I have a 91 sierra and am changing the diff fluids, i will be putting in a synthetic fluid, my question is do i need a special additive as well?


Thanks

I was advised not to put any additive into my diff, however, I did use Mobil 1 synthetic gear lube 75-90. 12,000 miles, no problems yet.

unless you have limited slip with a clutch pack there is no reason to put any aditive in. usually only fords need an aditive, the only reason you should use an aditive is if the clutches chatter while turning.

check your RPO codes in the glove box. If you see a G80, then your truck has a limited slip rear end. it needs the additive. Autozone sells it.