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Rear Differential Oil LS vs nonLS

prayforsurf0

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It was a few years ago, but I've changed both differentials oil. I believe I remember that I do not have a limited slip differential in the back (can someone remind me how to make sure of that) is it on the tag bolted to the cover ? Or somehow coded in the VIN ?

Anyway, I bought new Mobil 1 75W-140 for the rear as I plan to change the rear bearings and seals. I noticed when the new oil came in the mail that the label said, "limited slip friction modifier included".

I realize that you need to add this modifier if you have a LS diff. But what if the case is that I do NOT have LS differential...is it safe to use gear oil that has a friction modifier included in a non LS differential ?
 


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koda2000

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The axle code on the driver's door jam sticker will tell you which rear diff you have (example D4 = 3:73 limited slip). You can Google Explorer axle codes to find out what they mean.

Many find that unless you add the Ford LSD additive you may get noise or roughness when corning, regardless of what the oil bottle says.

Edit:
41 — 3.27 non-limited slip (Explorer/Mountaineer)
45 — 3.55 non-limited slip (Explorer/Mountaineer)
46 — 3.73 non-limited slip (Explorer/Mountaineer)
42 — 4.10 non-limited slip (Explorer/Mountaineer)
D1 — 3.27 limited slip (Explorer/Mountaineer)
D4 — 3.73 limited slip (Explorer/Mountaineer)
D2 — 4.10 limited slip (Explorer/Mountaineer)
 




prayforsurf0

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Thank you for that guidance. And what if I do not have a LS differential, but add this gear oil I have that includes the friction modifier ? Acceptable ?

I just ran out and looked. Axle code is 45. I saw some conflicting answers regarding this code, but the general consensus seemed to be that I have 3.55 open
 




shucker1

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Friction modifier in a Non-LS rear end will not hurt it.

The modifier is there to change the friction co-efficient of the clutch packs in an Limited Slip Rear end allowing some "Slip" while cornering.
 




koda2000

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If the gear oil you're using says it contains an LSD additive and you don't have a LSD rear diff, that's okay.
 




prayforsurf0

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Thank you everyone for your responses on this matter. Much appreciated.
 




Austin Healey

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I'm replacing the differential fluid in my '97 Explorer (w/ limited slip), and the owner's manual (and diff tag) calls for 75W140 synthetic. The manual also says you're supposed to add 4 ounces of friction modifier. So, if I have to add the modifier anyway, do I really need to use the synthetic (at three times the price, in a 20-year-old vehicle)?

The manual also says diffs using the synthetic are "lubricated for life," and the lube doesn't have to be changed unless it gets wet. But except for the "lifetime" aspect, I don't see any other advantage to the synthetic. The truck only has about 80k miles, and I'm not putting on high miles or towing, so unless I hear convincing arguments otherwise, I plan to use conventional 75W140, with friction modifier added. Comments?
 




shucker1

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so unless I hear convincing arguments otherwise,

In all reality they work better at both high and low temperature extremes and protect moving parts better than conventional.

It is your truck so you can do as you wish.

Just saying that by using conventional you may be looking at replacing or rebuilding the rear end sooner than you think.
 




koda2000

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@Austin Healey - If you plan on keeping the vehicle for a few years or more, I would change it, use the 75W140 synthetic and add the friction modifier. Odds are you'll never have to worry about it again. If you use regular 80W90 non-synthetic you'll save some money, but you need to be changing it every couple of years (and it's not a fun job having to remove and replace/reseal the diff cover).

I have to disagree with the opinion that if you use non-synthetic gear oil your diff will wear out. Synthetic oil is better and has a much longer change interval, but before synthetic oils existed it's not like differentials were blowing up every 50k. I put 80W90 in my POS Sport Trac after it broke an axle and I lost the $60 worth of fresh synthetic I'd recently put in it. Good enough for an SOHC V6 w/200,000 miles on it.

As far as the owners manual saying the synthetic is "good for life" well 100,000-150,000 miles is probably what they consider to be the life of a vehicle. Change it.
 




Mbrooks420

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As stated above, it's your truck. It's supposed to have synthetic. If you aren't going to use the right stuff, why change it at all?
 




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