Heavy Duty Trucking

NOV 2014

The Fleet Business Authority

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92 HDT • NOVEMBER 2014 www.truckinginfo.com fasteners, should also be regularly in- spected during preventive maintenance or annual inspections. There is virtually no standardization in air-spring mountings, even though only two manufacturers, Firestone and Goodyear, make most of them — a fact of life that irks Tomlinson. "It seems like every set is different," he said. "The bolt patterns change with the vehicle manufacturers, and are just enough different that you can't swap parts from one to another." He gets many of his parts from the TruckPro store in Greenwich, Ohio, where Jeremy Carruthers is the manager. "No, God no," he said when asked if there is any standardization. "You can have two trailers built side by side and they can have two kinds of air bags. There are 80 different part numbers carried just in this store. In front of me is a Firestone book that's got 150 pages of just air bags, with pictures, and there are four or five part numbers on each page. There are so many applications — drive axles on trucks, trailer axles, lift axles." Air springs cost from about $100 each for high-volume parts to $220 for more unusual types, he said. Of a predictable life cycle for them, Car- ruthers comments, "I wish there were an actual time line the guys could use before the bags blow up in their faces. But there are too many differ- ent uses. Normally, they replace 'em when they fail." ■ the short-haul trailer that the South Shore crew dealt with here, even if it sometimes goes on longer runs. This trailer is a 2000 Heil pneu- matic aluminum tanker that's been running "forever," he said. "The bags are probably the originals," and eventu- ally wear showed up that brought the trailer into the shop. Mechanics changed out all four bags because there was enough time. Sometimes a trailer must get back into service ASAP, so only one damaged or worn-out bag will be changed. There are many ways that rubber air bags can be damaged, and RP 643 lists five: ● Misalignment, where the upper and lower ends of the bag are out of line vertically. ● A loose girdle loop. ● Bottom-out abrasion, from the bag compressing too much. ● Over extension, from wheels dropping too low too many times. ● Circumferential cuts, from improper pressure or height adjust- ment. Cracks, holes, tears and chafing in the bags or at the top or bottom are among the types of damage that can occur. Cleaning the bags with a proper solution will give the mechanic a clear view of the rubber and other parts, the RP said. Other components, including the height adjustment and pressure limit- ing valves, air filter, and bushings and Suspensions Shocks Unpredictable, Too S hock absorbers are another wear item with a variable life span, unless one is established by a fleet. A set of shocks can be expected to run 150,000 miles in over- the-road service and 100,000 on vocational vehicles, said TMC's Recommended Practice 643. Product quality counts, of course, but the RP notes that shocks work harder with air- ride suspensions than old steel leaf-spring types, which were somewhat self-dampening. Shocks should be inspected at 15,000- and 50,000-mile PM intervals, unless service is more severe. Signs of damage or wear include dents and fluid leaks in and around the tubing, and worn bushings in mounting eyes. The "heat test," done soon after a vehicle comes in from the road, involves mea- suring or feeling for tempera- tures among the shocks in a suspension. If one is notice- ably warmer than the others, it might be defective, and should be removed for further inspection, the RP says. Turn the shock upside down and shake it while listening for any rattling that would indicate a broken internal part. Stroke the shock several times in a vertical position to determine if there's normal resistance. Compress it, then release the top; it should rebound quickly, and if not, it needs repairs or replacement. Tire cupping, vibration and rough ride – the latter two reported by drivers – are also signs of possible worn shock absorbers, and should be looked into. But cupping can also be caused by out-of- balance tires, loose suspen- sion components and axles that are out of alignment. Those are subjects unto themselves. The new air bag, near the bottom of the air suspension, almost shines. Al- though only two manufacturers make most air bags, bolt patterns for mounts are designed by vehicle builders and vary greatly. Kevin Tomlinson, South Shore's mainte- nance director, wishes an air bag replace- ment time could be predicted.

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