Ask The Mechanic

Hydraulic Lift Lock

(Progressive Farmer image by Steve Thompson)

READER: I have a problem with a Ford 8N tractor that I bought to restore. I finally got it running, and the hydraulic lift will raise, but it won't go down. It just locks up at the top. It will drop down a little in time if the tractor is not started. I removed the top cover, and everything seems to be OK. However, it appears that the control rod is bent. Is it supposed to be straight? Can you tell me why the lift will not go down? The control valve is very hard to move down unless the tractor has not run in a while.

STEVE: Yes, the control rod is supposed to be straight. It sounds like your problem is that both valves in your hydraulic pump are stuck. When this happens, the pump will raise the lift arms then send the hydraulic fluid over relief. I bet the engine runs partially loaded because of the pumping of the hydraulic over relief. No oil can leave because the valves are stuck. You will need to drop the pump assembly out of the tractor from the bottom, but before it will come out, you must remove the PTO shaft. You will lose almost all of the oil in the tractor (5 gallons). Usually, water will be the cause of the valves sticking. The reason the control arm is bent is that someone "strong-armed" the control lever when trying to move it down against blocked hydraulic pressure. It moves easily after the blocked hydraulic pressure leaks off. The hydraulic pump assembly has a drain plug, but many tractors have never had this oil changed -- ever.

> Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email mechanic@progressivefarmer.com.

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