Rear Differential Question
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Joined: Mar 2018
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Rear Differential Question
The other day I noticed a vibration while driving on the highway. I crawled under my 03 F250 to see which U Joint was bad and smelled differential fluid. I decided to replace the rear differential fluid while under there. I just bought this truck from my uncle and he had the rear end replaced just before I bought it in March. He told me that I had to add an additive to it. What is the name of this additive and what is it for?
Fleet Mechanic
Joined: Jul 2010
Posts: 1,753
Likes: 34
From: Los Angeles, Ca.
If it has a limited slip differential then you need the additive. It's often called limited slip additive, friction modifier, or possibly other things. There are several brands that all do the same thing and any parts store will have it. If the bottle says it's for limited slip differentials it's what you want. Without it the clutches will likely have binding issues and the rear end will be unhappy when you go around turns under power.
Many gear lubes say they don't need the additive, but with a Ford limited slip they often need the additive anyway. Royal Purple in my Explorer had chatter even tho it's stated to not need the additive.
If it doesn't have a limited slip differential then you don't need it.
Many gear lubes say they don't need the additive, but with a Ford limited slip they often need the additive anyway. Royal Purple in my Explorer had chatter even tho it's stated to not need the additive.
If it doesn't have a limited slip differential then you don't need it.
Cargo Master
Joined: Nov 2005
Posts: 2,766
Likes: 56
From: East Tawas, MI
I'm running Mobile 1 as well.
Bottle reads premium lubrication for limited slip differential assemblies. IT However does not say that it contains a friction modifier. My truck danced around corners like a horny square dancer. I thought to myself that this was a new diff and Mobile 1 was supposed to have the modifier integrated. Reread carefully, made calls. WRONG. It just says formulated for LSD's and not that it contains them.
Added Ford modifier and my square dancer left me
JS
Denny
Bottle reads premium lubrication for limited slip differential assemblies. IT However does not say that it contains a friction modifier. My truck danced around corners like a horny square dancer. I thought to myself that this was a new diff and Mobile 1 was supposed to have the modifier integrated. Reread carefully, made calls. WRONG. It just says formulated for LSD's and not that it contains them.
Added Ford modifier and my square dancer left me
JS
Denny
Lead Driver
Joined: Dec 2006
Posts: 7,092
Likes: 145
From: San Diego, CA
I'm running Mobile 1 as well.
Bottle reads premium lubrication for limited slip differential assemblies. IT However does not say that it contains a friction modifier. My truck danced around corners like a horny square dancer. I thought to myself that this was a new diff and Mobile 1 was supposed to have the modifier integrated. Reread carefully, made calls. WRONG. It just says formulated for LSD's and not that it contains them.
Added Ford modifier and my square dancer left me
JS
Denny
Bottle reads premium lubrication for limited slip differential assemblies. IT However does not say that it contains a friction modifier. My truck danced around corners like a horny square dancer. I thought to myself that this was a new diff and Mobile 1 was supposed to have the modifier integrated. Reread carefully, made calls. WRONG. It just says formulated for LSD's and not that it contains them.
Added Ford modifier and my square dancer left me
JS
Denny
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Laughing Gas
Joined: Mar 2004
Posts: 789
Likes: 16
From: West Coast/L.A. Area
I would think the opposite. It would slip just like a "normal" differential vs "limited slip".
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Cargo Master
Joined: Nov 2005
Posts: 2,766
Likes: 56
From: East Tawas, MI
It actually struggled to engage until wheel speed was up there. But cornering was like you had the front hubs locked in on ashphalt. It still locks up at about 10mph wheel speed but doesn't crab the corners.
Talked to my guy and he asked how long I ran this way..........2 months, he said I put two years on the clutch pack
Learnin!!
Denny
Talked to my guy and he asked how long I ran this way..........2 months, he said I put two years on the clutch pack
Learnin!!
Denny
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