Rear diff

['14SHO]

Whats everyone’s preference on rear diff fluid? What weight etc. I’ve got some valvoline full synthetic 75w140 from flushing the PTU. Would that be appropriate or is there a better option. Cars at 26k so just wanting to get all of this the way I want it

 

[Choppa]

80w-90 for Rear Diff

 

[krewat]

Do they spec synthetic for the rear diff? Reason I ask is, over the years, Ford had changed their spec for the Sterling 10.25/10.5" diff from 80w90 to 75w140 synth. Turns out, they were burning up the front pinion bearing, it seems (seen that a lot on 8.8" diffs too, where they use an NTN bearing for the front pinion bearing, but Timken on everything else - NTN bearing gets black over time).

Not that this has any bearing (pun intended) on the current discussion

 

[Choppa]

Do they spec synthetic for the rear diff? Reason I ask is, over the years, Ford had changed their spec for the Sterling 10.25/10.5" diff from 80w90 to 75w140 synth. Turns out, they were burning up the front pinion bearing, it seems (seen that a lot on 8.8" diffs too, where they use an NTN bearing for the front pinion bearing, but Timken on everything else - NTN bearing gets black over time).

Not that this has any bearing (pun intended) on the current discussion

 

['14SHO]

Didn’t realize they actually had it listed lol. I don’t know if the 75 140 would be better or not

 

[SHOdded]

If you compare viscosity behaviour and it is similar between the two products, sure go right ahead. But it won't be. Stick with 80w90 or 75w90.

Now if you switch to a product like Redline Lightweight Shockproof, maybe could be used in both PTU and RDU. But I know of only one person doing that so far.