Limited Slip Differential Fluid Decisions - for better functionality
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Senior User
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From: Northwest OH
Limited Slip Differential Fluid Decisions - for better functionality
I'm getting ready to change the fluid in my Rear diff (3.73 LS) in my 99.5 F250. I have been disappointed at the "limited slip" factor that I have right now and want better lockup with less slipping. From some of the old (and very very old) threads that I have read, Amsoil is one of the better ones to use.
In the past (referenced in those old threads), the Amsoil 2000 series 75w-140 synthetic could be used in the diff without adding a friction modifier. The problem with that is; Amsoil 2000 has been replaced by Amsoil Severe Gear 75w-140 Extreme Pressure Lubricant.
My concern is when using this with my Limited slip diff. In reading the information page, there is little mention of the Limited slip differential. The only thing I could find is on the bottom of the page that says "If limited slip differential chatter occurs, add AMSOIL Slip-Lock™ friction modifier additive."
Has anyone used this newer oil? Is it the best functioning one out there?
In the past (referenced in those old threads), the Amsoil 2000 series 75w-140 synthetic could be used in the diff without adding a friction modifier. The problem with that is; Amsoil 2000 has been replaced by Amsoil Severe Gear 75w-140 Extreme Pressure Lubricant.
My concern is when using this with my Limited slip diff. In reading the information page, there is little mention of the Limited slip differential. The only thing I could find is on the bottom of the page that says "If limited slip differential chatter occurs, add AMSOIL Slip-Lock™ friction modifier additive."
Has anyone used this newer oil? Is it the best functioning one out there?
Lead Driver
Joined: Sep 2003
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From: Albuquerque
The Motorcraft version is really GOOD stuff. The issue here is the LS locking up when you really need it. So...what many FTE folks do is add in 2oz increments (8oz is recommended by FORD) the friction modifier...until the chatter stops...usually 4oz works best.
Another great gear oil is Royal Purple. No modifier needed...
biz
Another great gear oil is Royal Purple. No modifier needed...
biz
Cargo Master
Joined: Apr 2003
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From: Too close to Houston
When I changed my differential fluid I used the Lubrimatic (sp) brand synthetic fluid and Lubrimatic limited slip additive from O'Rielly's. It runs quiet and works well. Last weekend I rotated my rear tires and was able to break the lugs loose with both tires off the ground and the parking brake wasn't set. I'm guessing I have something like 100 ft-lbs preload.
Cargo Master
Joined: Apr 2003
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From: Too close to Houston
I fill until it is flush with the bottom of the hole and any more would run out. The level has to be high enough to get into the axle tubes since it lubricates the wheel bearings too.
Lead Driver
Joined: Sep 2003
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From: Albuquerque
Originally Posted by Dsl Lover
I believe that I read 3.5 quarts, is that right? Do I add until I can touch it with my pinkie, or add until it comes out the fill hole?
F250/F350 10.50" rear axle
3.3L or 6.9 pints (or 2.90 quarts)
But you have it correct...fill until a small amount dribbles out. I think FORD gives the amount so that we can purchase enough gear oil.
Good luck...
biz
Fleet Mechanic
Joined: Jul 2005
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From: Southern Colorado
Start with no additive and if it binds/chatters, then add some, in 2 oz. increments. You may find that the diff is pleasantly tighter without any additive at all.
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Senior User
Joined: May 2003
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From: Goodrich IL
Originally Posted by SteveH-CO
Start with no additive and if it binds/chatters, then add some, in 2 oz. increments. You may find that the diff is pleasantly tighter without any additive at all.
makes them slip.
Change the oil and leave out the addittive, you may get a little chatter
and if ya dont like that add the additive until it stops.
I had a L/S in one of my other SD's that I orderd, it was limited all right
as in not working at all, but it would chatter!...go figure.
A TrueTrac works very well if all else fails.
The 07 that I have now I bought off the lot, the L/S seems to be workin ok,
anit really put it to the test yet.
Gene
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From: Long Island USA
Same as the other guys. If it's a Sterling 10.5" (single-rear-wheel) like mine, about 4oz of additive seems to work best for me.
Ford says to leave the stock fluid in there unless it's immersed in water. They MIGHT say to change at 100K. Me? I change it every 20K or so just to see if there's anything wrong inside. I'm not the "leave it alone if it ain't broke" sorta guy
I used Mobil 1. Use whatever your wallet can handle. There are very few fluid-related failures with the Sterling since Ford went full-synthetic on them.
Ford says to leave the stock fluid in there unless it's immersed in water. They MIGHT say to change at 100K. Me? I change it every 20K or so just to see if there's anything wrong inside. I'm not the "leave it alone if it ain't broke" sorta guy
I used Mobil 1. Use whatever your wallet can handle. There are very few fluid-related failures with the Sterling since Ford went full-synthetic on them.
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Senior User
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From: Northwest OH
I ended up using Mobil 1. I didn't need to use any modifier - no chatter or any other ill effects. Does that mean my LS clutches are gone? At only 51K? Or does Mobil 1 just not need it? There weren't any notations either way on the bottle. It took 3 bottles (3 quarts) exactly.
Elder User
Joined: Jul 2006
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From: right here in michigan
i used mobil 1.did this because diff was useless as delivered .it's "a little" better,will at least spin both on a powerbrake.we'll see how good it is in the snow.if it still sucks something else will be going in there.
Lead Driver
Joined: Sep 2003
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From: Albuquerque
Originally Posted by Dsl Lover
I ended up using Mobil 1. I didn't need to use any modifier - no chatter or any other ill effects. Does that mean my LS clutches are gone? At only 51K? Or does Mobil 1 just not need it? There weren't any notations either way on the bottle. It took 3 bottles (3 quarts) exactly.
biz
Elder User
Joined: Jul 2006
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From: right here in michigan
it does say it's for use in limited slip diffs.i didn't add any modifier to mine either and theres no chatter.i'd rather it didn't have any modifier in the lube already and i could've added a little modifier at a time till it quit chattering.
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Senior User
Joined: Mar 2006
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From: Northwest OH
Since my Mobil 1 fluid change, I am officially disappointed. Now, in the wet, I get a complete 1 wheel peel - like my LSD isn't even there. I didn't use friction modifier, either. What gives? My truck only has 52k on the odo. What can I do? What should my next step be?