Differential & Transfer Case Fluid

[AP9]

My 2000 Explorer 4WD is going on 179K miles. If I remember correctly, neither the transfer case nor either differential has had the fluid changed. I don't use the 4x4 often, as the vehicle stays mostly on payment, though occasionally it automatically kicks in if the road is slippery. Hasn't really dealt with much worse than grassy hills and deep snow.

I'd like to keep this vehicle going for as long as possible, so I'm assuming it would be a good idea to address this. But it does look like there is (was?) a slight leak at the differential. I don't actually feel any oil, I just see it. Perhaps a brittle/bad gasket?

Does anyone have any recommendations as to what would be a good differential and transfer case oil would be? Should I also replace the differential gaskets while I'm at it?

 

[drdoom]

Use Lucas synthetic in the axles and some DEX-MERC in the transfer case.

 

[AP9]

Ok, thanks. Also how would I know if I have the "conventional" rear axle or the 3.73 or 4.10 that uses synthetic that normally doesn't get changed (per the manual)? For example, a VIN digit or a list of RPO codes?

 

[drdoom]

Door jamb sticker hhas the axle code right on it. Just look there, also look for the axle tag it sometimes has the lube spec on it.

 

[Flash]

The people that came up with "normally doesn't get changed" don't have to live with your vehicle and put up the consequences of insufficient maintenance.
It's cheap insurance to change the diff and transfer case oils occasionally.

The transfer case oil in both my Explorers was black. One has 270,000 kms the other has less but I'm not sure what.

The diff oil was clean and viscous so I left it.

 

[SoNic67]

I don't use the 4x4 often, as the vehicle stays mostly on payment, though occasionally it automatically kicks in if the road is slippery. Hasn't really dealt with much worse than grassy hills and deep snow.

FYI, both differentials and internals in the transfer case are spinning constantly, even when the 4WD is not "engaged". Explorers don't have disconnects at the front wheel hubs.

 

[masospaghetti]

I've had fine results with Mobil 1 Synthetic in the differential.

I would recommend changing the TC fluid - its only a couple of quarts. Get some Mercon V or Redline D4 ATF.

 

[AP9]

Thanks everyone for the advice. I have the D4 limited slip 3.73:1 rear diff.

The manual says:

"Rear axles containing synthetic lubricant
are lubricated for life. These lubricants are not to be checked or changed
unless a leak is suspected or service is required. The axle lubricant
should be changed any time the axle has been submerged in water."

I'm almost 100% certain neither differential has ever been changed. I don't think I've recently been through any water deeper than about 3", though I'm sure I have been in the past. It's not giving me a problem functionally, but it does appear there could be a slight leak -- it's not actually wet to the touch though.

Anyone familiar with TCI Auto ATF? It's kind of on the pricey side (especially the synthetic) but if it's worth the money I'd put it in the transfer case.

 

[SoNic67]

I used in my AWD center differential (called by some 'transfer case') MerconV. Now, when is cold it slightly binds - first time when I move the truck. Then, it probably warms up and stops.
Now I think that Mercon V was not supposed to replace Mercon in any other application except transmissions - like transfer cases, differentials, power steering pumps...

I didn't touch my rear differential.

 

[Lizard]

Redline Synthetic in the diff and you won't need a friction modifier. Also, you don't need a gasket for the diff cover. Just clean the mating surfaces well and make sure there is no old gasket material remaining. Use Blue silicone sealant/gasket maker. Works great.

 

[AP9]

I was just reading some stuff on BITOG and I'm thinking I might put synthetic 75W140 in both front and rear (if necessary) instead of 80W90 in front. This shouldn't really cause any problems, would it? It seems that from the late 90s to early 00s, Ford started recommending 75W140 everywhere they had previously called for 80W90, and the 80W90 standards were actually somewhat flexible then in terms of oil viscosity.