Technical Correct fluid for 1965 Ford Econoline van rear differential?

Hey everyone, new here. Been restoring a 65 econoline for the past few months, and right now Im swapping out the drum brakes for disc brakes. In order to fully remove the drum brakes, housing, etc, I have to pull out the rear axles, so I figure I might as well drain out the fluid while Im in there and fill it with fresh stuff. Can anyone tell me what weight oil it would take? My best guess is something like a 75w or something in that ballpark, but it would be awesome if anybody knew for sure what the correct answer was. Thanks in advance!

 

75w-90 will work just fine for you.


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And Ford friction modifier if it’s a traction lock.

 

The closest reference I have is for the 1968 Econoline, and it says all conventional diffs use C6AZ-19580-B while all limited slip diffs use C6AZ-19580-C

The former cross references to an 80W90 gear oil, I didn't check into the latter part number.

 

Zoinks Dude! You need the like, owners manual and it will tell you exactly what it wants.

 

75w90 gear oil will be fine. Like others have mentioned; if it’s a traction lock ( I would be surprised) add limited slip additive.


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Thank you all for the info! I have been trying to hunt down a manual for it, but so far no luck.

At the risk of sounding kind of dumb, how would I figure out whether its a limited slip?

 

If the original tag is on the original rear axle, it will tell you if the diff is ltd slip. Among the numbers will be recorded the rear axle ratio.
As an example, a 3.25:1 open diff will be marked 3.25 on the tag.
A 3.25:1 ltd slip diff will be marked 3L.25 on the tag. The L indicates limited slip.

To check manually, put the van in neutral and jack up one wheel. With an open diff, the raised tire (along with the driveshaft) will turn easily.
With a ltd slip, it will be difficult to turn the raised tire since the ltd slip unit will try to turn the tire that's still on the ground.