Stiction—short for static friction—occurs when a hydraulic cylinder moves in a jerky, stop-start pattern instead of smoothly. Also called stick-slip, this problem is especially common at low speeds. For dump truck cylinders, garbage truck cylinders, construction machinery cylinders, and agricultural machinery cylinders, stiction can ruin positioning accuracy and accelerate seal wear. Even large custom cylinders built with premium components can develop stiction if underlying causes are not addressed.
What causes cylinder stiction?
The most common cause is air trapped in the hydraulic system. Air compresses, then releases suddenly, creating a jumping motion. Air typically enters through the pump intake, low reservoir oil level, or loose fittings. The second most common cause is excessive seal friction. This happens when seals are incorrectly specified, worn out, or running dry due to inadequate lubrication. Third, tight fit between the rod and guide bushing creates mechanical interference. Fourth, contaminated oil changes friction properties. Fifth, rod bending or misalignment introduces uneven drag.
Step-by-step troubleshooting
Start with the simplest check: bleed air from the cylinder. Run the cylinder through several full strokes at low pressure while cracking the bleed port (if equipped) or loosening the hose fitting slightly at the end of stroke. If stiction disappears, air was the problem. Next, inspect the rod surface. Look for rust, scoring, or uneven oil film. A dry or patchy oil film suggests lubrication problems or worn rod seals. Then, check alignment. Disconnect the cylinder from the load and run it unloaded. If stiction disappears unloaded but returns under load, the issue is likely misalignment or a bent rod. Finally, evaluate oil condition. Milky oil indicates water contamination. Dark, smelly oil indicates oxidation. Either can cause stiction.
Preventive measures
Use cylinders with proper bleed ports, especially on large custom cylinders with long horizontal runs. Specify low-friction seal materials such as PTFE-loaded polyurethane for applications requiring very slow, smooth movement. Maintain clean, dry hydraulic oil with the correct viscosity. Replace wiper seals regularly to prevent contaminant ingress. On dump truck cylinders and construction machinery cylinders that cycle frequently, schedule annual seal inspection.
When to rebuild
If stiction persists after bleeding, alignment check, and oil change, the cylinder likely needs disassembly. Inspect the rod for straightness and surface damage. Inspect seals for uneven wear or hardening. Inspect the bearing for scoring. Rebuild with a full set of premium seals, wipers, and wear rings. We use only high-quality seal kits from reputable global suppliers on every cylinder we service or manufacture. For garbage truck cylinders and agricultural machinery cylinders where smooth operation matters for safety and productivity, do not tolerate stiction—fix it early.