Rear diff empty but not leaking?

[Mommystrucky]

About 3 weeks ago I started hearing a whine and figured it was the front driver side wheel bearing again. Sounded like it at least, drivers seat was where it was the loudest. It got progressively louder every time I drove it. Took it to my mechanic yesterday and he put it up on the lift checked the front bearings and they were good, he says the noise is coming from the rear diff. He opened the drain plug and it was bone dry. He is completely puzzled because there is no evidence of a leak anywhere and theres no spots in my driveway.:scratch: He refilled it and drove it a bit and says it got a little quieter but still loud. The only thing he can think of is that it got so hot that the fluid evaporated somehow. Is that even possible?

 

[MtrJunkie]

I dont think that's even possible. Oil doesn't usually evaporate, it leaks out of one of the 3 (?) seals, or burns. Sounds like a carrier or pinion bearing is shot.

 

[swshawaii]

^ Ditto. Sounds like time to find a new "mechanic". Evaporated gear lube?

 

[Mommystrucky]

I really dont get it. He put the magnet in there and got absolutely no metal shavings on it. When he opened it up and saw it was empty he stuck his finger in and felt around and it was dry. How does that happen with no leak? He checked everything that could be leaking and came up with no leak. The cover and seal got replaced not even 2 years ago and when it was in for the torque converter earlier this year he made sure it was full.

 

[bry1216]

Look for dirt on inside of rear wheels for maybe it leaked there.

 

[Mommystrucky]

Look for dirt on inside of rear wheels for maybe it leaked there.

I dont even have it, still at the shop.

 

[MtrJunkie]

Something is fishy for sure. Even if the oil leaked out, I dont think it would be bone dry. In order for it to be bone dry you have to clean it out with a fair amount of carb cleaner. 80w-90 oil is a thicker than cold pancake syrup.

I didnt know the 03 explorer came with a rear diff drain plug, but I'm a 2nd gen guy. Maybe the new cover came with one? My transmission guy wont put a cover on with a drain plug because he said that's where they'll leak from first. Especially if the plug gets bumped.

I guess it's possible it got drained and never re-filled at one of your maintenance visits, but I dont think you would have made it more than a week before the whining started, depending on how much you drive.

As bry1216 said, theres only a few places it could leak

1) down the left or right axle shafts toward the inside of the wheels
2) out the drain plug, if there is one on the cover
3) out the pinion seal (where the driveshaft connects to the diff)
4) and of course the cover seal itself.

No offense to your mechanic, but might be time for another pair of eyes to look at it.

 

[Exproblems]

80w-90 oil is a thicker than cold pancake syrup.

I didnt know the 03 explorer came with a rear diff drain plug, .

Just in case you didn't know, the front diff on a 3rd gen Explorer uses the 80W-90 weight gear oil and the rear diff the OP mentioned as the source of the whine uses 75W-140 full synthetic gear oil, along with some friction modifier additive in you have a Limited Slip rear diff. They also have 2 plugs on the rear diff cover plate, one smaller plug on top to fill it with oil and one larger plug near the bottom to drain it from.

 

[MtrJunkie]

Just in case you didn't know, the front diff on a 3rd gen Explorer uses the 80W-90 weight gear oil and the rear diff the OP mentioned as the source of the whine uses 75W-140 full synthetic gear oil, along with some friction modifier additive in you have a Limited Slip rear diff. They also have 2 plugs on the rear diff cover plate, one smaller plug on top to fill it with oil and one larger plug near the bottom to drain it from.

Thanks for the info. I didn't know. I have a 2nd gen.

 

[Bobmbx]

The cover and seal got replaced not even 2 years ago and when it was in for the torque converter earlier this year he made sure it was full.

Yeah. Sure he did. He swears.

If there are no signs of leakage (and if you leaked, you'd see it even if it was 10 years ago), and the diff is empty, Sherlock Holmes would conclude that there wasn't any fluid to start with.

You wouldn't be the first to have a diff serviced and returned to you with no fluid in it.

Evaporated. Never heard that one before.

 

[Bobmbx]

Just in case you didn't know, the front diff on a 3rd gen Explorer uses the 80W-90 weight gear oil and the rear diff the OP mentioned as the source of the whine uses 75W-140 full synthetic gear oil, along with some friction modifier additive in you have a Limited Slip rear diff. They also have 2 plugs on the rear diff cover plate, one smaller plug on top to fill it with oil and one larger plug near the bottom to drain it from.

Ford stopped putting drain plugs on the diffs some time ago. They claim you never have to change the fluid.... ("Filled for life") I believe it says, so no reason to provide a drain.

Neither my '99 Mounty or my '06 XLT have a drain plug.

 

[brendankoch]

Not sure where you got the idea that Ford hasn't put drain plugs on differentials since "some time ago"... It all depends on the design of the vehicle... and on a vehicle with an aluminum diff and independent rear suspension it makes sense have a drain and fill plug. My 2002 explorer has drain and fill plugs, as does any 3rd or 4th gen explorer up to at least 2010 as you can see by the drain and fill procedures listed in the workshop manual for a 2002 as well as a 2010 Ford explorer posted below:

SECTION 205-00: Driveline System — General Information 2002 Explorer/Mountaineer Workshop Manual
GENERAL PROCEDURES Procedure revision date: 08/17/2004

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Axle Check, Drain, and Fill

Material Item Specification
SAE 75W-140 High Performance Rear Axle Lubricant
XY-75W140-QL WSL-M2C192-A

Fluid Check

NOTE: If friction modifier is required, install modifier before lubricant.

NOTE: If fluid is required, replace the original FEHP lubricant with 75W-140. Remove the old tag and install a new tag.

NOTE: When the fill plug is removed, up to one pint will drain from the filler opening.

Remove the fill plug.
Fluid Drain and Fill

Remove the axle drain plug.
Install the drain plug and tighten the drain plug to 34 Nm (25 lb-ft).
Fill the axle to the bottom of the fill plug hole.
Install the fill plug and tighten the fill plug to 34 Nm (25 lb-ft).
Remove the rear wheel speed sensor.
Disconnect the rear wheel speed sensor electrical connector.
Remove the bolt.
Remove the rear wheel speed sensor.

Add one pint of fluid.
Install the ABS sensor.


205-02 Rear Drive Axle/Differential — Ford 8.8-Inch Ring Gear 2010 Explorer, Mountaineer, Explorer Sport Trac
GENERAL PROCEDURES Procedure revision date: 06/11/2009

--------------------------------------------------------------------------------

Differential Draining and Filling

Material Item Specification
Motorcraft® SAE 75W-140 Synthetic Rear Axle Lubricant
XY-75W140-QL (US); CXY-75W140-1L (Canada) WSL-M2C192-A and GL-5

Fluid Drain and Fill

Remove both the fill plug and the drain plug.
Drain the axle assembly.
Clean and install the drain plug.
Tighten to 34 Nm (25 lb-ft).
Fill the axle with 1.65L (3.5 pt) of axle lubricant to the bottom of the fill plug hole.
Clean and install the fill plug.
Tighten to 34 Nm (25 lb-ft).


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