How often shound the gear oil be changed? My buddy says the oil is synthetic and is good for life

 

no not good for life haha... I think its 60k

 

I think Ford says the rear differential fluid is good for life unless the rear differential has been submerged under water or is being serviced.

 

Subcooled is right.. Also if you are leaking at all.

 

I did mine at 100k. Book says 150k I believe. If you have a LS, it's going to start chattering right around 100k.

 

wait till it chatters the oil ford used and is reccomended is 24$ a quart and i belieave are trucks take a little more than 4 quarts i know because i redid my rear in november....the gear oil is a rip off if you ask me

 

You can buy full synthetic 75W-140 for a lot less than that - no more than $15 a quart. $24 sounds about right for full list price for Motorcraft lube at the dealer.

The 8.8 and 9.75 rears take 5.5 pints (less than 3 quarts) and the 10.25 rear in the 7700 package takes 7 pints.

I don't know how much the LS additive is at Ford, but that's the stuff you should use.

 

I paid $17.50 per quart at the local Ford Dealer last week and $4.00 for Friction Modifier.

 

There is no recommendition to change it at all unless it gets contaminated. I started driving in 1962 and never changed it and never had a problem. Probably over 70 vehicles and some with 200,000 miles.

 

Ok.. I noticed that the front of my Diff is wet. and underneath the truck it loos like it has been splattered with something.

Whats your suggestion?

 

Sounds like your rear pinon seal may be bad. At least that's the problems I was having when I discovered mine was going. Dealer fixed mine under warranty so not sure on cost.

 

I had a rear axel seal replaced under my extended warranty (with $100 Deductable) receipt said total cost was $230 about 50 was from the fluid they had to add

If it were me and I were doing the work I would just buy Royal Purple, no need for the friction modifier if you buy that

 

Thanks Guys.. I plan to do this tomorrow and hopefully get time to take pics.

 

Did mine at 80K and it still looked new, and that gear oil aint cheap either I used the Royal Purple.

 

Depends on the rear axle in the truck. A standard axle will never need to be changed unless it gets exposed to extreme heat (unlikely) or contaminated. I've got trucks on the ranch with standard axles with almost 300,000 miles on the same fluid and it doesn't need changing. If you have a limited slip axle- different program. You should be changing it every 30,000 miles. Not that the fluid breaks down or anything. The issue is the alcohol based friction modifier that is used with the oils. The modifier will absorb moisture out of the air and corrosion is a possibility. If you live in a high humidity area like along the ocean, lakes, etc, you need to be aware of this.