What gear oil to use?

[gfrease442]

I have a 1990 Mustang LX 5.0L with the 8.8 rear end. I have to change the gasket in the differential cover, because of a leak. I don't know what gear oil to put back into the differential once I change the gasket. I want to put the Royal Purple 75W-140 synthetic, but I'm not sure if that would be the right oil. Also, do I have to put the friction modifier in the Royal Purple 75W-140 synthetic gear oil? Is 75W-140 the right gear oil?? Or is some other weight gear oil better?????? Any input would be appreciated. Thanks

 

[Mavrick]

I went with Royal Purple 75-90, it had friction modifier in it already.. the product should tell you on the bottle whether or not you need to add friction modifier.

 

[tjm73]

Any name brand 90 weight will do. Almost all name brand hypoid gear oils have the friction modifyer in it. Just look for it onthe label. I use Valvoline any time I'm in my diff. Don't get the old stuff on any clothes you like. It stinks bad and it will never, ever, stop stinking if you get it on your clothes.

 

[maverick0716]

I use Redline 75W90 in mine. Most synthetics already have the friction modifier in it.

 

[Duro5341]

Castrol...........80W-90 hypr.......bah, bah
it's ceritifed to use in our posi rear ends
also buy the fristion modifier from FORD, it's like $5.00

Duro

 

[Shakerhood]

Ford Service Manual calls for 80W-90 with Friction Modifier