Rear Main Oil Seal

[Larryjb]

I'm actually beginning to doubt whether the rear main seal is leaking. However, the housing plate has a seal that may be leaking as well. I will move to do the oil pan gasket in the coming days.

The first picture is a general overview of the area:

There is a thin stream of oil on the back of the engine behind the flex plate, but it is hard to see with the camera. Even by eye it can be hard to see because the oil is very clean there, but it is there.

The second picture shows a huge magnification of the area in the hole of the flex plate. You can just make out the bottom of the rear main seal there. I believe I see a little wetness on the seal, but I suspect there is more oil sitting on the oil pan gasket at the back. However, I don't see a lot draining down from there. It is entirely possible the oil is following the lip of the oil pan over the the right and left sides where it drips.

The quality of the second image is not so great because of the magnification factor. The orange streak may about 1/3 up from the bottom of the image is, I believe, oil. The rear main is barely visible in the top 1/3 of the image. I do believe I see a little oil there.

So, there is the possibility that the oil I see on the lip of the pan gasket in the 2nd image is coming from the rear main. However, the drips on the road are getting more significant and will leave a 6" round patch of oil by the end of the day.

 

[Rocket Man]

I'm actually beginning to doubt whether the rear main seal is leaking. However, the housing plate has a seal that may be leaking as well. I will move to do the oil pan gasket in the coming days.

The first picture is a general overview of the area:
View attachment 242704

There is a thin stream of oil on the back of the engine behind the flex plate, but it is hard to see with the camera. Even by eye it can be hard to see because the oil is very clean there, but it is there.

The second picture shows a huge magnification of the area in the hole of the flex plate. You can just make out the bottom of the rear main seal there. I believe I see a little wetness on the seal, but I suspect there is more oil sitting on the oil pan gasket at the back. However, I don't see a lot draining down from there. It is entirely possible the oil is following the lip of the oil pan over the the right and left sides where it drips.
View attachment 242705

The quality of the second image is not so great because of the magnification factor. The orange streak may about 1/3 up from the bottom of the image is, I believe, oil. The rear main is barely visible in the top 1/3 of the image. I do believe I see a little oil there.

So, there is the possibility that the oil I see on the lip of the pan gasket in the 2nd image is coming from the rear main. However, the drips on the road are getting more significant and will leave a 6" round patch of oil by the end of the day.

If the leak is getting worse considerably fast that’s usually a main seal but not always. It’s just that it’s a seal with a moving part going through it so once it starts to go the moving part makes it fail faster than if it’s a seal on a non moving part like an oil pan or rear housing if that makes sense. I hope it’s not but I have a feeling. It’s still worth trying the oil pan gasket first imo.

 

[Larryjb]

I fully agree!

 

[wildcatgoal]

Benefit of dropping the T-case is you can open it up and install one of those oil pump spacer things so you don't end up with holes in your case. Takes 30-minutes.

You don't need to DROP the transmission, just pull it back enough to get to the rear main seal area. When you're done, slide it on back on and bolt it up!

If you're going to drain transmission fluid from everywhere it can possibly be while you're doing this, don't. Just sign yourself up to do a transmission flush after the job if you want to go to that level of fluid replacement instead of awkwardly trying to drain fluid from places that don't have a drain plug. Don't add work that isn't going to get your rear main seal job done.

Also great time to do the oil pan gasket (especially on a 2WD truck) and especially great time to replace the oil pressure sending unit and camshaft position sensor. Use AC Delco parts because those buggers are not easy to get to otherwise and you might as well avoid that .

The job took me most of a day because I took my sweet as time and kept loosing extensions despite (this time...) trying to place tools in a specific spot when I'm done. Nope, I proceed to act as normal dropping tools wherever and having to go look for what I needed later. I would starve as a line mechanic... tell you what. But the job is done, she doesn't leak anymore, and I didn't have to pay someone $800+ to do it for me (and shops around here really love them some Dorman parts and I do not like Dorman).

 

[Larryjb]

Thanks Nick,

I wasn't planning to actually "drop" the transmission, but dropping for me would be pretty much 30 seconds of dropping on the transmission jack. I do plan to disconnect everything because I don't want anything to get hung up or kinked. As for draining fluid, I plan to drain the torque converter so I can replace the transmission oil seal, drain the pan, and some fluid will likely come out from the lines as I disconnect the transmission cooler lines. I already replaced the oil pressure sender 2 years ago, but I don't think I touched the cam shaft sensor. I may need to pick one of those up.

