REAR AXLE LUBRICANT

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#16

10-14-2011, 10:54 PM

99f350sd

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Gaskets leak The Right stuff won't...Ever. Use both if you like.

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#17

10-14-2011, 10:59 PM

Ford79

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Quote:

Originally Posted by Franko72

No...at least I couldn't find it written on the 5 gal bucket of Castrol syn gear lube that I used in the bosses truck. We added a bottle of Trans-x friction modifier just in case.
I used Mobil 1 syn fluid in my rear axle and I also added Trans-X. Someone, somewhere told me that the oils that claim they have the friction modifier really do not have enough to satisfy Ford.

I was told by the guy I bought my Ford(factory) LS diff from to add 2 bottles of friction modifier even if the oil says it has it. Seems like a lot to me.............

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#18

10-14-2011, 11:55 PM

jc8825

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Quote:

Originally Posted by Ford79

I was told by the guy I bought my Ford(factory) LS diff from to add 2 bottles of friction modifier even if the oil says it has it. Seems like a lot to me.............

You would end up with a "limited grip" differential there.

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#19

10-15-2011, 05:23 AM

knightrider955

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Just did mine. You need to use 75w-130 synthetic. Do not buy a gasket. They dont use one from the factory. I used Ultra Black rtv. Friction modifier doesnt cost that much if you cant find oil that already has it.

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#20

10-15-2011, 09:07 AM

Franko72

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Quote:

Originally Posted by Ford79

I was told by the guy I bought my Ford(factory) LS diff from to add 2 bottles of friction modifier even if the oil says it has it. Seems like a lot to me.............

You are correct... I added 2 tubes of trans-x when I changed my oil. I was told the same thing.

Quote:

Originally Posted by jc8825

You would end up with a "limited grip" differential there.

JC, I thought the same thing, but it's been a good 20k and its still working fine, (still tight).

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#21

10-15-2011, 01:34 PM

jc8825

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Quote:

Originally Posted by Franko72

You are correct... I added 2 tubes of trans-x when I changed my oil. I was told the same thing.

JC, I thought the same thing, but it's been a good 20k and its still working fine, (still tight).

I just put in the Valvoline SynPower Limited Slip with no additive and mine is working just fine as well.

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#22

10-17-2011, 11:18 AM

mikesmayhem

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If too much FM is added it will not allow the LS to work. Even if you add it you should add a little drive around and make sure it is working properly, then add more if it is still chattering. Adding to much FM does NOT make it work better.

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#23

10-20-2011, 03:29 PM

joe_r_dog

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So why do they use synthetic 75-140. That seems like an odd number. And can I get away with something else like 75w-90 on something along the lines of that?? Or does it need what is recommended??

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#24

10-20-2011, 04:02 PM

99f350sd

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For the rear axle it needs to be 75-140 synthetic..Only.

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#25

10-20-2011, 04:35 PM

dchamberlain

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I believe the friction from the limited slip clutches will create too much heat for a 90 weight. 75W-140 will maintain its viscosity better under those severe heat conditions.

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#26

08-25-2017, 09:44 PM

ggazz50

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Quote:

Originally Posted by jc8825

I just put in the Valvoline SynPower Limited Slip with no additive and mine is working just fine as well.

Look at this, Product Information VALVOLINE SYNPOWER FULL SYNTHETIC GEAR OIL W/LIMITED SLIP, Modifier is NOT needed. According to this PDF from Valvoline.http://content.valvoline.com/pdf/synpower_gear.pdf

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