Q: What is the role of the shock absorber?

A: Shock absorbers do not absorb shock; this is the role of the spring. The role of the shock absorber is to control the movement or oscillation of the spring, whether this is a coil, leaf or an air spring. The shock absorber provides a measured amount of resistance to control the spring. By doing this the shock absorber keeps the vehicles tyre in contact with the road surface.

Q: How do shock absorbers work?

A: Shock absorbers work by restricting the flow of oil through a series of valves, which are located in the piston & the bottom foot valve. There are a separate set of valves for compression & rebound. As the suspension movement increases stronger valves come into play to control the oscillation. This is known as multi stage valving. These valves provide the dampening for a shock absorber.

Q: How long will my shock absorbers last?

A: This is a hard question to give an exact answer to as there are many factors which can affect the life of a shock absorber:

  • Application – On highway or Off highway
  • Kilometers Traveled
  • Type of Suspension

Shock absorbers, like all truck components need to be replaced, gradual wear overtime might not be noticed until it is too late, and the shock fails completely. Some of these failures are internal and can’t be seen by a simple visual inspection. For this reason, as part of regular truck maintenance shock absorbers should be inspected and tested by a qualified service provider.

Q: How do I know when to replace my shock absorbers?

A: Signs to look for to when to replace your shock absorbers are as follows:

  • Irregular tyre wear – Scalloping or flat spots appearing on the tyre tread.
  • Unusual Handling or Braking- Vehicle kneeling into corners, loss of feeling of vehicle control or wheel chatter when braking.
  • Cracks developing on Axle Brackets & Body work.

Q: Can I test my shock absorbers by opening & closing them by hand?

A: This is an inaccurate way to test shock absorbers as you cannot replicate the forces of a heavy vehicle by hand. By pulling them in out by hand you are only using the first stages of the valving, where the oil is by passing the piston.

Q: How can I test my shock absorbers?

A: The easiest way to test your shock absorbers, whilst still fitted the vehicle is to use the Heat Test:

  1. After driving the vehicle for at least 30 to 60 minutes, touch each shock absorber on its body, after feeling the chassis for reference of temperature
  2. All shocks should be warmer than the chassis
  3. Different shock absorber temperatures from axle to axle do not indicate failures
  4. Varying temperatures on the same axle require further inspection.

A hot shock absorber is a working shock absorber!

Q: Should I replace a leaking shock absorber?

A: A leaking shock absorber should be replaced, as at some stage the top seal has been damaged. But do not confuse this with a misting shock absorber which is operating perfectly well.

A misting shock absorber looks similar to a leaking shock, but instead of large dribbles of oil on the body a misting shock will have a fine consistent layer of oil on the body. Approximately about two fingers in width at the top.

Misting occurs when heat is generated inside the shock absorber through friction. The oil becomes that hot it evaporates escaping the top seal, when it reaches the outside of the shock absorber which is much cooler the vapor cools on the body as a fine mist of oil. Do not be alarmed by this as the shock absorber is working fine & the top seal is being kept lubricated.

Q: Why does a shock absorber eventually fail?

A: Shock absorbers are consumables; they eventually have to be replaced. The oil breaks down because of heat, condensation & wear particles.

Under extreme conditions a shock can “boil off” the majority of its internal oil.  Lack of oil will cause lack of dampening.

Q: Do changes in ride height effect shock absorber performance?

A: Changing the ride height on your truck or trailer air suspension maybe a quick fix for a drive line angle issue or reaching a certain king pin height on a trailer. Unfortunately these changes will eventually lead to some expensive headaches in the future. Want to know more? Follow this link to read more on the topic.