What diff lube should I use?

[05stroker]

Going to change my diff fluid Should I use Amsoil or Royal Purple 75w140?

[topdwg]

I'd stick with OEM. It's full synthetic too...

[smokersteve]

I use amsoil, look at my sig

[scotty2280]

i used ams oil, i dont think it really matters as long as its at least oem.

[PGreenSVT]

I would use Amsoil before the RP any day.

[Tony V]

Im using royal purple and will keep using it.

[cartmanea]

Amsoil Severe Gear is very good stuff. I used RP when I changed gears, but next fluid change will be to Amsoil.

[PGreenSVT]

I have seen some test results that really don't favor the RP. I put RP in my Mustang recently when I rebuilt the posi and swapped to 4.10 gears but I am going to drain it and switch it over to Amsoil.

[cartmanea]

Probably the same test I saw that showed Amsoil Severe Gear winning every test by a large margin. The test was performed by Amsoil though, so who knows. It does seem like a good product though. The RP didn't do as well because its viscosity is lower (hence their MPG claims) and it didn't protect against corrosion very well.

[smokersteve]

Another thing is that ams is cheaper than royal purple. Especially with their preferred customer program. Even with the first purchase it is still cheaper than RP