Diff Questions

[BlueF350]

I am new to Ford F350s, biggest thing I had before was a Toyota Tundra. I have a few questions about changing out the fluid in the rear diff.

1) I asked the local Ford dealer the interval for chaging the fluid out and they said they did not have one. I am hoping some one can tell me what they recommend. I do tow with it but not that often and then it is pretty light (under 6,000lbs).

2) I know the rear diff take a synthetic gear oil. Getting recomendations of what to use would be nice but i would also like to know how to tell if a certain type meets all of Fords specifications. It is just wieght or is there something else I also need to look for?

Thanks,

Aaron

[SmokeyWren]

Originally Posted by BlueF350

1) I asked the local Ford dealer the interval for chaging the fluid out and they said they did not have one. I am hoping some one can tell me what they recommend. I do tow with it but not that often and then it is pretty light (under 6,000lbs).

Your Scheduled Maintenance Guide states the rear diff is lubed for life and does not ever need inspection or changing if you do not get water in it. And it's pretty hard to get water in it if you don't ford rivers deep enough to get water over the vent tube.

However most truck enthusiasts change the rear diff lube every 3 or 4 years, and some like me every 100,000 miles or so.

2) I know the rear diff take a synthetic gear oil. Getting recomendations of what to use would be nice but i would also like to know how to tell if a certain type meets all of Fords specifications. It is just wieght or is there something else I also need to look for?

Assuming your F-350 has single rear wheels (SRW), then just so it's full synthetic gear oil and SAE 75w140 that meets API GL-5 specs. Brand doesn't matter, as long as it's full synthetic, such as Royal Purple, Redline, Mobil 1, or even Wal-Mart's house brand = SuperTech or some such.

For example, Valvoline makes a full synthetic gear oil. It comes in SAE 75w140 and meets API GL-5.
Valvoline SynPower gear lube

If you have a "real" F-350 one-ton dually with dual rear wheels (DRW), then you have a different rear axle that requires 75w90 synthetic gear lube. However, Ford has advised their dealers that it's okay to use the 75w140 gear lube in those too.

[GrampyJim]

Smokey, the 75W90has been superceded in the Ford system. 75W90 is no longer available (in Motorcraft packaging) and 75W140 is the new requirement for rear axles. IIRC, the advice came in an SSM (special servicemessage) - Ford has made these nearly impossible to search... making it necessary for you to just trust me...

FWIW, stepping "up" in lube isn't usually a problem (though I have read that synthetic gear oil isn't as water friendly as conventional oils... but let's remember that synthetic base stocks MAY play a roll there - be they hydrocracked or PAO). Stepping "down" in lubes may be a concern depending on the gearset... We see gearsets with different angles, pitches, what-evers as the engineers strive fornoiseless operation or other desirable traits... in some cases, synthetics may be a means of improved fuel consumption numbers or may be required for shear stability or other reasons depending on the cut of the gears.

Sorry for the long winded post... it can often be difficult to determine where too much info becomes not enough info....

[SmokeyWren]

Originally Posted by GrampyJim

IIRC, the advice came in an SSM (special servicemessage)

You've mentioned that before, but the workshop manual as late as January 2009 still had the requirement for
"Motorcraft 80W-90 Premium Rear Axle Lubricant XY-80W90-QL (US); CXY-80W90-1L (Canada)"
for the (for example) 2005 Dana 60 front axles and
"SAE 75W-90 Synthetic Axle Lubricant XT-75W90-QLS"
for the 2005 Dana 80 rear axle

And my 10-year-old Owner's Guide says 75w90 synthetic gear oil in both the Dana 60 and Dana 80 axles.

And right now, today, the current Ford Motorcraft quick reference guide calls for SAE 90 Hypoid Gear Oil in the front axle.
http://www.fcsdchemicalsandlubricant...f/axlelube.pdf

So apparently even Ford doesn't know the "right" answer as to which gear lube to use in a Dana axle. But if it were my truck, I'd probably stick with synthetic 75w90. It's included in that latest quick reference guide, so apparently some Ford techs are still able to get it.