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Regularly Scheduled Shock Maintenance Doesn't Cost In The Long Run - It Saves!
Like most other chassis components, a program of regular scheduled maintenance for shock absorbers will help to avoid unscheduled down time and reduce overall maintenance costs.
The role of a shock has changed dramatically. Not so many years ago, most suspensions had heavy multi-leaf springs with limited travel and a great deal of inherent friction. These suspensions quickly self dampened and therefore limited the amount of work the shock needed to perform.
Low friction suspensions such as air and taper leaf have dramatically changed the shock's role. Shocks now play a critical role in dampening suspension oscillation.
Properly functioning shocks can help reduce the wear of more expensive suspension components such as air bags, while assisting in the reduction of tire wear and vibration damage to the cab and chassis. They also aid in reducing driver fatigue. Worn shocks simply cannot assist in providing control over today's sophisticated suspension systems.
When Should Shocks Be Replaced?
There are many tell tale signs that indicate it may be time to replace shocks.
Inspect for:
- Uneven Tire Wear - Balance should be checked first
- Ride Deterioration
- Excess Vibration
- Sagging Taper Leaf Springs - This is not caused by weak shocks
- Premature wear on cab, electrical, and cooling system components
- Broken or Torn Air Springs - Shocks will only affect this if they are broken or are missing
Leaking VS. Misting Shocks
Misting shocks are often mis-diagnosed as failures. Misting is the process whereby very small amounts of shock  fluid evaporate at high operating temperatures through the upper seal of the shock. When the "mist" reaches the cooler outside air, it condenses and forms a film on the outside of the shock body. When mixed with road debris and dust, a grime will often coat the entire body of the shock. Misting is a perfectly normal and necessary function of the shock. The fluid which evaporates through the seal area helps to lubricate and prolong the life of the seal.
Many technicians find it difficult to differentiate between a misting shock and a true leaker which needs to be replaced. A leaker will show clear signs of fluid leaking in streams from the upper seal. These streams can most easily be seen when the shock is fully extended, and one inspects as far up the main body of the shock (underneath the dust cover or tube) as possible.
Take The Heat Test
Shock absorbers function at temperatures ranging from ambient to 3500F. A shock's role is to dampen the oscillation of the truck's springs. It does this by transforming the energy produced by the spring to heat and dissipating it. As a result the shock should be slightly warm to hot to the touch after normal use.
If ride deterioration is experienced and there is suspicion that a shock has failed internally, which is visually undetectable, perform the following "SHOCK HEAT TEST" within a few minutes of operating the equipment:
- Drive the vehicle at moderate speeds for at least 15 minutes.
- Within a few minutes of driving the vehicle, touch each shock absorber carefully on its body below the dust cover or tube, after first touching a nearby part of the chassis to establish a reference ambient temperature of the metal.
- All shock absorbers should be warmer than the chassis. Suspect a failure in any shock that is noticeably cooler than its mate on the other end of the axle. Different temperatures from axle to axle do not indicate failures, but cooler temperatures on any one axle does warrant removal and examination of the cooler shock absorber.
- To inspect for an internal failure, remove and shake the suspected shock. Listen for the sound of metal parts rattling inside. Rattling of metal parts can indicate that the shock has an internal failure.
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This documentation was provided by Gabriel.
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