How to: Maintain a fifth wheel

| December 12, 2008

Jost also is working to minimize grease waste, but is taking a slightly different approach, says Rich Carroll, vice president of sales and marketing. Jost is developing Lubetronic, based on a small lubricant cartridge fitted with an electric motor that is used in Europe. At set intervals, the device automatically delivers a tiny amount of grease to the fifth wheel’s jaws and locking mechanism. Those are the only parts “that will need to be coated to maximize their longevity,” Carroll says.

Still, most operators use standard models, requiring top plate grease once a week or every 3,000 miles – more with intense drop-and-hook uses – and jaw lubrication every 30,000 to 60,000 miles, depending on manufacturers’ recommendations.

Plenty of fifth wheel-specific lubricants are available, but high-quality chassis grease remains the most popular and economical product for top-plate lubrication, at least in regions where the ambient temperature remains above 0 degrees Fahrenheit. In colder conditions, heavy gear oil works better. Some truck owners use synthetic lubes, but Fontaine’s Brown says that can pose problems for truckers who regularly switch trailers.

“Unless you’re using the same grease for all your equipment, you could run into compatibility issues,” he says. Some mineral-based lubricants won’t mix well with synthetics, Brown says. “When that happens, the products degrade and form a gumlike substance that’s very tough to remove.”

Beyond lubrication, fifth wheels last longer if they’re not abused. Careless truckers have been known to squeeze their rigs under fully loaded trailers, then slam into the kingpin. Actions such as these accelerate wear and can damage tractor and trailer parts.

Longevity also is affected by application. Off-highway duty will dramatically trim life expectancy, as will construction work – particularly tip-trailer operations – and city work involving constant dropping and hooking.

Before fifth wheels wear out, though, they can be adjusted to tighten the slack that comes with use. When that fails to correct the problem, they can be rebuilt with kits.

The steps for rebuilding vary by brand, model and type of kit. Complete instructions are packaged with the kits and are normally available online at the manufacturers’ websites. None of these jobs is technically difficult, usually entailing fewer than a dozen parts. The biggest challenge for most people will be the removal of their fifth wheels, unwieldy slabs of iron weighing upward of 300 pounds. Jost models, though, can be rebuilt while attached to the truck.

The best way to avoid, or at least delay, the cost and effort of such tasks is with regular, thorough inspections and proper lubrication. Following are the recommended practices for ensuring maximum fifth wheel life.


  1. CLEAN FIFTH WHEEL. Manufacturers recommend regular steam cleaning of the top plate, jaws and legs. Many owner-operators and fleets prefer simply to scrape off the accumulated globs of dirt and grease with a putty knife, brush and cleaning solvent.

  2. INSPECT TOP PLATE. Examine the upper surface and outer edges, looking for damage, missing parts and excessive wear. Use a straight edge to determine the plate’s flatness. Shine a flashlight underneath and look for signs of grease seeping through cracks.
  3. CHECK LOCKING MECHANISM. Inspect the jaw area, looking for damage, missing parts and excessive wear. Use a test pin, available from each manufacturer, to engage the locking mechanism. It should operate smoothly and fit tightly around the test pin. Using homemade test pins is not recommended. Make sure the release handle is secure and straight.
  4. ADJUST LOCKING MECHANISM. Follow the manufacturer’s instructions when adjusting the locking mechanism of your fifth wheel. Regardless of brand, use the proper tool: a test pin, which will be exactly 2 inches in diameter and will fit squarely into the lock area.
  5. INSPECT BRACKET PINS AND LEGS. Look for cracks and other damage. Make sure grease fittings, or zerks, are intact (where applicable) and free of blockage. Pins should show no signs of wear or slack. The top plate should tilt smoothly and freely.
  6. INSPECT TRAILER BOLSTER PLATE AND KINGPIN. Use a carpenter’s square to determine the flatness of the bolster plate and the form of the kingpin. If either shows signs of deformity, replacement is necessary. Use a kingpin gauge to determine wear.
  7. LUBRICATE JAW AND LOCKING MECHANISM. Unlike the top plate, these parts should be coated with a silicone-based spray lubricant or light oil.
  8. LUBRICATE BRACKET PINS. Attach a grease gun to the bracket pin grease zerk. Ask a helper to pry up that side of the fifth wheel with a bar, allowing grease to fill the friction surfaces above the pin. Repeat on the opposite side.
  9. LUBRICATE TOP PLATE. Apply high-quality grease to the rear portion of the top plate. This will be spread across the surface when a trailer is connected.
  10. OPERATE WITH CARE. Use the truck’s air suspension to achieve the top level for backing under a trailer. Ideally, a trailer nose should make contact with the fifth wheel slightly behind the bracket pins, tipping the top plate flat during coupling. When dropping a trailer, crank the landing gear close to the ground, then dump the suspension air to reduce the weight on the fifth wheel before pulling away.

Putty knife
Trouble light
Carpenter’s square
Kingpin gauge
Lock tester
Combination wrenches/pry bar
Shop towels

(800) 874-9780

(888) 396-6501

Jost International:
(800) 253-5105

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