Stretch Belts In-Depth
Auto makers have consolidated accessory drive components onto one belt for the more than two decades. Stretch belts can take loads off of the main accessory belt drive, allow for better packaging, and solve NVH problems because less belt means less tension and fewer noise and vibration problems.
Application of Stretch Belts
If you see a belt on a late-model vehicle that does not have an automatic tensioner and runs between just two or three components, it’s probably a stretch belt. Some OE stretch belts will have the words “stretchy” or “stretch” written on the back.
GM started to use stretch belts to power the A/C compressor on 2009 models powered by the LS V8. Ford has been using stretch belts to turn the power steering pump on the 3.5L V6 since 2007. Ford also uses stretch belts to turn the camshaft-driven water pump on the 3.0L V6. Most import nameplate vehicles started using stretch belts in 2009, including Mazda, Subaru and Toyota.
Average Life of Stretch Belts
Stretch belts can last 100,000 miles or more, but this can vary dramatically depending on the vehicle’s environment and where it is mounted. This is why inspection is recommended; You cannot simply go by mileage recommendations.
When a stretch belt exceeds wear specifications, it’s no longer able to effectively grip the pulleys and will start slipping. The primary cause of slipping is material being removed from the belt’s grooves, not belt stretching. Over time, small debris and the interaction with the pulleys will wear the shoulders and valleys of the grooves.
When the grooves become too shallow, the pulleys bottom out. When this happens, the walls of the groove are no longer gripping the pulley. Inspecting the depths of the grooves is critical when determining when to replace belts. Always sell both belts together. Most serpentine belts wear at the same rate as stretch belts and have to be removed to service most stretch belts.
When inspecting a stretch belt, always measure the depth of the grooves with an inspection tool since the differences between a worn belt and a good belt can’t be seen or felt. The new materials used to make a stretch belt do not crack before the grooves are worn.
If you are removing an old stretch belt, cut it. If the belt is still in excellent shape, you can remove the belt with the correct belt tool in order to reach other components, but it’s highly recommended just to replace the belt if you don’t know the history.
Installation of Stretch Belts
Before ordering a new stretch belt, check the catalog for any additional parts like idler pulleys and special tools. These stretch belts have an elastic core that is designed to keep tension on the pulleys. Stretch belts are designed to stretch over one of the pulleys during installation, usually the crank or the largest pulley.
Never use a screwdriver or other sharp object to install the belt because if the belt is cut or the surface or grooves of the pulleys are damaged, the belt will eventually fail. Special tools are available from various tool and belt manufacturers that act as a ramp on the leading edge of the pulley. Some applications will require special tools to hold the belt on a pulley, like for the Subaru A/C compressor pulley.
Always follow the directions for proper tool placement and to determine the correct direction to turn the crankshaft.
After the belt is installed, always confirm the belt is in the grooves and re-check that there are no alignment problems.