what gear oil do you guys use?

me32

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bumping this thread to see if anyone else has recommendations.
Looking for anything in particular?

For the ford LSD i like royal purple and the added ford friction modifier.

My other choice would be amsoil with ford friction modifier

3rd is Mobil 1 with ford friction modifier
 

Race Red Boss

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Looking for anything in particular?

For the ford LSD i like royal purple and the added ford friction modifier.

My other choice would be amsoil with ford friction modifier

3rd is Mobil 1 with ford friction modifier

Thanks, those choices seem to be a pretty popular recommendation. My 08 came with an LPW diff cover and 3.73 gears.
 

merkyworks

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Do you really need to add the friction modifier when using RP gear oil? RP gear oil already has friction modifiers added into it from the factory.
 

RBB

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Do you really need to add the friction modifier when using RP gear oil? RP gear oil already has friction modifiers added into it from the factory.
I’ve added the RP both with the additional FM and without it. Noticed absolutely no difference either way. No additional noise from the diff without it.
 

cidsamuth

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So, we just got into an argument about this on the S197 forum. I wrote RP about whether FM was needed, and they wrote be back immediately to say:

"Thank you for contacting us. You should not need any additional friction modifier additive with our Royal Purple Max Gear 75W-140 (part #01301, quart bottle) in your 2008 Ford Mustang’s limited-slip differential.

All of our Max Gear oils contain an appropriate dosage of the friction modifier additive that for most OEM and aftermarket performance type limited-slip differentials, no additional friction modifier additive is typically necessary. It is rare that any additional LSD-FM (limited-slip differential friction modifier) would be needed with our Max Gear oils. Please keep in mind that LSD-FM actually takes away LSD clutch grip, which allows the clutches to release more smoothly on tight turns. A large over dose of the LSD-FM additive is not desirable as it could reduce the effectiveness of your limited-slip differential unit's operation (possibly result with “one-wheel peel”).

If a customer experiences a shudder on tight turns after doing a limited slip differential fluid change to our Max Gear oil, we will recommend taking the vehicle to a nearby empty parking lot and doing a couple of sessions of 10 slow and tight as possible figure 8s. The figure 8 procedure is often standard practice at car dealership service departments for limited-slip axle/differential oil changes. This works the fluid in between the clutches, and treats them due to the high differential in the wheel speeds. This normally will make the shudder in a limited slip differential that is in good mechanical condition go away.

If you are still experiencing a shudder on tight turns after doing the sessions of figure 8s and some normal driving, then you may need to add a cap full or two of some additional friction modifier to stop the shudder. Don’t dump the whole bottle in though, as you already have what is considered a normal limited slip differential-friction modifier dose for most applications. Limited slip friction modifier can be purchased at your local Ford, GM, Jeep, Dodge or Chrysler dealer parts departments or bought from a local parts store, they are all basically the same stuff. Remember to repeat the figure 8s each time limited slip friction modifier is added, if you do need to add any additional friction modifier.


Thank you for inquiring about Royal Purple, and have a great day!"
 

Race Red Boss

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So, we just got into an argument about this on the S197 forum. I wrote RP about whether FM was needed, and they wrote be back immediately to say:

"Thank you for contacting us. You should not need any additional friction modifier additive with our Royal Purple Max Gear 75W-140 (part #01301, quart bottle) in your 2008 Ford Mustang’s limited-slip differential.

All of our Max Gear oils contain an appropriate dosage of the friction modifier additive that for most OEM and aftermarket performance type limited-slip differentials, no additional friction modifier additive is typically necessary. It is rare that any additional LSD-FM (limited-slip differential friction modifier) would be needed with our Max Gear oils. Please keep in mind that LSD-FM actually takes away LSD clutch grip, which allows the clutches to release more smoothly on tight turns. A large over dose of the LSD-FM additive is not desirable as it could reduce the effectiveness of your limited-slip differential unit's operation (possibly result with “one-wheel peel”).

If a customer experiences a shudder on tight turns after doing a limited slip differential fluid change to our Max Gear oil, we will recommend taking the vehicle to a nearby empty parking lot and doing a couple of sessions of 10 slow and tight as possible figure 8s. The figure 8 procedure is often standard practice at car dealership service departments for limited-slip axle/differential oil changes. This works the fluid in between the clutches, and treats them due to the high differential in the wheel speeds. This normally will make the shudder in a limited slip differential that is in good mechanical condition go away.

