Path of hydraulic fluid to engine crank case.

Raised on a Deere · Sep 29, 2020

Up until now I have been proceeding on the assumption that the only path for hydraulic fluid into the engine crank case would be through the pump seals. But I would like to rull out that there is no other possible way. The wet clutch is held engaged under hydraulic pressure. As soon as hydraulic pressure bleeds off, clutch is disengaged. Because of not being familiar with that part of these tractors I just have started to wonder if there could be some possible path to the rear main crankshaft seal. Because of that I posted the following in the Yanmar forum on this site to get any specific yanmar experience. but I thought I would post here because ther is a much wider audience generally familiar with hydraulic systems on tractors.

The post in Yanmar forum is as follows: --- I got the pumps off and the seals appear to be pristine. Exactly like the new ones. So no obvious failure of the seals. I now suspect something internal in the pump that is allowing over pressurization of the seal so I am getting ready to take the pump apart and examine as closely as I know how. But there is an incredible thought in the back of my mind. Could hydraulic fluid enter by means of the crankshaft seal at rear of engine where it joins up with the clutch. This Yanmar has a wet clutch and is operated hydraulically. I know transmission case is not under pressure but I haver never seen these or similar tractors taken apart at the bellhousing. Is hydraulic oil separated from the crank case by a seal. I am looking up some diagrams to study this out. I hope someone who knows can tell me that no way for hydraulic fluid to enter engine by way of the rear crankshaft seal.

Raised on a Deere · Sep 29, 2020

I have disassembled the hydraulic pump and replaced the inner seal, the funny zig saggy thing that seals to the outer plate. The old seal was very pliable and no signs of deterioration or cracks as I carefully looked under a good light as I flexed the entire way around. I replaced the shaft seal as well and am proceeding to reinstall and try out. I do not have the feeling I have fixed anything. But I wont complain if it is fixed.

ptsg · Sep 29, 2020

Check the vent for the transmission. If it's plugged, it can create back pressure on the pump which would push through the pump shaft seal.

Raised on a Deere · Sep 30, 2020

OK a bit of an update. The vent was clear. I decided to go ahead and tear down the power steering pump also. I initially did the hydraulics pump because I was aware of an incident where my son blew a hose when he caught the bucket in the tilted down position on an obstruction as he was moving pretty fast. Hose popped like a balloon. After this incident the bucket would drift down eventually dumping its load after a few minutes if you did not keep working to keep it level. System has worked well after that incident(except for droop) for 3 years. So when the fluid showed up in crank case recently I suspected that pump and it is the one I reported in earlier posts as finding in pristine condition when I tore it down. I replaced the seals anyway and was thinking i would reinstall both pumps and see if I had made any improvement, but I was nagged at the thought of not being able to tell which pump was leaking if the leak was still there so I decided to tear down the power steering pump even though I did not have any of the interior replacement seals, only a shaft seal.

Glad I did, all seals looked good but I found wear in the drive gear bearings sleeves such that the gear teeth had scored the pump bore for that gear. Scoring was not bad but definitely gear was digging away at its bore. I replaced the shaft seal and will drive for a few days to confirm either no leak now so I can continue working and order pump to have on hand for the inevitable or if it leaks stop work and order a power steering pump.

It will be awhile before I know much more. I just wanted to report that I actually found this wear so the problem is not entirely left with no possible explanation. That wear could be the source of the leak because the shaft has worn its bearing allowing off center to the shaft seal. BTW disassembly and reassembling was very simple, a very easy repair. I just stress a bit over the idea of throwing $500 parts at a problem. But if pump wear is indicated then heck yea, just go buy a new pump and get on with tractor-ing.