Best type of gear oil for Jetstar 3

[Jetstarring]

Greetings!

First time poster here! I want to thank you all for your posts that have helped me revive the '68 Jetstar 3 I inherited from my late grandfather. I am hoping you can help me with my next task:

I am clear from the Owners Manual and IT manual on how to change the transmission/differential fluid, but need your help choosing the right oil. The owners manual I got from Jensales recommends SAE 80W oil, but most folks online say "their book recommends 90W". In addition, 80W is not readily available anymore so either 80W-90 or straight 90W will have to do, but I am not sure whether to pick GL-1, GL-4, or GL-5 ratings. GL-5 80W-90 is readily available in NW PA, I don't know if the Jetstar 3 uses yellow metals that would require GL-1. My research turns up answers for Ford and Case tractors but hardly a word for MM's.

Can anyone here share with me what weight and rating oil they've successfully used in their MM transmission/rear end? Would I be OK with filling up with 80W-90 GL-5?

 

[Jetstarring]

(quoted from post at 22:03:48 10/14/18) Greetings!

First time poster here! I want to thank you all for your posts that have helped me revive the '68 Jetstar 3 I inherited from my late grandfather. I am hoping you can help me with my next task:

I am clear from the Owners Manual and IT manual on how to change the transmission/differential fluid, but need your help choosing the right oil. The owners manual I got from Jensales recommends SAE 80W oil, but most folks online say "their book recommends 90W". In addition, 80W is not readily available anymore so either 80W-90 or straight 90W will have to do, but I am not sure whether to pick GL-1, GL-4, or GL-5 ratings. GL-5 80W-90 is readily available in NW PA, I don't know if the Jetstar 3 uses yellow metals that would require GL-1. My research turns up answers for Ford and Case tractors but hardly a word for MM's.

Can anyone here share with me what weight and rating oil they've successfully used in their MM transmission/rear end? Would I be OK with filling up with 80W-90 GL-5?

 

[Jetstarring]

Sorry, not sure why that posted as a quote. I can't delete it either so please ignore that second post.

No one change their transmission oil recently? I really could use some input on whether to use GL-1 or GL-5 gear oil in this Jetstar 3. I think it's transmission is similar to other late 60s Molines so if you've changed transmission oil in those recently I'm eager to hear what you've used!

 

[DWF]

I have a JetStar 3 that I recently purchased. I too am thinking of changing that oil. I looked in my manual and it said to use grade 80 gear oil meeting military spec 2105B. I checked on line and that is the equivalent of GL4. I know that with yellow metal you are to use GL1. I don't know how readily available GL4 is, but I'm sure it would be in 80-90 or straight 90 like GL1 is.
Good luck, let us know what you find.

DWF

 

[Jetstarring]

Thanks for the info and reply! I looked up what you mention and agree that GL-4 is what I should aim for, but unfortunately its is unobtanium in 5 Gallon buckets. My Jetstar 3 has Ampli-Torque so I need 9 gallons of oil (!!).

I think what I'm going to do is get the Napa GL-1 90W and see how it likes it. I think that should be OK compared to whatever is in there now.

 

[DWF]

I think I'm going to need to change mine too. GL-4 is available but not very common. I don't see it for sale in 5 gallon pails either.

DWF