Which oil for diffs?
Thread Starter
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Fleet Mechanic
Joined: Jun 2009
Posts: 1,346
Likes: 4
From: Connecticut
Which oil for diffs?
Im putting a new finned aluminum rear diff cover on soon.My rear diff is a limited slip. Would royal purple 75/140 with friction modifier be right? Can I use the same for the front diff? The truck has 83000 miles, the rear diff fluid is probably close to needing change but should I do the front to or wait more miles?Only use 4/4 in winter maybe 20 times a season...If that matters or is it the age of the oil?How much does the front diff hold?I read the rear is about 3.5 quarts?
Cargo Master
Joined: Oct 2008
Posts: 3,330
Likes: 13
From: Eaton, CO
I used that Valvoline 75W140 w/ the LS additive that comes in it. IMO, I should've used the Motorcraft stuff that doesn't come with the additive already in it. I'm half tempted to get that Valvoline crap out of there and start over.
LS additive won't do anything in the front differential unless you have a LS in there.
LS additive won't do anything in the front differential unless you have a LS in there.
Posting Guru
Joined: Oct 2008
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From: Az
Is the Motorcraft additive better than Valvoline?
Cargo Master
Joined: Oct 2008
Posts: 3,330
Likes: 13
From: Eaton, CO
IDK. I think I jumped the gun and bought that Valvoline fluid and should've just stuck with Motorcraft diff fluid and friction modifier as recommended. So far I've had a bear of a time getting the rear end to stop locking up around slow, tight corners. It tends to act up after the fluid warms up.
Posting Guru
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From: Az
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Post Fiend
Joined: Feb 2008
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From: Lancaster, Pa.
Rob, I changed my rear out with the 75-140 Royal Purple, its got the anti-slip additive already in it but I still had to add a bit more of the Motorcraft friction moddifier to stop the scuffing around corners thing, been great the last 30,000 miles. I think we can use the same 75-140 now per Ford recommendations for the front diff. somebody will correct me if I'm wrong. Jason, if I had those symtums I'd be swapping out that fluid for the Motorcraft or adding more F.M. to your Vavoline, no sense in ruining your rearend, my .2 cents anyway.
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Posting Guru
Joined: Oct 2008
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From: Az
The additive won't hurt anything up front?
Lead Driver
Joined: Jun 2003
Posts: 8,298
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From: Damon (South East Texas)
There isn't anything in there that the friction modifier will hurt or cause slippage. Just an added expense, of the oil, that isn't neccessary.
Thread Starter
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Fleet Mechanic
Joined: Jun 2009
Posts: 1,346
Likes: 4
From: Connecticut
Rob, I changed my rear out with the 75-140 Royal Purple, its got the anti-slip additive already in it but I still had to add a bit more of the Motorcraft friction moddifier to stop the scuffing around corners thing, been great the last 30,000 miles. I think we can use the same 75-140 now per Ford recommendations for the front diff. somebody will correct me if I'm wrong. Jason, if I had those symtums I'd be swapping out that fluid for the Motorcraft or adding more F.M. to your Vavoline, no sense in ruining your rearend, my .2 cents anyway.
Fleet Mechanic
Joined: Nov 2008
Posts: 1,573
Likes: 4
From: Seattle
Too much fm and your diff won't lock when you need it to. It will be too slippery for the clutches to engage, like on a wet or icy incline.