However, I now suspect my main leaks are from the oil pan gasket, so I will limit my repair to the oil pan first. Unfortunately, I've got 4wd which means at least lowering the front diff. If the rear main is leaking, I'm not wasting any time or effort to have to dig into it again as most items required to remove the engine oil pan do not need removal for the transmission. In fact, the engine oil pan, even 4x4, should be a breeze comparatively.

I find this hard to believe you did this in a day, taking your time. That seems to be the norm, to pull the transmission, drop the engine oil pan, etc. But then, if you have 2wd you don't have the front drive shaft and diff to worry about, making the engine oil pan a breeze.

 

[Larryjb]

Ah, I've decided to completely rethink this. I've found a cheaper solution:
http://www.britishcarforum.com/bcf/showthread.php?80725-Leaky-rear-main-seal-leak-fix-for-1

 

[OR VietVet]

Thanks Nick,

I wasn't planning to actually "drop" the transmission, but dropping for me would be pretty much 30 seconds of dropping on the transmission jack. I do plan to disconnect everything because I don't want anything to get hung up or kinked. As for draining fluid, I plan to drain the torque converter so I can replace the transmission oil seal, drain the pan, and some fluid will likely come out from the lines as I disconnect the transmission cooler lines. I already replaced the oil pressure sender 2 years ago, but I don't think I touched the cam shaft sensor. I may need to pick one of those up.

However, I now suspect my main leaks are from the oil pan gasket, so I will limit my repair to the oil pan first. Unfortunately, I've got 4wd which means at least lowering the front diff. If the rear main is leaking, I'm not wasting any time or effort to have to dig into it again as most items required to remove the engine oil pan do not need removal for the transmission. In fact, the engine oil pan, even 4x4, should be a breeze comparatively.

I find this hard to believe you did this in a day, taking your time. That seems to be the norm, to pull the transmission, drop the engine oil pan, etc. But then, if you have 2wd you don't have the front drive shaft and diff to worry about, making the engine oil pan a breeze.

A mechanically inclined friend that works for beers and pizza makes the job easier and quicker but as the day wears on and the empty beer count climbs, you make up for the early speed at the end. Giggles all around. Plus, count your fingers at the end.

 

[OR VietVet]

Ah, I've decided to completely rethink this. I've found a cheaper solution:
http://www.britishcarforum.com/bcf/showthread.php?80725-Leaky-rear-main-seal-leak-fix-for-1

Yea, I can see how this would work.

 

[latvius]

If you have a remote oil cooler let me know as I have some tricks I learned the hard way on my Denali when you drop the front axle.

 

[Larryjb]

If you have a remote oil cooler let me know as I have some tricks I learned the hard way on my Denali when you drop the front axle.

I don't have an oil cooler in any way. Is it worth it to install? I believe all I'd need is the adapter, gasket, and hoses as long as I have the two plugs in the radiator.

 

[latvius]

Good question, I don't have an answer for ya.

 

[Larryjb]

I was planning to go ahead and do the rear main seal anyway since I have the time. The I looked at the prices of Dexron VI up here in Canada:

1 qt ACDelco 10-9243 Dexron VI is $29.00 Cdn. That would be $20 USD currently.
RockAuto has it for $4.11 USD, but won't ship fluids to Canada.

I'll still go ahead with the the oil pan seal.

 

[Larryjb]

As I prepare to do the oil pan gasket, I now am wondering what sealant I should use for the corners?

 

[latvius]

Permatex 85080 Ultra Black Maximum Oil Resistance RTV Silicone Gasket Maker, 9.5 oz. PowerBead Can

https://www.amazon.com/gp/product/B000HBGI1M/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[Larryjb]

I started the oil pan gasket job. Everyone seems to avoid dropping the front diff entirely. It seems that all you need to do is remove an electrical connector, vent hose, and the bolts securing the diff to the axles in addition to the mounting bolts for the diff. That can't be that hard to do when compared to the mounting bolts for the diff. At least one of those looks nasty to get at.

So I plan to drop the diff to give me more room.

