Back in 2014 I started the following thread about leakage where the two rear axles enter the differential:
https://mitsubishiforum.com/forum/mi...al-leak-46066/
Both seals were eventually replaced under warranty.

Fast forward to today. The rear diff is leaking at the front, as shown in the following photos and diagrams.







I believe the seal that has to be replaced is number 29 on the last diagram.

To those members who have done this job, how difficult is it to replace that seal? How many hours would it take an experienced Mitsubishi technician to replace that seal?

Thanks very much for any advice.

 

For me it started to leak this winter on seal 9 (your last diag). In fact there are 2 such seals on left and right sides.

I've measured how much oil I actually lost and it turned out to be about 40-50mL which is about 10%. I added oil, cleaned up the whole differential and since few months there was no leak observed. My theory is that the vent (on top of the diff) was plugged with snow or ice during the winter (we had harsh winter this year with lots of snow) and then somehow the internal pressure got increased and oil was pushed through that seal No. 9. I turned on 4WD couple of times in february-march so maybe that caused pressure increase.

 

Thanks very much for the input.

Exactly where on the differential is the vent that you talk about? (As I said in my first post, one side seal was replaced in 2014 and the other a few years later. Neither of those is leaking at the present time, so I'm thinking that the front is just starting to fail, as the side seals did many years ago. But maybe that vent is in fact the culprit, so I will attempt to clear it.)

While I'm typing, after I started this thread, I emailed the closest Mit. dealership for a quote to replace the front seal. Today I received it-- $25 CAD for the seal and $1,352 for labor (of course this does not included 5% GST)! That must be roughly 8 hours labor at $150 per hour. What the heck does replacement of that seal entail -- removing the entire differential from the vehicle, disassembling it entirely and replacing the seal? After all, we're not talking about a rear main seal replacement for the engine!

The reason I'm reluctant to DIY is because of the position of intermediate support on the "propeller shaft" and the differential itself. I'd have to use a creeper and doing the job would be extremely uncomfortable for my 73-year-old back. Last year's timing belt + job just about killed me. I don't want to undertake a positionally more difficult job this year and end up at a real undertaker.

 

Here is a great video of the procedure to completely remove the diff from the vehicle, as well as replace ALL the seals:
The video maker's vehicle has the tailgate like ours, so the year of the vehicle must be close to ours.

I think the photo at the very beginning of the video is also useful.


Here's my tentative procedure to replace only the front-most seal.
1. After draining the diff, remove the four nuts that hold the coupling (blue arrow) to the diff.
2. Remove the bolts, etc from the intermediate support (red arrow) and lower the "propeller shaft" out of the way.
3. Disconnect the vacuum hose from the coupling housing and disconnect the electronic plug/socket.
4. Remove the four bolts that hold the coupling to the rest of the diff and slide the coupling off the rest of the diff.

(Here's where I'm fuzzy. Does the coupling just slide off the splined shaft poking out of the rest of the diff, or is there a bolt holding the splined shaft into the coupling? In the video, I cannot see threads inside the hole in the end of the splined shaft,

so I believe that the four bolts holding the coupling to the diff replace a single bolt screwed into the end of the splined shaft that might hold the coupling to the shaft. But if there is indeed a bolt, exactly how do you remove it if it's inside the coupling?)

5. Remove the old seal and replace it with a new seal. (Certainly easier said than done.)
6. Install/connect things in reverse order.

Here's a question that bother's me just a bit. If the diff. does not have to be removed from the vehicle in order replace the seal, and the seal can be replaced in the manner I described above, why is Mit. charging so much labor to replace the seal? For an experienced tech who's done this job a number of times, I can't see how this would take more than two, possibly three, hours.

 

I have just now found out that the coupling slides right off the splined shaft after removing the 4 bolts that secure it to the diff. and that it is not necessary to remove the diff from the vehicle to replace the front seal. My only concern is seating the new seal properly so that it does not leak after I get everything re-assembled.

(I know of a DIY repair place around here that charges $30 per hour for the use of a lift and tools. I may go there for the first time to do this job. This will also be the first time I've ever worked on a vehicle while it is on a proper lift.)

I guess the Mit dealer was attempting to "maximize profit" when making that quote. Maybe I'll buy the seal from them.

 

In short, I bought a seal from Mitsubishi, went to the DIY repair place and, 3.5 hours later, had replaced the pinion drive seal. Today, four days after completing the job, there has been no leak. Knock on wood.

Because of the leaking seal, the electronically-controlled coupling had a lot of oil inside it. The metal area around the leaking seal also had a great deal of oil covering the area. Removing the leaked oil from those two parts took me quite some time and a lot of brake-cleaning spray and paper towels. (There is no oil seal in the coupling. The leaked oil had somehow flowed through the internals of the coupling and leaked out of the front of the coupling, downward and then backward toward the rest of the diff. It is only the pinion seal that prevents oil from leaking into the coupling and, eventually, onto the floor.)

After those parts were reasonably clean, I removed the old seal using the larger of these two seal pullers (now on closeout sale at Princess Auto) that was handed to me by the DIY staff. The larger puller is surprisingly large, but this is actually a good thing because it provides good "swing room" for a hammer.


