Decades of rust left abrasive particles in the tractor’s three-point lift cylinder, causing loss of lift power due to failure of seal rings on the piston. Photos by Scott Nesbitt
Your ears may be the tool needed to diagnose a tractor’s weak three-point lift.
The problem may be worn rubber in the hydraulic piston mounted under the driver’s seat. Repairing the issue can take time and require some fairly major surgery, but the cost is usually low. No special tools or skills are needed for repair other
than the talent to keep things clean and lubed.
On many tractors, you should hear a squealing sound from the pressure-relief valve after the lift arms reach their maximum height. Moving the lift-control lever sends pressurized fluid into the cylinder. When the piston hits the end of the cylinder, there’s
no room for more fluid. Something’s got to break, or something’s got to give — namely, the pressure-relief valve opens.
The lift cylinder and piston are the heart of the three-point tractor hitch design that has been used (with manufacturer variations) since the 1920s. Shown is the system used on old Yanmar compact tractors.
The squeal comes from oil being pumped at high pressure — in the ballpark of 2,500 pounds per square inch — through a small hole that directs excess fluid into the reservoir. Lack of noise could mean the lift piston’s seal ring is leaking,
letting fluid flow past the piston rather than pushing it. Listening for a squealing relief valve is a lot quicker than testing for low hydraulic pressure (bad pump) or blaming a failing relief valve. Another clue is that the lift works when the hydraulic
oil is cold, but not when warm, because cold oil has higher viscosity.
The replacement rings shown with the piston cost less than $15. The lift design is pretty much universal and about 100 years old. Different companies use various terms — seal, packing, O-ring, wiper, seal kit, etc. — to name the black O-ring
and white stiffener ring seen with the piston photo. A dealership parts-counter person will know what you need.
It wasn’t easy finding parts online for my 1977 Yanmar tractor, but the repair work was simple. Close inspection found scratches and scars on the stiff old O-ring.
Flaws in the piston’s sealing ring let pressurized fluid escape past the piston. Note the rust particles scraped off the cylinder wall by the white stiffening ring.
The cylinder bore and piston were cleaned with brake-parts cleaner, 0000 steel wool and 800-grit sandpaper and triple-rinsed to eliminate grit. The big O-ring was warmed in 120-degree oil and eased into place, making sure it was not rolled in. Assembly
just took time, not a lot of skill.
After the lift arms were working again, gauges showed the hydraulic pump was about 80 psi below the 2,250 spec, but we’ll live with that and keep the $400 a new pump would cost.
Scott R. Nesbitt is a freelance writer and former GCSAA staff member. He lives in Cleveland, Ga.