How many qts does the rear diff hold?
What type? Is there an additive?
​​​​​Diff has always made a whine noise when acceleration. When u let off gas it goes away.
No sure how much or what i used last time.
Rear diff has 317k miles on it.

 

man we're in the same situation. I have the same questions and my van has 313,000 miles...

I bet the whine noise is normal though. The cargo area somewhat amplifies it. Like a school bus. Remember the differential whine in those?

 

You've asked a real open end questions.

Lets start with how much cause its the easiest. The are approximate fill quantities in every owners manual, but they are approximate. Take the fill plug out and fill until the until oil starts coming out of the fill hole. Be on a flat level surface.

Type is bigger issue, There are 3 different types Mineral, semi-synthetic and full synthetic. Is and open differential or limited slip? So viscosity range is what I think you're asking.

I would take the cover off and completely drain the diff. and inspect for metal shavings, and check backlash. You need dial indicator for that step.

If it is a real bad howl I would use mechanics bluing and check pinon to ring gear contact. Contact area between the pinion to ring gear should be pretty much in the center of the ring gear and pinion,

The only way a diff can get low on oil is to be leaking, because howl can come from just being low on oil.

So back to viscosity range, if the backlash is at the top end of the spec I would use a higher viscosity semi synthetic like 85w140, If the backlash is in the middle of the spec I would use the viscosity Ford/ Sterling/ Dana recommends. On an open diff the go to viscosity is usually 80w90 mineral on a limited slip it can very easily. You will be looking for an API GL rating of 4/5 from the manufacture of the differential. That GL rating will confirm add-pack you require.

If the contact area is wrong or the backlash is out of spec I would fix that first.

API= American Petroleum Institute

Sorry you'll have some research to do, because of limited information on which diff you're dealing with does matter for the lube you need.

 

That is not normal

 

I know about the whine, bought a Dakota that did it, was a burnt ring gear BUT my 99 E350 did this for 12 years, transmission was rebuilt, case was cracked, so I got another case, the rebuilt guts from mine placed in it, there hasn't been a noise since, but mine did it from purchase with 73,000 miles on it.

 

vetex2 is correct and a bad wear pattern, along with the whine (the result of incorrect gear setup) becomes permanent at some point, you can't adjust it out. If the noise is too bothersome you'll need new ring & pinion gears not to mention carrier and pinion bearings. Naturally you need a shop to set gear depth and backlash. $$$ A junkyard may be your best option with something under 100k miles.