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Your go-to tractor, trailer suspension inspection and maintenance guide

Legally, you are required to inspect your tractor and trailer suspension systems annually, but running a safe and productive fleet demands more than a once-a-year suspension check.

Jason Morgan is the editor of Fleet Equipment. He has more than 14 years of B2B journalism experience covering the likes of trucking and construction equipment, real estate, movies and craft beer industries.

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“We cannot overstate the importance of the daily, visual pre-trip inspection to help identify any potential concerns that may need to be addressed,” said Bill Hicks, SAF product manager with SAF-Holland. “This inspection helps to identify issues such as loose fasteners and worn components. The more severe the application, the more frequently the inspections should take place.”

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If your drivers and technicians are visually inspecting your suspensions, they have to know what to look for and what it means for the repair. 

Quick disclaimer! Your specific tractor and trailer manufacturers, and your suspension supplier, are the first line of suspension maintenance. Check with them for the proper repair procedures. It’s advice we followed ourselves. That’s why we reached out to a bevy of suspension experts to pull together general rules of thumb that would give you guidance in your suspension inspections. Here’s what they said.

Leaf spring suspensions

Sure, leaf spring suspensions typically require less maintenance than air spring suspensions, but to think it’s set-it-and-forget-it equipment is a mistake. Make sure your drivers and techs are giving these a good look. 

What are they looking for?

“Fasteners and bushings are the most important items to check on leaf spring suspensions,” said Tyler Bernens, senior suspension product manager for Meritor. “Loose fasteners that are allowed to operate for any period of time will result in irreversible damage. Fastener torque should be checked periodically, especially U-bolts.”

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“That’s the first thing: Check the torque on the U-bolts that fasten the spring pack to the axle,” agreed Chuck Boden, technical support specialist with Link Mfg. “The U-bolts often loosen over time and, when they do, allow the axle and the spring to move independently of one another, instead of functioning as a unified system.”

“Most manufacturers recommend rechecking fastener torques 500 miles after repairs,” Bernens added. “Similarly worn bushings that are not replaced will put excess stress on other components, leading to more extensive damage.”

Doubling down on the importance of bolt torque, Adam Kuiken, validation engineering and warranty manager for Reyco Granning, said, “Bolt torque, especially related to the clamp group and pivot points, is important to check. For example, the clamp group between the spring and axle must,” he stressed, “be torqued within 3,000 miles of being put into service.”

From there, Link’s Boden pointed to pins and bushings. 

“Pins should be greased periodically and bushings inspected for wear,” he said. “Spacers and shackles need to be checked and if loose, the spacers need to be replaced. Spring packs should be regularly inspected for fatigued, broken or cracked leaves. Alignment of the leaves in the spring pack is also important and if misaligned, the centering pin may be to blame.”

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To name a few more, Hendrickson’s Melanie Elliott, marketing manager, and John Knutson, technical services manager, rattled off a couple often-overlooked leaf suspension bullet points:

  • Shocks. Look for leaking, misting, broken, missing/loose fasteners.
  • Control rods. Look for split, torn, or shredded bushings and/or missing fasteners.
  • Hangers/hanger pins. Look for cracking, movement or wear.
  • Spring seats. Look for cracking or signs of looseness. “This would indicate insufficient U-bolt torque,” they noted.

Air spring suspensions

Here are the top three maintenance trouble spots courtesy of Link Mfg.’s Boden:

  • The air spring;
  • The air valve; and
  • The shock absorber.

“Things like bushings are way down at the bottom of the list,” he said, noting that this is due to the complications airbags can present. “The air spring is constructed of a metal bead plate on top, the rubber bellows, or air bladder, in the middle and the metal pedestal at the bottom. The rubber portion of the air spring is often referred to as the air bag by technicians. The integrity of the exterior rubber can most often become compromised by direct contact with a foreign object, excessive mechanical fatigue, high stress or through simple wear and tear.”

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Let’s dive into the inspection details.

 1. Air springs

“Since the air spring is pressurized, visually inspect to ensure nothing rubs against the air cell, which could lead to damage,” SAF-Holland’s Hicks said. “The life of an air spring will vary depending on the type of application. Off-road applications will typically wear out faster than on-highway applications. Therefore, it is important to keep the air spring and lower piston clean of debris, using a mild soap and water solution.

“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.”

Large cracks and splits in the rubber will all be readily apparent.

“Road debris, improper ride height and worn shocks can lead to damaged air springs,” Meritor’s Bernens noted. “Check air springs for punctures from road debris, abrasions or internal blind nut punctures. If an air spring has been over extended or suffered a blind nut puncture, then inspect that the vehicle is set for the correct ride height.”

You’ll need to take the overall lifecycle into account as well.

“Over time, the rubber bellows can lose its elastomeric qualities and may start deteriorating,” Boden said. “Exposure to high temperatures can also cause the rubber material to age prematurely. Older air springs can also exhibit weather checking, also referred to as dry rot, and the evidence for this looks like small, fine cracks on the surface of the air bag.”

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 2: Air valves

Boden noted that contaminants like moisture or oil that have entered the system are a top cause of air valve malfunctions. If present, you’ll notice a sticky resident inside the air-handling components.

“The use of air driers in the system can help alleviate the problem with moisture and I would recommend this, particularly for those vehicles that frequently experience changes in climate,” Boden said. “Technicians should look at ride height for indicators of a malfunctioning valve. If the ride height is too high, the valve may not be exhausting air from the bladder properly. If the ride height is too low, the valve may not be admitting air into the bladder.”

3: Shock absorbers

When it comes to air spring suspension shock absorbers, SAF-Holland’s Hicks stressed: “Visually inspect the shock absorbers at least weekly. The visual inspection allows you to easily see when a shock is leaking.”

“Worn out shocks will lead to increased wear on other components to include the air spring. Regularly check the shock to make sure that it is preforming its function,” Meritor’s Bernens said.

“Use caution,” Hicks warned. “The lower shock body could be hot when touching it after the trailer has been operating.”

Your productive shock mileage my vary, but Link’s Boden noted that you should expect to replace shocks approximately every 100,000 miles. Hicks added that the shock absorbers will wear out before typical rolling lobe air springs. 

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4: Bushings and beyond

Don’t forget the small stuff, or it can haunt you.

“Replace worn bushings immediately to prevent damage to other components,” Bernens said. “Improper pivot bolt torque will lead to damage to adjacent components. Always ensure your pivot bolts are torqued to the manufacturers’ specifications.”

Hicks noted that required bushing maintenance can vary depending on application. 

“For instance,” he said, “the front pivot connection bushings are critical to the life of the suspension. The pivot fastener must provide sufficient clamp load through the bushing to prevent premature bushing and/or bushing core failure. Therefore, it is a good practice to re-torque the pivot connections every time you do a routine brake job, or every 50,000 to 100,000 miles. In severe-duty applications, where brake jobs are performed more frequently, it is important to check torque more often.”

Click here to read how suspension maintenance differs with tractors and trailers.

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