Rear Differential Oil specification for '92

[strikefast]

I have a '92 Explorer, and my rear differential cover gasket is leaking. I'd like to take off the cover, fix the gasket, and refill it. However, I can't figure out what viscosity of gear oil to use.

My door jamb label indicates axle code 41. According to this link, that means I have a 3.27 axle ration (open):
http://www.explorerforum.com/ntrprize/Axle.htm
Not a limited-slip model--guess I don't have to worry about friction modifier...

I also looked for a tag around the axle specifying the type of oil, but couldn't find one. I could only find a metal tag hanging off of one of the differential cover bolts, with letters/numbers I don't understand:
S622B
3 27 88 1K23

(Well, after reading around the site, I now understand the 3 27 88 portion)

Is there somewhere else specific I should look around the axle/differential? For now I'm thinking there's not, so I'm turning my attention to the following:

The Ford owner's manual says:
Part Name: Hypoid Gear Lubricant
Part No: XY-90-QL or E0AZ-19580-A
Specification: ESP-M2C154-A

Autozone's repair info website simply says "90". Does that, coupled with the first Ford part number above, imply a straight 90 viscosity oil? Does anyone make straight 90 anymore?

Would using 75W-90 Mobil 1 Synthetic (I like Mobil 1) or some other 80W-90 oil (synthetic or conventional) be the thing to do?

Castrol Hypoy C 80W-90 seems to mention the Ford specification above (only reference to it I could find online from gear oil data sheets).

 

[ma96782]

Would using 75W-90 Mobil 1 Synthetic (I like Mobil 1) or some other 80W-90 oil (synthetic or conventional) be the thing to do?

Either will do.

Aloha, Mark

PS......Dino....spec, API, GL-5, SAE 80W-90.....is common.

 

[strikefast]

I ended up going with the Mobil 1 75W-90. Removing the spare tire made this job a LOT easier for me, particularly when accessing the fill plug. After loosening the bolts, I broke the old gasket seal using a putty knife and let it drain. I completely removed the cover and spooned the remaining oil out of the differential housing where it collects right behind the lip (maybe a cup or so?). Cleaning the old RTV from the machined surface of the differential housing was easy with the putty knife.

The absolute hardest part was cleaning the old RTV from the cover itself. I spent over an hour with the putty knife trying to get it all out. I didn't want to shortcut this part, though, for fear of creating a poor seal with the new gasket material.

I cleaned the magnetic fill plug, and also the magnetic bars embedded near the bottom of my plastic cover. Then, I cleaned the mating surfaces to make sure there was no extraneous oil remaining.

I used Permatex Ultra Copper Gasket Maker for the new gasket. Made a bead around the groove in the cover, stuck it on, torqued the bolts down, and let it sit empty for a couple of hours to cure before refilling with the Mobil 1. I bought a short piece of 1/4" fuel line (~18in. long) which I used to refill the differential. 5/16" probably would have worked, too, and helped the oil flow easier/faster, but I didn't want to risk it not fitting inside the fill hole and I didn't have exact measurements when I bought it. Anyway, there's plenty of space above where the spare tire normally sits to elevate a 1qt. bottle of oil, hook it to this short piece of fuel line, and let it flow through the hose to the fill hole. For me, it took just about 5.5 pints to get it within ~1/2" of the bottom of the fill hole.

I think Ford started using a metal cover the next year. I think I know why--my cover was cracked right through one of the bolt holes on the lower side of the cover. Looks like someone overtorqued a bolt in this cover's past (not me, this is my first time). I tried to find a new cover locally to no avail. It could only be ordered, and I needed my '92 back on the road! Fortunately, I spotted the crack before RTV'ing the cover back on the differential. I used some of the RTV to coat the inside and outside of the cover in the vicinity of the crack. I would've preferred a new cover, but oh well...

So far, no leaks after a couple hundred miles of driving (knock on wood). I don't think I'll bother with a new cover at this point, unless a leak appears in that area.

 

[ma96782]

Some folks have been known to crack or dislodge the rear end cover by using a jack on the "pumkin." The jack touches the cover (or all the weight on the cast rear end) and when lifting the rear end.....viola.....a leak develops.

I'm guilty.......though, most manuals will tell you to lift only one side at a time.

Aloha, Mark