Rear Diff. Lube
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Senior User
Joined: Aug 2004
Posts: 165
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From: NEBRASKA
Rear Diff. Lube
I have an early '99 PSD 4X4 with limited slip 3.73's. I want to change the lube in the rear differential. There is a tag that says 140 weight Synthetic only though. I have been to every parts store, farm supply, and international shop in town. No one carries it. Can I change to a lighter weight or more readily available lube?
Freshman User
Joined: Oct 2004
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To add to the question above , is there an additive you use because of the limited slip diff. I remember reading something about an additive to help keep the clutches in the limited slip from making noise
Richard.
Richard.
Postmaster
Joined: Nov 2004
Posts: 2,854
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From: New Hampshire
the clutches don't make noise, they will just "grab" when you go around a corner... you can feel the tires "hop"... new synthetic is what i had put in my diffs... that fluid had the friction modifier and now no more "hop"... i had all the driveline fluids changed over to synthetic... VERY expensive... but the truck runs so much smoother..!
FTE Leadership Emeritus
Joined: May 2001
Posts: 13,653
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From: Cabot, Arkansas
It's called friction modifier. What it does is makes the diff. fluid more "slippery". I do not use friction modifier in my limited slip, I prefer the added traction of having both wheels spinning when neccessary.
Ford recommends 8 oz. of modifier in the 10.5" rear, but in my estimation that is too much. If you are going to use it, I'd recommend you start with around 2oz. and add as little as neccessary to get the rear as quiet/smooth as you desire.
Ford recommends 8 oz. of modifier in the 10.5" rear, but in my estimation that is too much. If you are going to use it, I'd recommend you start with around 2oz. and add as little as neccessary to get the rear as quiet/smooth as you desire.
