10.25 rear oil change

[ghunt]

I've asked this in two different places and never gotten a straight answer.

What oil do I use in the rear on my truck, what friction modifier do I need (and how much), and on the diff cover is it better to use a paper gasket or silicone?

 

[hesutton]

75W-90 gear oil with Motorcraft friction modifier.

You will be just fine with silicone.

Heath

 

[ghunt]

Well, I actually already bought a paper gasket before I even thought about the silicone.

Is it more likely to leak sooner with a paper gasket?

Also do you just use the 4 ounces of the friction modifier?

 

[Fishin76]

If installed right, the paper gasket would be fine. The paper gasket is not as forgiving if you just tighten all the bolts in a circle, rather than do a chris cross pattern. You can get away with doing a circle pattern with the silicone, it will squeeze into the spots that may bow out when do it that way. If you do tighten in a circle, start at the top, that way, if there is a leak, it will be on top of the diff, higher that the level of the fluid. Also, I apply the silicone to the cover, so that I can position the cover easier with out disturbing the silicone to0 much.

 

[hesutton]

Well, I actually already bought a paper gasket before I even thought about the silicone.

Is it more likely to leak sooner with a paper gasket?

Also do you just use the 4 ounces of the friction modifier?

I'd put silicone on both sides of the paper gasket. The ratio of the friction modifier escapes at this time. But, it will be a ratio of X number of ounces fo modifier for X number quarts of gear oil. It will certainly be on the bottle.

Heath

 

[ghunt]

Should have asked earlier: Does the diff take 3 quarts, I saw that posted somewhere else, just wanted to check.

 

[1994IDI]

I used Lucas 75W-90, 7 oz. of friction modifier, and a paper gasket and silicone. It held about 3 1/4 quarts of gear oil, plus the friction modifier.

 

[ghunt]

Could I use a synthetic blend in the rear or does it have to be full synthetic?

 

[Diesel Max]

Could I use a synthetic blend in the rear or does it have to be full synthetic?

I used standard 75W 90 with 6 oz of friction modifier. You can use synthetic if you wish and want to spend the extra $$$. Ford does not call for synthetic in their 10.25's according to my service manual. I have seen many a post on here of folks using either regular or fully synthetic. I would think a blend sythetic blend would hurt it either way.

 

[ghunt]

OK...somebody had told me they came from the factory with full synthetic, I didn't really know.

 

[Diesel Max]

OK...somebody had told me they came from the factory with full synthetic, I didn't really know.

From the documentation I have found the 10.25 did not come from the factory with synthetic. It came with regular oil and friction modifier added.

The Ford F150 with 8.8 ring gear and 4.10's did however come with synthetic gear oil and friction modifier.