Straight Talk About Alignment
By: Tom Berg
Truck pulling to one side? Tire tread wearing unevenly? Buying new tires and just want to be sure you get all the tread life you’re paying for? Then you know it’s time for a frontend alignment.
But there’s more to it than watching the technician run the rig onto a rack, set up the laser boxes and adjust things so the red beams hit the bulls-eyes on the targets. If he’s a good man who works at a good shop, he’ll check out all the parts that make up what we call the front end. What are they?
The Technology & Maintenance Council of ATA (703-838-1763) has an entire recommended practice RP 642 on Total Vehicle Alignment. The RP notes that it’s not just the front end, but other axles and components on the truck or tractor, that need attention during the alignment process.
Irregular tread wear on steer-axle tires may be caused by faults in the front end, or by misalignment elsewhere on the chassis. A rear axle sitting out-of-square with the frame is one possibility; another is maladjusted wheel bearings on the steer or rear axle(s).
Alignment is no simple matter. The RP includes 14 appendices and several check lists. These discuss basic terminology, plus the proper way to inspect steering gear, wheels and wheel bearings, U-bolts and other axle and suspension fasteners. Most of these take a trained eye to inspect, but almost anyone can see if something’s amiss with the tires.
First, tire inflation: Air pressure that’s too low or too high can quickly destroy tires, and adversely affect alignment. Most drivers check pressure by kicking or thumping, but tests show that most guys cannot feel or hear a soft tire until it’s down by 30 or more psi (where 100 psimight be normal). At that point it might as well be flat. You need to "stick" each tire with a gauge at least once a week, inflate all tires that are not up to the proper pressure, and arrange repairs for those that are habitually low.
Then comes tire matching: Are the duals on rear axles, and the two tires on the steer axle, really matched? Are both or all tires on an axle of the same size, height and tread type? If possible, they should also be of the same brand because they’ll work well together.
Correcting inflation and matching problems may relieve some symptoms of misalignment, and may eliminate the need for a visit to the alignment shop. But if a visit is still indicated, it helps to know what the alignment specialist is supposed to do.
Guess what? Checking tire pressure is the first thing, according to RP 642. If he doesn’t bother, that could be your cue to go elsewhere, because he’s likely to skip other steps, too.
Take road tests, for example. This is where he compares your complaints (or your boss’) with what his trained hands and posterior can feel as the truck goes down the road. For instance, vibrations can come from various sources, and his experience can quickly isolate them. He’s supposed to road test the truck before and after inspection and repair/adjustment work.
Appendix 12 of the RP lists 10 additional steps, most with multiple points. These include inspection of steering gear (for signs of looseness and wear), brake drums (for centering), wheel bearings (endplay), wheel and tire runout (do they spin “true” with no more than 1/8-inch of wobble?), tire mounting (any high or low areas around the bead?), vehicle ride height (usually involving the air-ride suspension), and height of the axle spindles (uneven heights can come from wear, damage, mismatched tires and other causes).
Keep some of these in mind as you watch the tech go about his work. If he conscientiously prowls around the vehicle’s underside, eyeballing and grabbing the above items and more all before he starts using his fancy laser apparatus chances are you’re getting your money’s worth.
Just remember, it’s not only the front end we’re concerned about.
Article provided by: http://www.retread.org This article, by Tom Berg, Equipment Editor at roadSTAR, July 2003 is used with permission.)
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