Ford 450 Rear Differential Leak Help

Also make sure axle vent is clear.

Should be on one axle tube or the other.

Have seen many recurring leaks because of plugged vents.

Dave

https://www.fcsdchemicalsandlubricants.com/main/quickref/axlelube.pdf

You might want this print out and take with you shopping. I already posted above but later in the night was trying to find normal temps for wheel bearings and ran across this, it might help you.

Where I get Ford parts at 1 part guy is really good and another guy sometimes can't find his own head, so look my own stuff up as much as possible.

The diff could be a Dana S110 or the Dana 80, the S110 has no rear cover just the front like the Ford 9" if that's the case the bolt at the 6o'clock position is the drain plug, after draining you will need 5qts that's what my F450 took. The owners manual called for 7 qts.
75-140 Synthetic

You CAN get a differential cover gasket if you wish. Many if not most now just use RTV "gasket maker" like Permatex Ultra Black. Either way, be sure the holes in the cover aren't dimpled before you install it.

x2 on checking the pinion seal. Had ours done a couple of years ago, about $30 for the seal, 150 for 5 litres(qts) of gear oil and 5 hrs labour $450. Next oil change, the shop found it leaking again, fixed under there 1yr warranty, our cost $0.
Only explanation for the first problem was possibly lack of use, second was put down as a defective seal.

The oil was a very small leak running down from the pinion at the front and then off the bottom near the rear cover.

Beverley and Ken

Be sure there is not a leak at the pinion seal.

When you pull the cover be sure the bottom edge has not been dinged from anything hitting it. If you can let it sit overnight it will drain completely and not be weeping on to the sealing surface when you are assembling. If you use a wire wheel on it be sure it doesn't throw any wire bristles into the gear area. Wipe the housing out good just before you put the cover on so it doesn't weep onto the seal surface.
You also want to use brake cleaner or other solvent to strip the surfaces clean for good adhesion. Use an automotive black, red or ultra blue silicone.

Thanks for all of the help. I will be attempting this repair this coming weekend. Thanks again!

Yes, the MObile1 Full Syn 75w140 is good stuff. That's what I run as well. Keeps temps about 30F cooler than other synthetic lubes (I have a diff temp gauge because I run so heavy, up to 25k pounds combined).

Should be a plug on the side , just unscrew it and put fluid in untill it starts coming out .

Be careful undoing the bolts. On one of the bolts you might have what looks like a small metal tab with some numbers stamped on it. That is the "axle tag" and comes in handy for looking up info on diff.

as example see http://www.fordification.com/tech/rearends_ford01.htm but you'll have to find newer site that covers your year model.

google "ford axle tag decoder" Come in handy to know what you have (type and amount of oil, torque etc)