How Do You Choose Between a Steel-on-Steel and a Maintenance-Free (PTFE-Lined) Spherical Plain Bearing?

What does "maintenance-free" actually mean?

It describes the sliding contact, not the whole joint.

A maintenance-free bearing has a self-lubricating layer, often a PTFE composite or PTFE fabric, between the steel surfaces. Routine regreasing is not part of its intended use. Wear, inspection, sealing and correct installation still matter: the term describes a self-lubricating sliding contact, but it does not take the bearing out of scheduled inspection. A sealed steel-to-steel bearing can still need grease. "No grease fitting" is a construction detail. "No maintenance of any kind" is a promise nobody can keep.

How do the two compare?

The table gives directions for selection. It is not a load or life comparison between brands. Use the exact maker's calculation and current product data.

When does steel-on-steel make sense?

When the loads are alternating or severe, and you can reliably get grease to the contact.

Bearings that need maintenance suit alternating loads, medium to large swivel movements and medium sliding speeds. Choose steel-to-steel when severe static, alternating or shock load favours that sliding pair and the machine can reliably deliver the specified lubricant.

That second half is the catch. The grease path belongs on the drawing: the drilled passage must meet the groove in the ring after installation, a shoulder must not block a hole, grease must have somewhere to go, and the nipple must still be reachable in the finished machine. A grease nipple on the outside of a housing is not proof that the bearing is lubricated. Grease and intervals are covered in Q1-08.

When does a PTFE-lined bearing make sense?

When the pivot is hard to reach and the loads are within what the liner is made for.

The steel-on-PTFE pairing is maintenance-free and is preferably used for one-sided loads and for small to medium impact loads. A liner removes scheduled greasing, provided its pressure, speed and environment limits suit the job. Check the exact maker's limits for your bearing.

Two cautions:

• Do not add grease out of habit. In a steel-to-PTFE bearing a little PTFE transfers to the hard surface during running-in, and that transfer is part of how it works. External lubricant on those sliding surfaces can disturb self-lubrication and shorten life, and many maintenance-free designs must not be lubricated at all (Q1-01).
• Do not generalise. PTFE fabric, PTFE sintered bronze and PTFE fibre composites are different systems. Some documented designs allow initial or occasional lubrication. The bearing designation and its own technical sheet decide.

The liner wears, and clearance grows as it does. Set a measurable end-of-life criterion such as allowable radial play, noise or positioning error, instead of "run until failure" (Q1-14).

Does the kind of movement change the answer?

Yes. A loaded bearing that oscillates or tilts is a dynamic wear case, even if it moves slowly.

• A constant-direction load with tiny movement. Review grease starvation for steel-on-steel and local liner wear for PTFE-lined bearings.
• Alternating or shock load. Steel-on-steel can be a useful starting point if the specified grease reaches the contact.
• A pivot that is hard to reach. A maintenance-free liner removes scheduled greasing, if its limits suit the job.
• Frequent movement at higher sliding speed. Check heat and the allowed pressure-speed range for the exact pairing (Q1-04).

What should you tell the supplier before ordering?

• The normal and the peak load, and their direction, including reversals.
• The swing angle, how often it swings, and the speed.
• The temperature range (Q1-12).
• The dirt, water or chemicals present.
• Whether anyone can reach the bearing for greasing after the machine is built.
• The wear or play at which you want the bearing replaced.

Which type suits a suspension pivot on an off-road or race vehicle?

It depends on the peak load and on whether anyone will reach the pivot. A suspension joint sees short, hard peaks (landings, bump-stop hits), many small movements near ride height, and mud, sand and water. Steel-on-steel suits that load pattern if the joint can be greased and checked, and the grease path is kept clean. A PTFE-lined bearing suits a pivot that is hard to reach, but only if the liner's pressure limit covers the peak and the grit is kept out, because sand embedded in a liner wears the ball.

Two things differ from industrial machinery. The bearing has to survive the peak, not the average load. And the "maintenance schedule" is a workshop visit or a pit stop, so decide beforehand who greases the joint, and after what (a water crossing, a wash, a rough run). If in practice nobody will do it, a sealed liner type is the better choice; if it is every service, steel-on-steel with a nipple you can reach with the wheel on is realistic. SYZ's spherical plain bearing buyer's guide and uniball cups pages cover the bearing and cup-housed formats. The pressure limit of a liner comes from the bearing maker, and whether a bearing is acceptable at a given pivot is the vehicle designer's decision.

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