If you are still experiencing a shudder on tight turns after doing the sessions of figure 8s and some normal driving, then you may need to add a cap full or two of some additional friction modifier to stop the shudder. Don’t dump the whole bottle in though, as you already have what is considered a normal limited slip differential-friction modifier dose for most applications. Limited slip friction modifier can be purchased at your local Ford, GM, Jeep, Dodge or Chrysler dealer parts departments or bought from a local parts store, they are all basically the same stuff. Remember to repeat the figure 8s each time limited slip friction modifier is added, if you do need to add any additional friction modifier.

Thank you for inquiring about Royal Purple, and have a great day!"

Very timely info. Thanks for posting!
 

me32

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Do you really need to add the friction modifier when using RP gear oil? RP gear oil already has friction modifiers added into it from the factory.

For my personal taste i use friction modifier with RP
 

Race Red Boss

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I changed out the diff oil today on my 08 w/LPW diff cover using Royal Purple 75W140 and Lubelocker gasket.

I put nearly 3 qts. of the RP in, but did not leak out the diff fill hole. Anyone know what the fill capacity is with the LPW diff cover? I'm sure it must be close to full....
 

Catmonkey

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Since it only calls for a little over than 2 qts. I'd say you overfilled it. What fill hole are you referring to? The correct fill hose is on the driver's side of the differential housing.
 

Race Red Boss

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Since it only calls for a little over than 2 qts. I'd say you overfilled it. What fill hole are you referring to? The correct fill hose is on the driver's side of the differential housing.

The fill hole on the drivers side.....rear of the diff housing. I think the LPW diff cover expands the capacity, and given no fluid leaked out the hole....have to believe that's true. I even raised the car up further to ensure it wasn't tilted downward....and still didn't leak out any fluid.

Going to give LPW a call Monday to see if they know the capacity.
 

Catmonkey

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Adding oil above the fill line is likely to puke gear oil out of the differential when the oil heats up. Typically expanding capacity doesn't elevate the OEM fill line, but increases the volume of oil up to that point. The fill line is about an 1" below that plug you're relying on. My suggestion is to remove the side plug and let it drain to the correct level and wipe off the excess oil from the axle. The oil will come out one way or another.
 

Race Red Boss

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Adding oil above the fill line is likely to puke gear oil out of the differential when the oil heats up. Typically expanding capacity doesn't elevate the OEM fill line, but increases the volume of oil up to that point. The fill line is about an 1" below that plug you're relying on. My suggestion is to remove the side plug and let it drain to the correct level and wipe off the excess oil from the axle. The oil will come out one way or another.

I thought the procedure was to fill until the fluid started to run out of the fill hole? Can you also tell me where the "side plug" is located?

Thx.
 

nxhappy

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from the tests I have seen, royal purple is shit. I would say mobil 1 or amsoil hands down
 

SCGallo2

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I thought the procedure was to fill until the fluid started to run out of the fill hole? Can you also tell me where the "side plug" is located?

Front side of differential, driver's side. Fluid level should be level with the bottom of this fill plug, regardless of what differential cover you have installed.

Diff Fluid Fill.jpg
 

Catmonkey

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Because the fill hole is intended to gauge the oil level based on the pinion bearing, quantities can fluctuate depending on application. 4.25 pints comes out of the GT500 owner's manual. On a truck, the pinion is angled higher than the mustang and might call for more fluid. Just take the plug out of the location shown above near the pinion and let it drain any excess, replace and you're done.
 

Race Red Boss

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Because the fill hole is intended to gauge the oil level based on the pinion bearing, quantities can fluctuate depending on application. 4.25 pints comes out of the GT500 owner's manual. On a truck, the pinion is angled higher than the mustang and might call for more fluid. Just take the plug out of the location shown above near the pinion and let it drain any excess, replace and you're done.

Thanks. The location circled in SCGALLO2 diagram was the hole I used to fill the diff. I'll report back what LPW has to say about the capacity of the diff with their cover. On their site it simply states....increases capacity.
 

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