Leaking rear diff at axle seal accompanied by intestifying whine

[Fozzforded]

hey guys. 

While I have been trying to love the 2010 sho I've had a real love/hate with her and unfortunately, we are not on good terms atm...again.   
She has been for sale on/off and now back on again and am trying to make an easy sale but the mileage is just plain scaring most common folks away and just recently presents a sizable rear diff whining noise while driving -- think I heard my first metallic tink from it just yesterday while taking a used car lot owner out for a simple test drive but otherwise no grinding or metallic actions are heard.  Just a consistent increases-with-speed whine with a hint of wobble to the whine.

The issue:  Topped off the rear diff fluid with 450ml out of the 1.2 capacity and have good reason to beleive that its been leaking for weeks. I can't say with any real accuracy how long the whining sound has been there but would guess a couple of weeks before it was really noticed.

Questions:  Is there any worthwhile status to be gained by taking off the cover and peering in there with a flashlight?  Moreover, without removing any other parts other than lowering the exhaust to allow for easier access to the diff cover, can I attempt to investigate the condition of the bearings and races?  I'm hoping that there won't be anything too metallic at the bottom of the housing.. and would then I be correct in assuming that the bearing(s) are breaking down and the diff can be saved??

I've been told by a mechanic that the pinion bearing doesn't like running with low oil the most of the bearings but have no way of gauging this opinion towards and how it fits with the sho. 

I'm watching the oil level by the week now and am definitely leaking the top up amount in 5 days or so.  I'd ideally like to sell the car with this issue slight fixed or not at all as it's a bad money proposition. 

Questions: With my severely rusted underbody can I have reasonable success trying to replace this leaking axle seal?   I'm assuming the carrier assembly needs to come out in order to remove the axle???  is that right?

As always, your support is greatly appreciated and I just wish I had more time and money to appreciate this great community. 

[Fozzforded]

found this section finally in Alldatadiy and would say that my hard sell has just got a lot harder

"....The pinion seal and the differential halfshaft seals are the only serviced components of the rear drive axle. There are no stub shaft bearings in the differential housing and the differential housing cover uses a silicone sealant rather than a gasket. If other components of the rear drive axle or the ATC are worn or damaged, a new axle assembly must be installed."

So what difficulty can one expect trying to replace a leaky rear axle seal?  ie the one on the driver side

Thanks

[SHOdded]

This is what the manual says about the seals:

Analysis of Leakage

Clean up the leaking area enough to identify the exact source.

A plugged Rear Drive Unit (RDU) housing vent can cause excessive pinion seal lip wear due to internal pressure buildup.

Verify the RDU lubricant level is even with the bottom of the fill hole.

Axle Vent

A plugged vent will cause excessive seal lip wear due to internal pressure buildup. If a leak occurs, check the vent. If the vent cannot be cleared, install a new vent.

Drive Pinion Seal

Leaks at the drive pinion seal originate from the following causes:

Damaged seal
Worn seal journal surface
Any damage to the seal bore (dings, dents, gouges or other imperfections) distorts the seal casing and allows leakage past the outer edge of the drive pinion seal.

The drive pinion seal can be torn, cut or gouged if it is not installed correctly. The spring that holds the drive pinion seal against the pinion flange may be knocked out and allow fluid to pass the lip.

Metal chips trapped at the sealing lip can cause oil leaks. These can cause a wear groove on the drive pinion flange and result in pinion seal wear.

When a seal leak occurs, install a new drive pinion seal and check the vent to make sure it is clean and free of foreign material.

A new drive pinion flange must be installed if any of these conditions exist.

Drive Pinion Nut

NOTICE: Install the drive pinion nut to the correct torque specifications or damage to the differential components may occur.

On some high-mileage vehicles, oil may leak through the threads of the drive pinion nut. This condition can be corrected by installing a new nut and applying threadlock and sealer on the threads and nut face.

Differential Seals

NOTICE: When installing shafts, do not allow splines to contact seals during installation or damage to the seals may occur.

Halfshaft pilot bearing housing seals are susceptible to the same types of damage as drive pinion seals if incorrectly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. The seal journal surface must be free of nicks, gouges and rough surface texture.

As far as replacing the stub shaft seals:

Removal

NOTE: The Rear Drive Unit (RDU) does not have stub shaft pilot bearings. It has stub shaft seals only.

Remove the halfshaft assembly. For additional information, refer to Section 205-05 .
Using the Torque Converter Fluid Seal Remover and Slide Hammer, remove the stub shaft seal.

Installation

NOTE: Lubricate the new stub shaft seal with grease.

Using the Front Axle Oil Seal Installer and Handle, install the stub shaft pilot bearing housing seal.

Install the halfshaft assembly. For additional information, refer to Section 205-05 .

[SHOdded]

The ATC is actually replaceable separate from the RDU assembly if you can find the part.  That's the trick LOL.  But IDK if there is an engineering reason for servicing only the entire RDU as an assembly, or it is a timesaving measure of some sort.

