1990 v6 pickup 5 speed, i have the notorious slow leak by the pinion seal of my rear diff. Time for a oil change. Ive been soaking the filler plug for about a week with Pb blaster. I picked up some Amalie Elixir full synthetic GL-5 gear lubricant 75w-90. Is the full synthetic ok to put in such an old truck?
-thanks

 

Well if it's leaking, why. I have been using Lucas gear oil with a mix of 75-90. I like the Lucas products.

 

ok, well its to late to go out and buy that. I just need to know if the stuff i got is fine for the diff.

 

As long as you get all the old out I suppose it'll be alright. I don't run any of the syn stuff. Personally not a fan, Just me though. I know others who like it.

 

There won't be any problem putting full synthetic in, but if it's already leaking why would you. Fix the leak and then put the synthetic in.

 

If you know you have a leak, you're just wasting even more money with every drop of expensive synthetic oil that drips out. Furthermore, it will leak more with synthetic than it is currently leaking with conventional oil. Fix the leak, then consider switching to synthetic.

Also, don't forget to loosen the filler plug before the drain plug.

 

Check and make sure the diff breather isn't clogged..