Fasteners – over torque or never torque

Fasteners can undergo severe conditions and need to be treated with care to ensure they don’t get damaged.

When servicing trucks and trailers it is becoming increasingly evident that fasteners are often subjected to two extremes – either over-torqued or not torqued at all.

Either of these situations will result in the same outcome: fasteners not doing what they are designed to do. So, why does this happen, and how can it be addressed?

Some suspension fasteners that need be checked regularly are in awkward positions, making them difficult for technicians to access. Added to this is the high torque that many of these fasteners require.

The process of looking up the correct torque specification, setting the torque wrench, crawling underneath the truck or trailer, and then reefing on the torque wrench to get a series of fasteners up to specification can be quite a task. Taking the option of leaving it alone if it looks tight can seem to be an appealing option. Especially so if the technician doesn’t see any immediate benefit for this extra effort.

On the other hand, using a rattle gun to check torque is very convenient but inherently flawed. There is no way of telling if the fasteners have been over-tightened. Some technicians have been known to run a torque wrench over the bolts after using a rattle gun, to check if they are tight enough.

Unfortunately, unless the bolts move when using the torque wrench, there is no way of knowing how much torque has been applied and they may have been tightened past the bolt’s yield point.

Unfortunately, neither of these two options provide any assurance that the fasteners will still be in place by the next service inspection. Components like axle U-bolts, pivot bolts and shock bolts will give a little over time because they are exposed to regular shock stresses.

Not checking these components for correct torque at regular intervals will result in components working their way loose. It will simply be a matter of time before this becomes evident and causes damage, such as elongated suspension hanger pivot holes or broken shock bolts.

Either case will result in failure and consequent damage to related components. Depending on which part fails, it could also result in a truck or trailer being out of service and off the road until repairs are carried out.

Hendrickson and most other suspension manufacturers provide a schedule outlining which fasteners should be checked for proper tension and how frequently this should be done. While checking the torque of these critical fasteners takes time and effort, it ultimately saves on vehicle downtime and costly repairs by preventing fastener failures down the line.