This is the same warning covered in why you should never grease PTFE-lined joints, described through its formal name in materials engineering: three-body abrasion. If you’ve heard this called the "grinding compound effect" and want the mechanical term for it, this is that.
The Three-Body System
A PTFE-lined rod end normally runs a simple two-body interface: a hardened ball sliding against the PTFE liner. Add grease to a joint that isn’t fully sealed against dirt, and you introduce a third body into that system — trapped abrasive particles. Grease is sticky specifically, which is the problem: instead of letting grit fall away or blow off, it holds contaminants against the ball-liner contact zone. Every oscillation of the joint drags those particles through the interface again.
That’s a textbook three-body abrasion system: ball → abrasive particle → liner, with the particle acting as a tiny cutting medium at every cycle. The particle scores the PTFE surface, generates more debris, that debris mixes into the grease, and the mixture becomes progressively more abrasive over time — which is exactly the "grinding compound" description.
Why Design Intent Makes This Worse for PTFE Joints Specifically
QA1, a rod end manufacturer, explicitly distinguishes the two constructions on this point: metal-on-metal joints can benefit from occasional grease as part of how they’re designed to run, while PTFE-lined joints are built to be self-lubricating and don’t get the same benefit from added lubricant. Greasing a PTFE-lined joint isn’t a neutral extra precaution — it’s applying a maintenance strategy the design wasn’t built around, with the abrasion risk as the actual cost.
For the full mechanism (how the PTFE transfer film normally forms, why lubricant disrupts it, and what correct maintenance for a PTFE-lined joint actually looks like), see The Lubrication Myth: Why You Should Never Grease PTFE-Lined Joints.
Related reading: The Lubrication Myth: Why You Should Never Grease PTFE-Lined Joints · The PTFE (Teflon) Liner: How Self-Lubrication Actually Works
