Changed Differential fluid.

[jfug97]

I changed diff fluid and added 80w90 to my 97 with a D4 rear end. I am amazed at how much of a difference I notice.

 

[Tedybear]

Interesting. We just serviced ours last week. Not sure what the last owner put into it. He did a repair axle bearing that failed and the pumpkin only had maybe a quart and a half left in it. We installed a 'National' OEM bearing and new seals. Axle wasn't scored up or damaged, so I've no idea why someone would use a repair bearing?

Factory tag stated synthetic with the heavier weight fluid. I'll admit, 140 at the top end seems a bit thick. But we'll see.

 

[Robman]

The limited slip rear ends take synthetic w/friction modifier.

The front diff and an open rear diff do not need or call for synthetic.
(but you can still use it)

The front diff calls for a different weight than the rear also.

What's this "difference" you notice with the changed gear oil?

 

[jfug97]

It just feels like it takes off alot easier, hard to explain.

 

[intelisevil]

D4=Limited Slip. It requires 75W140 Synthetic gear oil and 4 ounces of Ford XL-3 Friction Modifier Additive.

Some Synthetics claim you don't need the XL-3 but you DO need the 75W140 Synthetic for your Limited Slip diff.

What made you use the 80W90?

 

[jfug97]

I just wanted to try the thinner oil, I know it calls for 75w140, but some d4s used to use 75w90 and then ford changed it to 75w140. I dont do any towing and added the friction modifier.

 

[drdoom]

I put the thinner oil in too, as I got confused reading the cryptic footnotes in the owners manual. That was 80,000 miles ago and I have yet to put the 140 weight in.

 

[Tedybear]

I think it's fine provided you do not use it for heavy hauling. As for the difference? Well, changing fluid always makes things seem better. If it's a limited slip diff, maybe the friction modifier was wearing out and causing some chatter. New fluid and additive would help cure that.

S-

 

[chefduane]

I used 75w140 Castrol Full Synthetic with the friction modifier. I also put on a shiny new cover and gasket just because. No problem so far.

 

[rb142]

80W90 used to be the spec fluid (still is for the Ranger), and it will be just fine if you aren't towing (and even if you are if you change it now and then). Many of the aftermarket fluids have friction modifier in them already, so it often isn't necessary to add XL-3 in addition. If it chatters, add the XL-3.