Diff fluid
 

I'm getting ready to do a rear differential seal and was wondering what fluid everyone recomends? And any additive? Thanks

For open (one leg like the front diff), Detriot Locker or Eaton True Track, use the recommended gear lube. For a clutch type limited slip (if your diff tag has an "L" in it or your door tag says factory locker/posi), use gear lube AND a friction modifier for the clutches in the differential. The bottle should say how much friction modifier to quarts of gear lube. Even though it's called a Trac-Lock, it's a clutch type limited slip.

Don't go off the bottle, go off of Ford's recommended amount. Typically the bottles came in a larger amount than required. Too much means your rear end just slips all the time and never locks the two wheels up.

I'm just getting ready to do my rear gear oil, using Amsoil 75W-140, no additive since I've got the one tire fire in the rear.

The AMSOIL has some slip lock in it so even if someone wasn't sure whether to get some or not, you wouldn't have to worry...you'd be covered.

I'd stuff in a Power Tracks Lock Right in your situation. They are easy to install, don't need special lube and make a world of difference in performance over the one leg.

I know, I need something bad. I had a guy that was going to straight up swap me for a factory LSD rear-end... he seems to have fallen off the face of the earth...

Someone recommended valvoline 75w14O synthetic?

I'm 90% sure they are 3:73 ls

Is it a 10.50 axle or a Dana 80? How do I tell?

Dana 80 is on the dually's, all SRW trucks are sterling units, either 10.25 or 10.50.

i went to the dealer and got both front and back fluids and the rear aditive for $100
changed them both
Both were dirty ...changed them out at 190,000 miles:hellox: