Gear Oil and Modifier

[JIMOCO]

I am putting a new differential cover on my 8.8" solid axel rear end (3.27 ratio). What are your recommendations regarding gear oil? Is the combination of a friction modifier and gear oil better than a gear oil that claims to have a friction modifier added? The car is street driven only, no racing or autoX.

[GFX2043mtu]

Depends on the LSD you are running. My gear type Eaton Truetrak prefers no modifiers. What you will find is that 99.9% of all gear oils have “some” friction modifier in it. Some guys will run it as is but personally I don’t like the idea of not knowing how much. To compound things some off the shelf oils don’t have enough in it for a complete fill rather they are more intended for a top off. The only oil any more I can find with out a modifier in is the standard Motorcraft lube you get from a ford dealer. With a standard friction plate LSD I would go this route and add the exact amount that is called out to it. The The ford stuff is inexpensive and so is the friction modifier. Plus it’s the OEM fluid for the 8.8.

[AC Bill]

I used this product, as it came highly recommended by builders, at the time I was building mine. I did soak the friction discs in the friction modifier before assembly, and still added what was left in the bottle to the diff.

https://www.americanmuscle.com/royalpurple-maxgear-75w140-gearoil.html

[BEAR-AvHistory]

I am putting a new differential cover on my 8.8" solid axel rear end (3.27 ratio). What are your recommendations regarding gear oil? Is the combination of a friction modifier and gear oil better than a gear oil that claims to have a friction modifier added? The car is street driven only, no racing or autoX.

Mine was shipped with a supply of FM with instructions to use it with the gear oil.

[Soulstice]

I used this product, as it came highly recommended by builders, at the time I was building mine. I did soak the friction discs in the friction modifier before assembly, and still added what was left in the bottle to the diff.

https://www.americanmuscle.com/royalpurple-maxgear-75w140-gearoil.html

X2 this is exactly what I do. For heavy or extreme use the FM changes states and is depleted so having some extra in the oil is never bad

[tonywy]

I used Motorcraft 75/140 oil and Ford Motorsport additive. Put the whole bottle of additive in and fill it the rest of the way with the gear oil. No issues. BTW what cover did you get?

[JIMOCO]

Thanks all for your thoughts. I bought a Moser 7106 cover for my 8.8 rear. I had a leak with the old cover and wanted to upgrade to a cover with both a fill and drain plug.