Accessory drive belts and coolant hose replacements are perhaps the most popular and lucrative add-on services in the independent repair shop. Because belt and hose inspections are included in auto manufacturers’ scheduled maintenance charts, service writers at most well-managed shops recommend a belt and hose inspection along with tuneup, oil change, starting, charging, cooling, air conditioning and power steering system services. The potential exists with each belts and hose inspection to add an average of $100 or more in needed replacements to any service, whether it be a routine oil change or a complete engine replacement.

Most belts fail from a normal aging process, which means that the rubber in the belt eventually develops cracks that result in a broken belt. Some belts, such as the alternator belt and power steering belt, wear faster because they transmit high torque under specific driving conditions. The demands of increased torque subsequently cause higher operating temperatures that accelerate oxidation and wear. Other belts, such as an air injection pump or water pump belt, transmit very little torque and are, therefore, subject to very little wear.

Oil contamination is perhaps the major contributor to early belt failure because oil tends to deteriorate and lubricate the belt material, which, in turn, causes the belt to slip. Consequently, oil seal replacements often go hand-in-hand with belt replacements. One seldom-considered cause of belt wear and failure is a technician incorrectly replacing under-chassis splash shields. Of course, this neglect isn’t as much of a problem in metro areas as it is in rural areas, where the vehicle may be driven on sandy roads or through low-lying vegetation. In many cases, the failure to replace the front skid plate on a truck or SUV will result in sagebrush or other vegetation becoming entangled in the vehicle’s belt drive.

Failure Patterns in V-Belts
V-belts have specific failure patterns, the most common of which is a glazing condition caused by the belt slipping under load. Unlike serpentine belts equipped with automatic tensioners, V-belts require periodic adjustment to compensate for wear on the belt and pulleys. Prior to adjusting a V-belt, it’s important to determine if the belt is excessively cracked. If the belt is cracked, increasing belt tension will usually cause the belt to break, especially during high-speed driving or during heavy-load situations.

Next, because out-of-round or wobbling pulleys increase belt wear and reduce a belt’s torque-transmitting properties, the pulleys should be inspected for wear and concentricity. Since alternators are a high-torque accessory, alternator pulleys are usually the most prone to wear. If the alternator is a remanufactured unit equipped with a stamped-steel pulley, it should be inspected for concentricity and wobble.

Keeping in mind that a V-belt transmits torque through the sides or flanks of the belt, it’s important to examine those surfaces for oil contamination, glazing or wear. Remember that a V-belt will slip if the belt contacts the bottom of the V-pulley. In most cases, a new V-belt should fit near the top of its pulleys. If the belt is too wide, it will extend beyond the top of the pulleys. If the belt is too narrow, it will seat near the bottom of the pulley, which will cause the belt to have a very limited service life.

Last, some V-belts are prone to “rolling over” in their pulleys. In some cases, techs may damage the cord structure of the belt by prying it onto the pulleys, which can cause the belt to twist in the pulleys. In other cases, the pulleys may be misaligned. In rare cases, a long, unsupported span of V-belt can cause the belt to twist or roll over due to heavy torque loading or high-speed torsional vibrations from the engine’s crankshaft. In more common cases, a small pebble accidentally bounced from the road surface and lodged under the V-belt can twist or break the belt.

Seeking Serpentine Slippage
Serpentine or “flat” belts were created to reduce the overall length of an engine by reducing the number of drive belts. Up to four different belts and pulleys in a V-belt configuration, for example, have been reduced to a single belt on a serpentine configuration. In addition, the serpentine belt design lends itself well to automatic tensioning, and more frictional “wrap” around the driving and driven pulleys, all of which contribute to greater torque transmission capability.

In most applications, both the grooved and the flat sides of the belt are used for driving accessories. Because serpentine belts rarely slip, they may last up to twice as long as a typical V-belt configuration.

But serpentine belts can have excessive wear and slippage problems if their pulleys become misaligned or out of concentricity. Because the serpentine is a “flat” belt, alignment is critical. If, for example, a pulley is misaligned by a mere 1/16th of an inch, the load falls not on the center of the serpentine belt, but on the edge. To help alleviate alignment problems, auto manufacturers often alternate a V-groove pulley with a smooth pulley, which allows more side-to-side slippage.

In most cases, the serpentine belt, whether domestic or import, will fray on the edge because of incorrect load distribution caused by a misaligned pulley. An incorrect alternator or other belt-driven accessory replacement usually causes pulley misalignment. Asian imports, in particular, are subject to alternator pulley misalignments because of the vast number of substitute replacement alternator configurations available through the aftermarket.

In other misalignment cases, a technician may incorrectly install a mounting bracket or fail to check the hub height on a replacement part such as a water pump assembly. Most commonly, an accessory-mounting bracket may fatigue and break, which causes the pulley to tip inward and forces the belt to jump off the pulley under load.

An extremely accurate laser-beam tool is currently available in the aftermarket that will determine if an engine’s accessory drive pulleys are aligned correctly. Given some of the problems that can arise after a major engine service, the laser-beam alignment tool may well pay for itself very quickly, if it locates a pulley misalignment issue before the vehicle leaves the shop.

Having a Nose for Hose Repairs
Coolant hoses on late-model cars and trucks can be part of a very complex coolant distribution system. Some engine designs, for example, may conceal a number of specialized molded hose applications. Because engine compartment space is very limited, molded hose applications are becoming the rule rather than the exception on late-model imports and some domestics. These modern engines may, for example, have small coolant hoses leading to the throttle body, thermostatic fast idle devices, engine oil coolers and other coolant-related devices located in the engine compartment.

At present, most vehicle service schedules recommend a periodic inspection, rather than a specific replacement interval, for coolant hoses. Remember that most modern coolant hoses fail invisibly, from the inside out. The most visible failure indicator for hoses is cracking, swelling or ballooning of the hose itself at the water outlet connection of the engine. Large-diameter hoses, such as radiator hoses, can be pinched together by hand to test for sponginess or hardening.

The optimum time to recommend hose replacement is during any major engine service when hose accessibility is at its best. Otherwise, hose replacement can become a very costly, frustrating and time-consuming chore on many modern or compact vehicle engines.

In the end, a higher level of “belt and hose” awareness on the part of a shop’s service writer can create hundreds, perhaps thousands, of dollars of add-on sales each month, which should be the goal of any prosperous and progressive underhood shop. And, more importantly, addressing belts and hose maintenance may even keep your customers from being stranded on the side of the road.