Go BottomShibaura 5040T Oil mixing in Transmission
 | greenmile
Join Date: Dec 2024 Posts: 1 
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2024-12-17 201849
Have engine oil transferring into transmission. I am finding it hard to believe it would be going from rear engine seal as it would have to fill the bell housing then track past the front transmission seal. Also should show a leak around bell housing if that was happening.
Any ideas?
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| Tractorpoint
Join Date: Oct 2006 Posts: 20 NJ
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2025-08-01 201907
You're absolutely right to question whether the engine oil is getting into the transmission through the rear main seal and bellhousing—it’s possible, but not the most likely path, especially if there's no oil dripping from the weep hole in the bellhousing.
Here are some more likely explanations for engine oil getting into the transmission on a Shibaura 5040T (or similar Ford/NH tractors based on the Shibaura platform):
🔧 1. Hydraulic Pump Driven Off Engine
Some of these tractors have engine-mounted hydraulic pumps (often gear-driven off the timing gears or camshaft) that send fluid to the transmission/rear end for hydraulic functions. If the shaft seal or pump housing fails, engine oil can be pushed into the hydraulic circuit—and from there into the transmission sump.
Check:
Where is your hydraulic pump located?
Is it engine-driven and connected to the hydraulic reservoir shared with the transmission?
If the pump is mounted directly on the engine and sends hydraulic fluid to a rear-reservoir transmission, that’s your most likely transfer point.
🔧 2. Common Breather or Crankcase Vent Routing
In some models, the crankcase vent or breather system can be poorly routed or malfunctioning, allowing oil mist or actual liquid oil to flow backward into shared components like the transmission breather or fill tube.
Unlikely unless someone modified something, but worth checking.
🔧 3. Transfer Through PTO or Dual Shaft Systems
If the tractor has a live PTO or dual input shaft configuration with one shaft running inside the other (like engine-to-transmission and PTO together), there's sometimes a path through bad seals between compartments. If the seal between the crank-driven PTO and transmission fails, and the engine runs at pressure (while the trans runs at slight vacuum or neutral), engine oil can be drawn in.
Check:
Diagram of PTO and input shaft seals
For any design where compartments are only separated by a lip or o-ring seal
🔧 4. Someone Topped Up Transmission with Engine Oil
This sounds too simple, but if the oil level is rising slowly and not quickly, someone may be mistakenly adding engine oil to the wrong fill port. Double-check fill and check ports and make sure the engine dipstick and trans level are both accurate.
🔍 HOW TO CONFIRM THE SOURCE:
To test the origin of the oil:
Dye Test: Add UV dye to engine oil and see if it shows up in the transmission after a few hours of operation.
Smell and Feel: Engine oil tends to be thinner, darker, and smell different than trans/hydraulic fluid.
Check Transmission Breather: If oil is bubbling out, you may be overfilling or pressurizing the transmission.
✅ Next Steps:
Inspect engine-mounted hydraulic pump (or any return lines from engine to transmission).
Look up parts diagram for seals between engine and transmission input shafts.
Use dye test or oil sample comparison to confirm type and source of oil.
Check bellhousing weep hole—should be dry if rear main isn’t leaking. ....
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