How to Inspect Trailer Suspensions

Trailers suffer from a chronic lack of attention. They may not see a technician for months on end if they run from drop yard to drop yard. When one of these lost souls appears in the yard, it probably needs a little attention.

The first step in keeping the equipment rolling is to check the driver vehicle inspection reports for write-ups, and then do a thorough visual inspection to ensure it is fully operational, ensuring it is visually free of any obvious signs of failure in any major component.

The visual inspection should include:

• Inspecting the air springs for damage or wear
• Inspecting pivot bushings for signs of excessive wear
• Looking for movement around bolted connections that can suggest loosening
• Checking control valves for damage or abnormal leakage
• Checking shock absorbers for leaking or mounting issues

That's stuff every driver should be doing every day, but it never hurts to look a trailer over before getting into a serious inspection. Chances are if nothing untoward is seen with a thorough visual inspection, you might let it go until next time -- unless you have technicians standing around with nothing to do.

Mechanical Suspensions

Simpler in design and easier to inspect, mechanical suspensions don't hide their secrets well. When something is loose or broken, it's easy to spot when you know what to look for:

• The U-bolts holding the springs to the axles can work loose, so carefully inspect them, looking for signs of movement or loose nuts. Retorque as required to manufacturer's specifications. Check the center equalizer bolts, the torque arms (both fixed and adjustable), and the spring retainer hold-down bolts.
• Check the spring hangers and hanger pins, looking for cracks, excess movement, or wear. "This would indicate insufficient U-bolt torque," notes Howard Adkins, manager of trailer technical services at Hendrickson.
• Check the spring packs for loose or cracked springs and be sure no damaged or broken section of a spring leaf is loose or has separated from the pack. Movement of the spring leaves is also a symptom of loose U-bolts.
• On suspensions with control rods, inspect the bushings for wear and damage, bearing in mind they may be out of view. "Use a flashlight to closely inspect bushings and rubber parts looking for chaffing, wear, and permanent core displacement," advises Tony Ryan, national fleet service manager at SAF-Holland Americas. "Bushings typically are concealed within brackets or other mounting structures making them difficult to see. In addition to visual inspection, bushing wear can be determined by driver feedback, such as comments about chucking, pulling, or ride harshness.

Air Suspensions

Air suspensions are more complex that mechanical suspension, and have more wear parts like bushings, air springs, shock absorbers, and air controls that require inspection and periodic servicing.

"No system is maintenance-free, and in terms of air suspensions, it is important to pay attention to a few critical areas like correct ride height settings and the condition of the air springs, pivot arm bushings and height control valves." cautions Adkins. He advises the following checks:

• Since the air spring is pressurized, visually inspect to ensure nothing rubs against the air cell, which could lead to damage. Periodically check for road gravel or other abrasive debris between the cell and the piston and the bead plates. Removing the debris will help to prevent air cell abrasion and premature failure. Also, look for damage to the bellows or piston or misalignment of the mountings.
• Visually inspect the shock absorbers at least weekly. The visual inspection allows you to easily see when a shock is leaking. You can also check the shock by touching the lower shock body after the trailer has been operating. Use caution as the shock body could be hot. If it is warm, the shock should be functioning properly. A leaking shock is not an out-of-service issue, but it can lead to reduced service life and/or increased tire wear and ride quality issues.

Bushing maintenance requirements may vary depending upon the manufacturer and application, so always default to the maker's recommendations.

For SAF Holland suspensions, for instance, the front pivot connection bushings are critical to the life of the suspension, Ryan says. "The pivot fastener must provide sufficient clamp load through the bushing to prevent premature bushing and/or bushing core failure.

"SAF trailer air ride suspensions utilize a shear bolt front pivot connection design. This connection doesn’t require a torque check. Simply, visually inspect the bolt for any signs of movement at every routine maintenance check. DO NOT apply anti-seize compound or additional lubricant to pivot connection hardware. This can lead to unpredictable clamp loads and unreliable axle alignment," Ryan adds.

According to Hendrickson's Adkins, "Hendrickson air suspensions do not require periodic maintenance, but regular inspections are recommended, including, ensure that the ride height setting is correct, the air springs are not damaged or worn, and the pivot bushings do not show signs of excessive wear."

Related Inspection Items

While you're at it, you might as well check a few other components to make sure they're OK, too.

The trailer bogey alignment is a good place to start. That's because it's easy to do a quick down and dirty alignment check on trailer bogeys while you have the trailer in the shop. Ensure the front trailer axle is perpendicular to the body of the trailer by drawing a cord, secured around the trailer king pin to an identical point on each side of the front axle. The measurement should be exactly the same.

Check axle parallelism by measuring the distance from the center of one axle hub to the other. The measurement should be exactly the same on both sides. If a discrepancy exists, the trailer bogies may be out of alignment.

This can cause handling issues and will lead to premature tire wear on both the tractor and the trailer. It's a five-minute check that could save thousands of dollars.

Next, take a minute and look over the trailer bogey slider mechanism. It's a good idea to to do this because drivers find it very frustrating if they are unable to release or relock the trailer bogey slider mechanism. These sometimes seize up through lack of use or can be damaged by overly aggressive drivers. Check they are functioning properly and the locking mechanism is in good working order.

"A successful maintenance program ensures that the vehicle is operating at its optimum efficiency and ensures safety to itself and the public that shares the roads and highways during its transport," says Adkins.

"The successful maintenance program will often identify defects, which are prevented from surfacing in the first place, before a catastrophic incident, accident or violation can occur."

In other words, look after your equipment, and it will look after you.