The Differential Difference?

I just brought a '94 Ford Econoline van that was low on diff fluid when I checked it today. It calls for straight 90 weight but after checking around with several parts stores (including NAPA) to no avail, I finally decided to go with some 80-90w they had in stock. How big of a risk am I taking here? Thanks.

Probably not much, I think at this point is why are you loosing fluid is the more important question.

It won’t be a problem. But as suggested, you might want to check for leaks. First the pinion shaft seal, and then pull the rear drums off to check for axle shaft seal leaks.


Is there any way to tell if I have a limited slip differential without jacking up the back wheels? There was a fluid additive recommended for LSDs. Thanks.

`The serial number (VIN) has all the digits for the various items such as engine, transmission, differential, etc. Any dealer mechanic can tell you exactly what the diff. is, ratio whether it is limited slip, etc. If so, you MUST ADD the additive or the clutches will burn out.

None…You say tomato , I say tomAHto.
80w90 IS the 90 weight for that truck.
( It has NO limited slip. See your other post ‘how to tell a 150 from a 250’ )