This is how the RDU is supposed to work:

Rear Drive Axle and Differential
The rear drive axle consists of the following components:

• Dished circular flange
• Full-time Active Torque Coupling (ATC)
• Aluminum housing with steel housing cover
• Matched ring and pinion
• Conventional open differential
• Rubber bushing isolated mounting points
• Cover-mounted axle vent

The rear axle drive pinion receives power from the engine through the transaxle, Power Transfer Unit (PTU), driveshaft and ATC , and is always engaged. The All-Wheel Drive (AWD) system on this vehicle is equipped with a bar-coded rear axle to reduce the tolerance of electrical current-to-torque delivered by the ATC . The 4X4 control module uses this bar code information to match the clutch characteristics of the ATC with the desired output torque. The pinion gear then rotates the differential ring gear, which is bolted to the differential case outer flange. Inside the differential case, 2 differential pinion gears are mounted on a differential pinion shaft, which is pinned to the differential case. These differential pinion gears are engaged with the differential side gears to which the halfshafts are splined. The halfshafts are held in the differential case by a driveshaft bearing retainer circlip that is located on the inboard CV joint stub shaft pilot bearing housing. When each halfshaft is installed, the driveshaft bearing retainer circlip engages a step in the differential side gear. As the differential case turns, it rotates the halfshafts and rear wheels. When it is necessary for one wheel and halfshaft to rotate faster than the other, the faster turning differential side gear causes the differential pinion gears to roll on the slower turning differential side gear. This allows differential action between the 2 halfshafts. The pinion seal and the differential halfshaft seals are the only serviced components of the rear drive axle. There are no stub shaft bearings in the differential housing and the differential housing cover uses a silicone sealant rather than a gasket. If other components of the rear drive axle or the ATC are worn or damaged, a new axle assembly must be installed.

[SHOdded]

And yes, the RDU is definitely in the beginning of the end stages.  If you can find the ATC, and IF you can confirm the gears etc are 100% healthy, then MAYBE you can replace just the ATC.  No stats to say yea/nay to this approach.

[jman]

The first thing I'd look is for a plugged breather (which is in line with the info posted by SHOdded). I'd assume the PTU has one as well.
I've solved oil leaks twice just by doing this, had an AWD Sienna that was leaking diff oil, removed the breather, cleaned it and the leak stopped http://www.siennachat.com/forum/21-sienna-care-maintenance/2152-differential-maintenance-awd-models.html
My Mazda 6 (manual transmission) was leaking transmission fluid thought the input shaft seal, fixed by simply removing the transmission's vent and cleaning it.

That could fix your leak, the whine, most likely a bad bearing.

[Fozzforded]

Many thanks SHOdded

so you think that the issue might be with the ATC at this point?...


Q:  Would you advise against letting a tranny shop poke around the interiors looking for the breaking part(s) and then trying to rebuild based on replaceable parts? 

The manual says that its not a serviceable assembly (rear diff); yet the last two mechanics I asked have said that tranny shops can rebuild/repair without replacement..


Q:  Will driving around with the diff humming ( likely cause any other component damage ie. ATC or driveshaft joint if I did drive it until complete diff failure? 

Obviously I am sidelining the car if/when I hear metallic grinding or such but at this point its seems as though I'm not doing any further damage other than waiting for the first audible red flags of either flying metal or the hum intesifying beyond my nerves ability to cope.

I am getting worried about collateral damage caused by the differential failure and then having a write-off on my hands....

[Fozzforded]

thanks jman.  I'm on my way to locate the vent now

[SHOdded]

Can't say for sure, could be the ATC at fault or a bearing/gear at fault ...

Shouldn't hurt the driveshaft driving around with the RDU whine.  Grinding etc, yeah def, put the SHO on the DL.

[jman]

thanks jman.  I'm on my way to locate the vent now

Hope that works... here is an interesting video I found that might help you https://www.youtube.com/watch?v=4oSb8LgV8iU
It appears that there is a hose attached to the vent so check that that hose is not plugged.

[Fozzforded]

Been pulling axles and grey hair trying to get this all sorted out and now have the good fortune of hard shifts into D and R from P.  Just when I was getting the hang of feeling good about the first real repair executed, this happens.

I did eventually manage to get a new seal into the differential and was pretty pleased that it went off with only 4 attempts of making seal seating tool which was easily corrected by going to the plumbing section at the local hardware store in the finale.  ABS, crazy carpet and bolts, in no particular order or function, were able to install the seal.  By the time the seal did go in, there was a lot of ATV gasket maker on the perimeter of the seal to amend early install attempts damage.  A quick 20-minute test and smile later, not a leak and disaster averted.  Not 2 hours of driving later does the hard shifting enter the fray.

Question:  With the new hard shift into D and R --but otherwise relatively familiar feeling shift quality while driving-- is the pinion bearing a possible fault for the hardness into these initial gears? 

Morning startups on the cold motor seem to really exacerbate this condition and when I initially start to roll forward the car lunges into about 10kms/hr right off the line.  I suspect reverse will behave similarily in this morning test but haven't tried.  This condition does lessen greatly as the motor warms but a hint of this remains even on a warm motor.   


Questions:
1. Should I be looking at trying to get the bearings all replaced in the differential if it is possible?
2. I am at the mercy of the tranny shop, but will an attempt to limit my exposure to excessive rebuild costs be limited by delivering the differential pulled from the car?   
3. What might be a good estimate of cost for replacing all the bearings only?
4. Can the bearings be installed with a common tool if I go buy a used unit and attempt to do this myself?
5. Knowing myself I should ask:  will doing nothing give me a better return on my investment at this point??  I think I see the pattern here so just ignore this last question please:)

All advice is great and appreciated. 

Cheers