Constant tension clamps maintain a more constant force using a spring. When the hose compresses, the spring closes the clamp tighter with very little loss of tension.
Fortunately, belts and hoses normally show signs of impending failure. Knowing what to look for during pre-trip inspections is critical to keeping ahead of trouble. Proper belt and hose maintenance falls into four basic steps:
- Buy only high-quality replacement parts that fit.
- Install properly, inspecting for and repairing problems that could doom your new parts.
- Re-tension belts and tighten hose clamps as necessary to prolong life.
- Inspect regularly and replace belts, hoses and clamps well before failure is likely.
Belt wear can be much more subtle than a big crack. “Check the sides and undersides of belts for glazing, excessive wear and cracks,” says Jim Grant of Trebar Kenworth Sales in Boise, Idaho.
Glazed belt sidewalls indicate slippage from too little tension, explains Ken Bridges, fleet and heavy-duty sales manager at Gates Corp. “Deep bottom cracks may result from high heat conditions in the engine compartment,” he says. “If the belt is falling apart in layers, it could be oil contaminated. Pitted or streaked sidewalls may result from a foreign object getting trapped between pulley and belt, or a rough pulley wall surface.”
Bridges adds: “The ribs of serpentine belts should be carefully checked for deep or excessive numbers of cracks. Gates engineers say that if there are more than three cracks per inch, 80 percent of the belt’s service life is gone.”
Frayed edges are also a sign of trouble, says Dan Swofford, an engineer at Freightliner Trucks.
Belt inspection should also include a tension check. Slipping is the most common cause of early failure because it means friction without lubrication.
Belts that are too tight or running on misaligned pulleys are the second and third most common causes of failure. So check alignment, too, in case a loose bolt or broken bracket has allowed an accessory to move.
Al Hertzog, director of the North American Institute, a training center for Volvo and Mack personnel, recommends using a belt tension gauge because of its accuracy. “You get 10 different tension readings if 10 different people adjust a belt,” he says.
Swofford says a rough guideline for checking tension without a gauge, such as during a pre-trip, is to push your finger into the center of the belt’s free span. If you can depress it much farther than its thickness in a short span, or twice its thickness in a span 2 feet or more, it’s probably too loose.
It’s a good idea to give even those automatically tensioned poly-vee belts a tension test with your thumb, suggest Peterbilt service managers Deuce Kaufman and Redmond David. A driver who stays familiar with his equipment will notice a reduction in tension, or even internal friction caused by a tensioner problem. Belt stretch or tensioner failure may be indicated by a mark on the tensioner that’s not between the two marks on the engine.
Experts stress choosing belts made by a reputable manufacturer and custom-designed for your application. You don’t necessarily have to buy the original equipment manufacturer belt, but you should get a solid indication that the belt was designed for your truck.
Hertzog mentions, for example, having the right cord structure and angle of the vee that match the pulley design. Here are three basic steps for replacement:
GET THE RIGHT PART. Take the time to loosen mounting bolts and move the accessory as far as needed for proper installation. Never pry a belt onto the pulley with a screwdriver to save time or to force a wrong belt to fit.
CHECK PARTS FOR PROPER ALIGNMENT. Bent or broken brackets, loose or missing bolts, or a replacement accessory or bracket that does not fit will leave pulleys misaligned. Misalignment creates abnormal stresses and generates extra heat. Hertzog recommends replacing multiple belts in properly matched, new sets.
TENSION THE BELT CORRECTLY. Do this at least twice: once at installation, and later after break-in. The belt will stretch a bit and also settle more fully into the vee.
Bridges recommends setting initial tension at the factory maximum, running the belt for 10 minutes, and then retensioning to the middle of the recommended range. Hertzog recommends retensioning after 3,000 miles. After break-in, check tension at about twice the oil change interval or as your owner’s manual recommends.
Peterbilt experts say that poly-vee belts and automatic tensioners were invented to handle the greatly increased torque required to drive late models’ cooling system parts. Because the tensioner also can suffer wear, it, too, should be checked. While the belt is off, rotate the tensioner back and forth. Any roughness indicates a worn bearing that will prevent the tensioner from keeping the belt in adjustment, Hertzog says. A bad tensioner can create a growl like a failing alternator bearing.
Swofford suggests checking this way: Mark the tensioner’s position. Then, using a breaker bar in the tensioner’s square hole, rotate it as if removing tension from an installed belt. Then release it. If the tensioner does not return to its original position, it should be replaced. If you inspect the tensioner often, you’ll note a decrease in its torque when it’s not functioning right. In that case, replacement is essential.
With the belt installed, make sure the mark on the tensioner sits between the marks on the part to which it is mounted. With automatic tensioners, a will-fit belt that’s the wrong length will show up as a tensioner mark outside the other two. Only if the marks line up properly will belt tension be correct.