The hooked part of the puller is placed in behind the metal front lip of the seal and either of the two handles of the long puller is struck outward, toward the front of the vehicle, with a hammer. Because of my lack of experience with the tool, it took me about 4 or 5 hits with the hammer to remove the seal. Knowing what I know now, I'd have that seal out of there with one or two hits in just a few seconds.

Installing the new pre-lubricated seal is done by first positioning the seal in the opening as squarely as possible and lightly tapping around the seal using the universal tool - the hammer. After a few minutes of careful tapping, the seal was where it was supposed to be.

Semi-drying sealant is then applied to differential, and the coupling with large curved washer is then slid onto the splined shaft and pushed toward the diff until the two faces meet. The splined shaft guides the sealing surface of the coupling into the seal perfectly. Then the mounting bolts are screwed in; the rubber hose is re-attached to the fitting on top of the coupling; then the electrical connection is made by plugging the plug into the socket.

Then the propeller shaft is connected via four nuts to the coupling and the center bearing mounting is secured to the vehicle. The final steps are the securing of the propeller shaft protector and the filling of the differential with Mit. LSD hypoid gear oil SAE 80.

If I had to do this job again tomorrow, with my recent experience, I believe I could accomplish the same task in about two hours.

BTW, the nut shown in the previously posted diagram is screwed onto the outside of the splined shaft, securing the shaft against a bearing inside the differential.

Again BTW, being able to work on the front-to-rear center-line of the bottom of the vehicle while standing under a proper lift was an absolute joy compared to sliding or using a creeper on my back. Luckily, most normal maintenance can be done from the outer periphery of the vehicle with the vehicle just jacked up as high as possible and "reaching in" from a seated position or lying just barely under the vehicle as when changing oil and filter. This is the first time in my life that I've really needed to be working under a lift and, luckily, that DIY place was available. All DIYrs should have access to similar places in their area so that dealerships can't take them to the cleaner.

 

Something I forgot to mention.

When I disconnected the rear propeller shaft from the electronic coupling, I marked the shaft and the coupling so that I could install the shaft as it was originally installed. Unfortunately, I used chaulk to mark rather than, say, paint or a scored mark into the steel. Well, by the time I had done all the manipulating of the coupling, the chaulk mark on it had disappeared. So when I re-attached the propeller shaft to the coupling I could not be sure that the two parts were joined exactly as they were when I disassembled them. The vehicle runs perfectly, as far as I can tell, and there are no trouble codes being generated by the ECU, again, so far. But I have a couple of questions for the forum.

What is the purpose of making certain that these two parts are assembled exactly as they were disassembled?

Is there any way to now determinne the "correct" orientation of the four holes of rear propeller shaft on the four studs of the coupling?

Thanks.

 

Further to my last post about being certain that the holes in the yoke match the studs on the coupling, here is what the service manual says about making marks.



Mitsubishi uses the term "phase alignment". Does anyone know exactly what "phase alignment" means? Is it a physical phase alignment that probably relates to some sort of balancing (like, say, a wheel balancing), or is it an electronic/magnetic phase alignment?

Thanks.

 

I reality the driveshaft is balanced independently so its not going to make any meaningful difference which way it is installed to the diff. Phase alignment of driveshafts is normally referring to the alignment of the universal joints (at each end of the driveshaft) relative to each other. If they are out of phase it will result in driveline vibrations - but that can only happen if a slip joint is pulled apart and the two halves are not aligned correctly.

 

Thanks for the input, shane. I also thought that driveshafts are balanced independently and then installed into the vehicle.

What you say about phase alignment of the universal joints makes perfect sense if the propeller shafts are going to be, say, re-built with new parts, and things might get put together with the joints not oriented exactly as they were originally, but why would Mit. specifically state to put mating marks on the electronic coupling and rear propeller shaft yoke, presumably, so that when the yoke and coupling are re-attached, the studs of the coupling go through the exact same holes in the yoke? Unless there is some balancing or electromagnetic reason for this, it makes no logical sense. It would be like saying that, after removal, the end of the front propeller shaft has to be inserted into the transaxle in the exact same spline as it was when it was removed. That would also make no sense.

Maybe Mit. states this simply because it makes good sense to put things back together exactly the way they were before disassembly.

I just wish that Mit. would tell the reader exactly WHY the yoke and coupling should be joined exactly as they were before disassembly, rather than have users of the service manual resort to speculation. (There may in fact be another location in the pdf service manual that explains what this phase alignment is in more detail, but the manual is so huge that I have not yet been able to find it.)

Again, our vehicle continues to run perfectly with no trouble codes, so maybe, just by pure luck, I re-assembled those parts exactly as they were before disassembly. (AFAIK, I did not rotate the inner workings of the coupling as I cleaned them, and, after replacing the pinion seal, I rotationally aligned the coupling with the pinion so that when I first slid the coupling onto the splines of the pinion, I did not have to rotate the coupling at all to align the bolt holes on the coupling with the threaded holes in the diff. If I did, it would have been only a small fraction of 90 degrees. If I remember correctly, after bolting the coupling to the rest of the diff, when I raised the propeller shaft to place its yoke back on the coupling's threaded studs, the holes in the yoke were pretty much already aligned with the studs on the coupling.)

Thanks again.