailer and look at the sidewalls of the tires on either side.
Do the sidewalls appear to be straight in line with each other and with the sides of the trailer? If not, take a tape measure and check the distance between the rearmost edge of the wheel on the front axle and the forward most edge of the wheel on the rear axle on each side.
If the measurements are different, there's an alignment problem and the trailer should be taken to a shop to be checked out. Do not take these measurements between the tread of the tires themselves as any differences in tread depth will result in an inaccurate measurement.
If the outer wheels on your trailer look straight with each other on one side, and one or both wheels on the opposite side do not, that could be a sign of either a wheel bearing problem or a bent axle. Get this checked out before you move the trailer.
Getting in line
It's best to have a reputable, properly equipped shop do your alignment work. Here's what will take place:
Before the axle alignment is done, the axle center line must be checked. Refer to E in the diagram. If the axle(s) are more than 1/8-inch off center, that problem must be corrected before an alignment is performed. That may entail replacing worn suspension bushings.
Once the center line measurement checks out OK, measure the distance from the kingpin to the center of each end of the front axle. Refer to A and B in the diagram. After the front axle is properly aligned and there's no signs of axle damage or worn bushings, the distance from the front axle to the rear axle (C and D) is measured.
On most trailers with air-ride suspension, the alignment is adjusted by loosening the pivot bushing bolt and turning an egg-shaped cam adjuster in a frame-mounted hanger to move one end of the axle until the aforementioned measurements are correct. Then the bolt is retorqued.
Common spring-ride trailers have torque arms that hold the axles in line with the trailer's frame. The torque arms on one side of each axle are length-adjustable for alignment purposes. After the collar bolts on each end are loosened up, the threaded center section is turned to either lengthen or shorten the torque arm until it's lined up correctly; then the bolts are retorqued.
If your trailer was ever involved in a serious accident and the frame or subframe was damaged, it's important to replace those defective items. Some shops will try to cut corners by heating those items with a torch and straightening them, but that weakens the metal. Frame bolts and U-bolts should never be reused under any circumstances, which is important to remember if you ever need to deal with an insurance claims adjuster to get your trailer repaired.
Many van type trailers and some flatbeds have sliding tandem axle subframes. In some cases, the bogey rails (which are attached to the cross members with the evenly spaced holes that the slider pins lock into) can also be installed out of line with the trailer and cause an alignment problem. Also, if those holes are elongated and/or the slider pins are worn, the subframe can cause the trailer to dog track to one side.
It's important to check wheel end bearings on trailers. If your trailer has hub oilers, remove the rubber plug on each axle end during your pre-trip inspection. Check the oil level in the hub window and dip a clean finger into the oil. If it comes out clean with no metal shavings or signs of water in the hub oil (as in no abnormally light cream color in the oil), you're good to go. Otherwise, metal shavings and/or a plastic hub window that appears to be pushed out like a convex mirror indicate you have a wheel bearing problem.
Water in the oil? Get the hubs drained, cleaned, and refilled with new oil. If the hubs are grease-packed, the hubs need to be checked en route. If they're too hot to keep a hand on them right after you stop, get it checked out as soon as possible to avoid costly axle damage. On all trailers, keep a close eye on those wheel seals. If they're leaking, that's another sign of a possible wheel bearing problem.LL
Send any questions or comments regarding transportation law to:
Jeff McConnell and
James Mennella, Road Law, 3441 W. Memorial, Suite 4, Oklahoma City,
OK 73134, call 405-242-2030,
fax 405-242-2040, or e-mail