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Jeep Wrangler YJ
YJ General Discussion
Improving synchro shifting problems by using different gear lube weights or additives?
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<blockquote data-quote="Gary747" data-source="post: 429466" data-attributes="member: 19207"><p>Just to follow up... I use Mopar ATF in my transmission (AX-15) ONLY because it is the Jeep manufacturers brand... I've no specific technical reason other than brand loyalty. As for 30W engine oil in the Transfer Gearbox, I actually called the rebuilder (The Gear Shop, Middle River, MD) and asked why they void the warranty if I use the red ATF fluid. They said that the transfer gearbox is vented and that ATF "mists" pretty heavily when energetically lifted by gear action (lower shear stability), resulting in a gradual loss of fluid via the vent. All things being equal, many owners don't check the transfer oil level very often and end up running the transfer gearbox at too low of an oil level for extended periods. 30W engine oil "mists" much less and adheres to the rotating parts inside the gearbox much better, greatly reducing the possibility of running with low lube levels and improving internal lubrication. I used to be in the group that didn't regularly check the transfer gearbox oil levels very often, but when I did, I found the ATF level to be pretty darn low. However, I use ATF in the transmission (with spinning gear shafts) and I don't seem to be losing ATF fluid over time. Whatever, it works for me.</p><p></p><p>The cold oil "shifts good" and the warm oil "shifts hard" observation may be associated with the oil chemistry. Multi-weight fluids such as 75W90 or 5W30 change viscosity inversely with temperature. The lower the temperature the "thinner" oil, and as the oil heats up, it get "thicker". Starting an ice cold engine requires thinner oil in order to move around the engine, but the oil needs to "thicken up" as everything gets hot. So, while GL4 as suggested by Gilaguy23 is definitely the way to go for normal transmission lubrication, you might also consider a single weight version if you can find it. After my experiences, I'm more comfortable with lighter weight lube oils when dealing with "meshing" rotating components, but I stick with 75W90 in the axles.</p></blockquote><p></p>
[QUOTE="Gary747, post: 429466, member: 19207"] Just to follow up... I use Mopar ATF in my transmission (AX-15) ONLY because it is the Jeep manufacturers brand... I've no specific technical reason other than brand loyalty. As for 30W engine oil in the Transfer Gearbox, I actually called the rebuilder (The Gear Shop, Middle River, MD) and asked why they void the warranty if I use the red ATF fluid. They said that the transfer gearbox is vented and that ATF "mists" pretty heavily when energetically lifted by gear action (lower shear stability), resulting in a gradual loss of fluid via the vent. All things being equal, many owners don't check the transfer oil level very often and end up running the transfer gearbox at too low of an oil level for extended periods. 30W engine oil "mists" much less and adheres to the rotating parts inside the gearbox much better, greatly reducing the possibility of running with low lube levels and improving internal lubrication. I used to be in the group that didn't regularly check the transfer gearbox oil levels very often, but when I did, I found the ATF level to be pretty darn low. However, I use ATF in the transmission (with spinning gear shafts) and I don't seem to be losing ATF fluid over time. Whatever, it works for me. The cold oil "shifts good" and the warm oil "shifts hard" observation may be associated with the oil chemistry. Multi-weight fluids such as 75W90 or 5W30 change viscosity inversely with temperature. The lower the temperature the "thinner" oil, and as the oil heats up, it get "thicker". Starting an ice cold engine requires thinner oil in order to move around the engine, but the oil needs to "thicken up" as everything gets hot. So, while GL4 as suggested by Gilaguy23 is definitely the way to go for normal transmission lubrication, you might also consider a single weight version if you can find it. After my experiences, I'm more comfortable with lighter weight lube oils when dealing with "meshing" rotating components, but I stick with 75W90 in the axles. [/QUOTE]
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Jeep Wrangler YJ
YJ General Discussion
Improving synchro shifting problems by using different gear lube weights or additives?
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