The classic belt installation mistake, David says, is the tendency to think that if tight is good, tighter is better. Excessive tension causes damaging heat, he says. Belts are actually designed to slip around the pulleys very slightly. Failed A/C compressor and alternator bearings are typical results from over-tightened belts. Hertzog recalls two cases in which belts were so tight that a crankshaft upper bearing shell was ruined.
“Hoses should be firm with no soft spots or obvious damage, cracks running lengthwise, or bulges next to clamps,” says Grant of Trebar Kenworth.
David recommends squeezing the hose. “It should be resilient, not mushy,” he says. “Rubber that’s deteriorating loses its resiliency.”
Gates’ Bridges explains that coolant and other chemicals form a reaction that creates “micro-cracks in the hose tube, allowing the coolant to attack and weaken the hose.” This occurs only near the hose connections, so you need to check the hose with your fingers and thumb near the connections. If the middle is firm, but the ends are soft and mushy, the hose is being attacked in this manner and should be replaced.
Clamps, too, need a careful check. Constant torque clamps that use springs to hold the tension despite expansion and contraction are the best. Or use heat-sensitive thermoplastic band clamps, such as those made by Gates.
“All hose clamp adjusters lose torque after installation due to cold-flow of the hose material under the clamp,” Swofford says.
Truck manufacturers often specify a torque rating for hose clamps, so check your owner’s manual or even factory repair manuals. Get an inch-pound torque wrench and observe recommended torques. Specified re-torque done during routine inspections is lower than initial torque, Swofford says, because extra torque is used at installation to compensate for new hose crush.
Peterbilt experts recommend a careful look at hose routing. Extra clamps and fasteners installed in the middle between connections are often used to kill vibration or keep hoses from chafing. Even this hardware should be kept in good condition. The stakes are even higher with brake system air hoses, power steering hoses and, especially, fuel hoses that run near battery cables.
Hertzog points out the importance of coolant maintenance. Keep supplemental coolant additives at correct levels with traditional coolant, or use extended life coolant and keep it pure. The same calcium scale and other solids that interfere with cooling systems and water pumps will harden hoses and shorten their life, too.
Post-2002 engines require more frequent hose inspection. “We have had to design for very tough heat rejection problems,” Kaufman says. “We’re battling under-hood temperatures that are often 50 degrees higher than before.” As a result, David says, “We can’t recommend looking at the hoses at 50,000 miles any more.” Inspect at least at oil change intervals.
Swofford recommends replacing coolant and heater hoses as a complete set, as they tend to deteriorate at about the same rate. If you’ve had one fail, why risk a repeat?
Experts recommend putting the money out for high-quality hoses, especially if running a post-October 2002 engine with higher heat. Silicone hoses are becoming the high-quality standard, lasting considerably longer than standard hoses.
Gates’ Bridges recommends, instead, electrochemical-resistant EPDM hose, which “offers the same durability and performance as silicone in typical heavy-duty applications.” The problem with silicone is that it allows water to escape right through the hose, to the tune of gallons per year. If you regularly check antifreeze strength and adjust with a spectrometer, this won’t be an issue. But if you want the minimum of coolant maintenance, you might want to heed his advice.
Bridges says another problem is imperfect engine or radiator connections. “Fittings that are out of round or lack a full or partial interference bead tend to leak,” he says. “It is best if both fitting and hose are round, smooth, and free of seams or imperfections.” If necessary, replace components with irregular fittings.
Don’t use solvent to assemble hoses onto their connections because it will shorten hose life, David says. Rod Ward, director of sales engineering at Flexfab, agrees. “If the hose is difficult to install, lubricate with water or a mild soap and water solution.”
Install clamps around the hose first, unless you can open them completely, and install all the way onto the fitting. There may even be a stop point, intended for the end of the hose to rest against. If you install short of that point, the hose is likely to leak.
Normally a bead or thicker ring around the fitting helps hold the clamp and hose in place. “Always place the clamp behind and not over the bead,” Ward says. “The clamp should be located so that there is one bandwidth or a quarter-inch minimum of hose on the end and between the clamp and the bead. Feel for the bead under the hose to locate it if you can’t see it.”
Ward says Flexfab’s Duraguard Silicone hoses should be installed using worm gear clamps or constant torque stainless steel clamps. Initial torque should be 40 inch-pounds with care taken not to overtighten. Re-torque to only 20 inch-pounds.
Consult torque specifications for your truck maker or the part manufacturers if using different hose or clamps.
Regular attention to hose and belt condition means long life for these parts. With proper preventive maintenance, you can avoid downtime by replacing them before they fail.