I know I should've probably kept this one in my forum, but I wanted to bring to you guys. I just did the rear differential fluid in my 1999 Expedition. It calls for Ford synthetic 75w140 gear lube. I used that, but of course it's leaking now (there wasn't a gasket there to begin with, and I thought I did a good job of sealing it. Anyhow, I'm not too keen on buying another 3 qts. of this lube (it's like $25 a quart ) Anyhow, I just want to know if I absolutely have to use 75w140, or if I have a little bit of leeway. I'm thinking I'd rather go with Mobil 1 or Redline, but neither offer something to match the Ford stuff exactly. Any thoughts?

Thanks!

XXL

 

I wouldn't claim to be an expert in this area, but I do feel that the viscosity specification is probably important. It would seem that if it made little or no difference, it would be much easier for Ford to go with the more common grades.

I do believe, however, that Mobil 1 IS made in 75W140 viscosity, though you may not find it stocked much. Also, if you ask nice (or threaten to go elsewhere), you can usually get your Ford dealer to discount this kind of item. You can also try Fordpartsonline.com, although they might not be able to ship "hazardous" liquids like this.

Too bad about the leak. Do you think you refilled it maybe a little too soon? I'm putting an SVO cover/carrier support on mine and hope I don't have your problem.

Good luck!

 

I replaced my differential oil with Redline 80w140 full synthetic @ $8.00 a quart.Also used FelPro part # RDS 55341 differntial gasket.I dont trust just using RTV to seal the cover.

 

Yeah probably - I put the RTV on the diff cover, and let it sit for about 10-15mins, then stuck it back on there, torqued it down, and refilled. In retrospect, I should've let it sit until it started to skin over, then stuck it back on, gotten lunch, watched some TV, then refilled. All well - lessons learned.

As far as the viscosity goes - I'm not too concerned with the cold weight. Seeing as how the Ford stuff is 75w140 and the Redline is 80w140, it would appear that the Redline stuff will just be *slightly* thicker when it's cold out, even though the Ford stuff will easily hit the 80W mark within a mile or two down the road. In other words, since the end product is same, and the two weights are so close, I won't sweat it. Especially not in Maryland - it gets pretty hot, but not too terribly cold.

Thanks for the input, though!

XXL

 

So far, all I've found in 75w140 is Royal Purple and Amsoil. I think the Redline stuff is going to offer the best bang for the buck. Also, a friend told me about something called "The Right Stuff". Apparently it's the gasket sealant that's used for heavy duty trucks (like dump trucks, 18 wheelers, etc.) and it's ultra heavy duty.

Also, does anyone know what the drain interval is for the rear differential on my truck? My mom's 1998 Explorer manual says the rear lube never has to be changed - ever. I decided to change mine just because I bought the truck used, and I like to know what's going on. If the interval is kinda low, should I install one of those drain plug kits on the differential cover (providing I have clearance)?

XXL

 

Ford claims 100k mile change intervals;but they also say that about the plugs too,but we all know better! If you want just pull the fill plug and siphon it from there.Do you have the 8.8 differential? If so,use FelPro gasket #RDS 55341.

 

Well, as far as changing the fluid. If you use your truck for heavy towing, or go off-road often, you want to change it once a year. If you do neither of those every 35,000 miles is good!!

Also, next time you change the fluid why don't you buy a gasket? They are only a few bucks. That RTV crap never works.

P.S. I beleive the expeditions have the 10.25 rear axles.

 

I don't do heavy towing, but I don't mind coughing up a few bucks now and then to save money in the long run. I didn't get a gasket because I had heard from numerous sources not to use one, and there wasn't a gasket when I took it off. I think it's the 8.8 LS axle, although I'm not sure - I remember seeing 8.8 somewhere on there. I'll double check

XXL

 

The reason there wasn't a gasket was because, it's cheaper for the factory just to put RTV. A gasket is always the best way to go in my opinion!!

 

Duly noted - I knew there had to be some sort of money-saving function for the FoMoCo

XXL

 

I had the same problem...TWICE. I changed the rear diff on my supercrew to royal purple. Then after 4,000 miles it leaked. I changed it again, and after about 4,000 miles it's leaking again! I didnt use a gasket either time. Now i'm going to use a gasket. But do you need to put the gasket sealer on there too or do you just use the gasket?

 

75W-140 synthetic seems to have replaced 80W-90 dino as OE rear axle lube at Ford and GM, maybe Dodge also. The axles are identical, just that the syn is considered "lifetime".

The local PepBoys has both Mobil 1 and RP in 75W-140. The Mobil is much more expensive. I use Redline gear oils, not on price only, but also because it really does contain limited slip additive (also available without). When I tried the M1 gear oil, the LS unit chattered.

Jim

 

Normally, you use either the gasket (rubber) or the gasket sealer (RTV), but not both. For cork, you may use some brush on, or spray on sealers.

In any case, no matter what you do, you need to clean both surfaces. That's especially important with gaskets.

For whatever it worth, I used Ultra Blue RTV last time (30,000+ miles ago) and as far as I can see, there's not a drop of oil that leaked from the rear end.

 

I looked all over for a gasket. I even called a dealer, they said that for 03 they only use the silicone. I used Ultra Black, it's the high temperature one. I just did it again tonight but i'm letting it set up over night before i put the lube in. I'll see if that makes a difference this time. On this tube it says to finger tighten the nuts until the sealant starts to come out the sides. Wait an hour and then tighten the bolts and additional 1/to 1/2 turn. So thats what i just did this time. This better work this time.

 

I am needing to change the oil in my rear end. The other night I checked out the rear end to see if I have a drain hole......well I don't. I have the limited slip, so I'm glad I have to take the cover off to drain it so I can make sure everything is ok inside.