L3901 Hydraulic Leak

   / L3901 Hydraulic Leak #1  

Bruce Smith

Aug 11, 2007
I have a Kubota L 3901 with a little over 900 hours. I noticed an oil puddle on the shop floor after warming up the tractor. The oil was I believe Transmission/ Hydraulic oil. I shut it down immediately. Temperature was below freezing in the garage. The oil was to clean to be engine Oil. The dip stick on the center of floor board was at the add mark. I raised the hood and the trickle was coming down the middle side of the engine that lines up with the alternator (Left Side) from the driver position. It's so cramped in that area I couldn't assertain even with a brite light where exactly where the source of the leak was. I have it at the dealership to assertain the leak. They are still trying to identify. I recommended they put Dye in the oil to see it better. I cannot figure what Hydraulic item is within that area to be the culprit. Any help would be appreciated. The leak is not under pressure. HELP!!
   / L3901 Hydraulic Leak #2  
Often the hydraulic pump is driven off the gear train at the front of the engine that also drives the cam. It will be a cylindrical structure that attaches to the back of the front engine cover and lays alongside the engine. There will be two or three hoses attached to it. One will run from the inlet filter that's under the tractor.
   / L3901 Hydraulic Leak #3  
John Deere makes an hydraulic die,can buy online for about $15.Last forever.Very good idea to use it,just found a leak in the snow I would never have seen with the clear oil.
   / L3901 Hydraulic Leak #4  
I'm betting the culprit is the suction side of the hydraulic system. Easy to check. The suction side are the hoses and connections from the transmission to the spin-on hydraulic filter, and then up to the inlet port of the hydraulic pump located on the side of the engine.

Leaks in the suction side don't show when the system is running, only when the motor is shut off. You can check that by looking at the hydraulic/transmission dipstick while it is running and seeing if the oil looks like it has lots of tiny bubbles instead of being clear. It will clear up in a couple of hours. And once the hydraulic is not pulling a suction, the oil in the suction line will gradually leak out. Look for an unusually wet end on a hose. Often where a worm drive clamps a hose to a metal tube fitting.

Suction leaks are loose fittings or the suction hoses aging and getting microscopic cracking. The suction side is from the sump to the spin-on hydraulic filter, and then up to the inlet port of the hydraulic pump on the side of the engine.

   / L3901 Hydraulic Leak #5  
I'm not familiar with common rail Kubota engines, but think the hydraulic pump drives off the back of the fuel camshaft and mounts on the right side, so I doubt the pump has any part in the leak.