1970 plymouth roadrunner gear oil

[Nick zenchak]

Hey fellas,
I have a 1970 plymouth roadrunner with 391 gears and 8 3/4 posi rear. I was wondering if anyone had an idea of what type of gear oil i should be putting in it?
Thanks

 

[cosgig]

I believe the OE is 80/90, although synthetics are available for it as well! If you're considering the use of synthetic, I believe you have to completely drain the case before refilling with synthetic, and don't forget a bottle of friction modifier for the SG unit!

 

[Nick zenchak]

I believe the OE is 80/90, although synthetics are available for it as well! If you're considering the use of synthetic, I believe you have to completely drain the case before refilling with synthetic, and don't forget a bottle of friction modifier for the SG unit!

Thanks for the info!