Ok to use 75W-90 Syn in Diff that req SAE 80?

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I have a Yamaha ATV (1999 Kodiak 400). I'm going to change out the front and rear differential fluids this weekend. This is what the owner's manual states:

Quote:
Rear Diff : SAE 80 API "GL-4" Hypoid gear oil
Front Diff : SAE 80 or SAE 80W-90 API "GL-5" Hypoid gear oil.


So I went to walmart and canadian tire. Now canadian tire had 75W-90 full synthetic GL-5 hypoid gear oil. Can I use that in both the front and rear? What would be best? What do you guys recommend?

Thanks
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You probably could, but I think I would use a regular 80W-90 in there. Sometimes Walmart carries Shell Spirax 80W-90 in quarts and that would make a good gear oil for your application.
 
It's ok to use. But, if you'll lose an ounce of hp with the thicker gear oil.

The rear-end must be bigger/stronger and/or has a larger sump then the front-end since it only requires a SAE80/GL4 gear oil. SAE80 is 7cst(like ATF)-11cst(MTF/MTL). I would use Redline MTL, Amsoil MTF, or other equivalent GL4 fluid in the rearend. If you don't mind the ounce of power lose, use the 75w90 GL5.

The front-end requires a GL5. Is it overly stressed? There are not too many SAE80 GL5 gear oil, and 75w85 GL5's are pretty tough to find(Redline/Toyota/...). I would definitely use ANY full synthetic 75w90 GL5 in the front end.
 
Originally Posted By: unDummy
It's ok to use. But, if you'll lose an ounce of hp with the thicker gear oil.

The rear-end must be bigger/stronger and/or has a larger sump then the front-end since it only requires a SAE80/GL4 gear oil. SAE80 is 7cst(like ATF)-11cst(MTF/MTL). I would use Redline MTL, Amsoil MTF, or other equivalent GL4 fluid in the rearend. If you don't mind the ounce of power lose, use the 75w90 GL5.

The front-end requires a GL5. Is it overly stressed? There are not too many SAE80 GL5 gear oil, and 75w85 GL5's are pretty tough to find(Redline/Toyota/...). I would definitely use ANY full synthetic 75w90 GL5 in the front end.

So 80W-90 dino in the rear, 75W-90 syn in the front? Is 75W-90 syn good for LSD? The front diff is a limited slip differential.
 
I would use 75w90 in both and most synth's have the LSD additive if needed for your application.
 
In the end I went with Yamalube Drive Shaft Gear Lube (SAE 80W-90).

Both diff fluids have never been changed since I bought the Kodiak back in 1999.
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Let me tell you, it was quite dark.
 
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