 

[Larryjb]

Here's what I've done so far:

1. Support vehicle on 4 jack stands.
2. Remove both front wheels (22 mm works well, actually fits better than the imperial).
3. Remove skid plate (18 mm)
4. Drain oil
5. Remove cross member (2 short, 2 long bolts) (forgot to note size, probably 18 mm)
6. Drain front differential fluid (yellow colour, quite clean! ) (13 mm drain bolt, 15 mm fill bolt)
7. Mark axle/differential flange with chalk.
8. Mark front drive shaft.
9. These next eight steps did not have to be done, but I did them planning to remove the front differential entirely:
10. Remove transfer case splash shield (possibly unnecessary)
11. Place transmission in drive and release parking brake (possibly unnecessary)
12. Rotate front drive shaft to remove boot clamp. (possibly unnecessary)
13. Set parking brake. (possibly unnecessary)
14. Remove 2 drive shaft bolts (11 mm) (possibly unnecessary)
15. Release parking brake, rotate drive shaft 180°, reset parking brake (possibly unnecessary)
16. Remove last two drive shaft bolts. (possibly unnecessary)
17. Remove drive shaft from front differential, support with bungee cord. (possibly unnecessary)
18. Return transmission to Park.
19. Remove electrical connector to front differential.
20. Open electrical wire loom clamp on top of differential to release wire.
21. Remove vent hose.
22. Remove 6 15 mm passenger side axle-differential bolts.
23. Turn steering wheel to far left.
24. Remove 6 15 mm drivers side axle-differential bolts.
25. Support axles with bungee cord to protect CV joints.
26. Loosen all differential bolts but do not remove (21 mm)
27. Support differential with transmission jack.
28. Remove the two long bolts from differential mount.
29. Remove the two short bolts supporting differential from frame.
30. Separate idler arm to center link bolt. This allows center link to rotate away from differential as you lower it. NOTE 1: Every video I've seen, people are disconnecting the tie rod end to do this. They are taking off too much here. NOTE 2: I have not actually done this yet. After lowering the differential, it is nicely resting on the center link. This is now lowered enough that I should have no trouble removing the oil pan. If I do, it is a matter of one bolt on the steering linkage, then the entire differential will come out.

That's where it stands for now. This actually took me 4 hours to do. Yes, I work really slowly, but part of it was figuring things out, part of it was documenting what I was doing, and part of it was working inefficiently. At first I jacked up only the front wheels, but I realized that to separate the front drive shaft I'd have to raise the rear as well so that the drive shaft would rotate.

Here are some things that may be completely unnecessary and a complete waste of time:

Raising the rear of the truck.
Releasing the boot clamp on the front drive shaft.
Separating the front drive shaft from the differential.

If I decide to remove the front differential, then yes, doing those three things would be necessary.

I'll come back to edit this later as I continue with the oil pan removal.

 

[latvius]

Raising the rear of the truck gives you more room underneath
boot clamp no, just extra work
Yes you have to disconnect front drive shaft so axle drops easy
I never removed/disconected anything steering related on either my 4wd tahoe or awd denali

Also you dont need to rotate the driveshaft, undo the u clamps and pry it back it is designed to move back and forth (extend and retract)

 

[Larryjb]

...
I never removed/disconected anything steering related on either my 4wd tahoe or awd denali

Also you dont need to rotate the driveshaft, undo the u clamps and pry it back it is designed to move back and forth (extend and retract)

Separating the center link from the pitman arm is only if I were to actually remove the differential. Did you remove the differential without disconnecting anything steering related?

 

[Rocket Man]

Why did you drain the front diff and unbolt the axles? It will drop down far enough without doing that. All I did with it was remove the drive shaft and unbolt it from the frame. When I pulled the pan I pried down on it a bit.

 

[Larryjb]

Even for me, it takes 10 minutes to unbolt the axles. This way you get more room without having to pry, allowing you to use two hands to manipulate the oil pan. Also, I saw the videos of people trying to pry the axle down. I've heard you have to be really careful with the CV joints so I didn't want to take any chances messing those up. Thirdly, unbolting the axles allows the differential to drop down lower, giving you more room to fit the pan in.

Obviously, you don't have to do this. For me, 10 minutes of extra work will probably protect the neighbourhood from learning some new words.

I drained the front differential because that one is super easy and I've never done it yet. The rear diff is messier, and requires that you clean more gasket surfaces. I may run out of time before I can get to changing the rear diff this time. I also have to save time to change my parking brake shoes.