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Fifth Wheel Coupling buying guide — what to know before you buy

A fifth wheel coupling is the primary connection between a heavy goods vehicle (HGV) tractor unit and a semi-trailer. It consists of a horseshoe-shaped plate mounted on the tractor that receives the trailer's kingpin, locking it securely for towing. Proper maintenance and timely replacement of worn fifth wheel components are critical for road safety and compliance with commercial vehicle regulations.

Inspection and wear limits

Fifth wheel couplings must be inspected regularly as part of the vehicle's maintenance schedule. Worn components increase play between tractor and trailer, affecting handling and potentially allowing the trailer to separate.

Check jaw locking mechanism for positive engagement and no excessive free play
Inspect the coupling plate surface for cracks, scoring, or deformation
Measure kingpin wear — replace if play exceeds manufacturer's tolerance
Check lubrication — a dry fifth wheel causes rapid wear and handling problems
Inspect mounting brackets and bolts for cracks or corrosion

Lubrication and maintenance

Regular greasing is the single most important maintenance task for a fifth wheel coupling. Insufficient lubrication leads to rapid wear, trailer wander, and coupling failures.

Apply fifth wheel grease to the entire upper plate surface before every coupling
Use a grease approved for fifth wheel use — standard chassis grease is not sufficient on some applications
Automatic lubrication systems are available and recommended for high-mileage operations
Clean the plate and re-grease after operating in dusty or muddy conditions
Record lubrication intervals in the vehicle's maintenance log for compliance purposes

Frequently Asked Questions

How often should a fifth wheel coupling be inspected?

A visual check should be carried out before every journey as part of the driver's daily walkaround. A detailed mechanical inspection should be performed at each scheduled service interval or as required by national regulations.

What is kingpin wear and why does it matter?

The kingpin is the pin on the trailer that locks into the fifth wheel jaw. Excessive wear on the kingpin or the jaw increases articulation play, which can cause trailer wander, snap steering, and, in extreme cases, trailer separation.

When should a fifth wheel plate be replaced?

Replace if the plate shows cracks, deep scoring across the kingpin channel, deformation, or if jaw locking force falls outside the manufacturer's specification. Worn components should never be welded and returned to service.