Castrol Limited Slip 80w-90 Oil

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Jan 23, 2003
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ON, Canada
I am working a Ford 9" differential with freshly rebuilt Trac-Lok clutch style limited slip. I am going to fill it with Castrol 80w-90 Limited Slip oil. Does this oil have the friction modifier already added? The guy at the parts store said it does, but not sure how knowledgeable he is.

Previously I always used straight gear oil and added the friction modifier separately. However this was the only 80W90 in stock.
 
It says can be used in LSDs on the bottle but doesn't say if it has the modifier. Regular gear oil can be used in LSDs and open diffs too.
 
If it says it can be used in LSD then it has modifiers in it, if you want a sure thing then get something like redline or bottle that specifically says has friction modifiers.
 
Unless they changed their bottle Castrol is front and center with the words Limited Slip as on this one available from Amazon.


Castrol 80w90 limtited slip.PNG
 
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And if it says GL-5 on the bottle you are fine, this is why for my diffs I bite the bullet most times and purchase the most quality oil....so I'm not second guessing myself, especially having a Jeep.
 
Just went through my gear oil re-education before doing my Ranger diffs.
Limited Slip in the rear only. Total capacity is 8.3 U.S. pints.
The FM is ignored by the open front diff.
I was open to nonFM 80W-90 conventional (adding my own FM to the rear) but "everyone" sided with synthetic gear oils.
Also, the difference between 75W-90 and 80W-90 never came up.
Gotta find a different way to stick it to the man.
 
Limited slip has the modifier. I used Valvoline in my Silverado and I had Kendall in a 12 bolt with Positraction I still have. Brad Penn makes it and I saw something else at O'Reilly the other day. No need to add anything else.
 
Originally Posted by Randy_R
Limited slip has the modifier. I used Valvoline in my Silverado and I had Kendall in a 12 bolt with Positraction I still have. Brad Penn makes it and I saw something else at O'Reilly the other day. No need to add anything else.


Thank you. I don't know why it just doesn't say that clearly on the bottle. I know it says for limited slip, but no where does it state it has additive. FWIW, I also confirmed this through Castrol. The emailed me back today and confirmed the oil contains the additive for the Limited Slip.. I will try it out and see how the LSD works. I can always add an oz or two if it chatters.
 
It's what I've always used in the Tundra in my sig that calls for 80w90 LSD mineral and it works perfectly in my application, LSD still working great at almost 200k, change it every 50k or so, no chatter and never had to add any additives
 
FWIW, this Castrol Gear Oil does not have enough limited slip additive for a 9" Ford differential with a factory style traction-lok limited slip. Using the fluid alone resulted in some noise when turning. I added some Motorcraft additive and it is as quiet as ever.

I hope this information helps someone.
 
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