2009 Yukon Rear Main Seal Failure

[Sagmanovich183]

Hey everyone! About 60k miles since I posted about my Vigor shocks, lost my dog (koda had cancer) and sierra denali (230k miles - frame cancer etc) in the photo and I have a question about my leaking main seal in my '09 Yukon. Only has 140k on it.

I just changed oil cooler thermostatic valve and line set and no go. No leak in oil sender, oil filter or pan gasket either.

After a light pressure wash oil is coming out at plastic dust covers adjacent starter and oil filter and down and out the bottom of bell housing. Seems it's being flung off at main seal but what do I know.

I'm more than handy mechanically but given a recent rebuild of my own (3 shoulder & arm tendons) I'll be assisting my long term friend in his shop. 'As useful as a one armed paper hanger' as my dad would say.

Questions
I just wanna avoid any pitfalls.

If rear main is felpro ok vs OEM, other issues anyone can share insight on?

A lot of extra work but should we do pan gasket, oil pickup O-ring, other?

Edit: 8/29 Labor day weekend.

Progress: I dropped the oil pan, pressure washed it, highTacked a FelPro gasket to it, carefully applied ultra-Black RTV to the four corner seams ( at front and rear plate parting lines) after carefully cleaning those. I hand tightened, waited an hour and torqued per spec...waited 24 hours. Reassembled differential and all that and I just drove about 15 mikes out and back so 30 miles total. 45-50 mph.

Clearly there is a constant drip, clearly making its way down the starter side of the motor and dripping off to the passenger side of the bell housing observation port... which looked dry inside before and looks dry now. (I did not dye check)

From reading just a couple (I will read all now) with my hands covered in oil from wiping down the oil pan/bell housing seam I'd have liked to post my success but I'm still leaking, slightly more than before I'd say.

*****... i feel I need to start the truck, and really dial in on the passenger side (where I know comments suggest a cam/crank position sensor being the next point (other than main seal of course) up the ladder. I will likely pull the fender skirt, tire and maybe even starter ( start the truck and disconnect while running - idk) I have an observation mirror and have seen no oil from OP sender, valve cover or valley pan but I'll exhaust those for sure before attacking a main seal... $1,200 not including incidentals is what a local tranny shop I trust quoted. I can't do it on blocks...

the beat goes on here... again I'll respond to all here and continue the brainstorming as it is appreciated

Friends call me Sags...

 

[Sagmanovich183]

found this very helpful thread and I'm reading through it now.

Thread 'Rear Main'
https://www.tahoeyukonforum.com/threads/rear-main.154627/

 

[rdezs]

The while you're in their list, often does include the oil pickup tube o-ring. It's actually more of a maintenance item. You also want to replace the barbell that's accessible once you remove the rear cover. For the rear main seal itself, I always use the felpro. Only thing to remember is it goes on dry. No oil film on the crankshaft or on the seal itself. Wipe down with brake cleaner prior to install.

Before committing to the rear main seal, check the back side of the engine valley cover/VLOM plate. There well-known after 100,000 miles to have a few of the bolts loose. That will cause a leak down the back side of the engine and mimic rear main seal. After shutting off the engine you can reach back there with your hand, feel around just below the gasket line for the valley cover. If you pull your fingers up and it's oily, you have your answer. (Or the oil pressure sending unit itself, which is on the back side of the cover)

It's also worth confirming your valve cover gaskets aren't leaking, prior to diving in on the rear main.

Also, above the starter is your crankshaft position sensor. The o-rings on the sensor can also leak, and then you have the dipstick tube itself. Heard of a few in high salt areas rust through... Also sending oil back by the starter and bell housing. You pretty much have to pull the starter to check out those two items.

 

[Foggy]

My thought was the crank sensor too when mentioned leak is by starter !!
Check that first !!

 

[West 1]

If you do determine it is a main seal leak the seal is mounted in an aluminum plate. The plate seals to the block with a gasket. The leak can be at the plate as well as the seal. In my case every leaking rear main I have fixed it was actually the plate gasket leaking. Dorman makes a replacement plate with the new seal installed. I have also used the Fel Pro rear main seal with no leaks. Read up on proper install of a teflon rear main seal. Instructions are different from any seal you have ever used. Teflon is unique, goes in clean and dry, no oil, no grease no lube. The Seal and crankshaft must be clean and dry on install to seat properly.

 

[j91z28d1]

every ls oil pan gasket seems to leak around this time too. Definitely do that while yours in there for the rear main/plate.

if you have the 6 speed tranny a new torque converter is worth doing too.

 

[lspann3525]

make sure to use alignment tool on the rear cover. some alignment tools require you to mount the rear cover without the seal in place, insert the alignment tool then torque rear cover then install rear seal

 

[Sagmanovich183]

The while you're in their list, often does include the oil pickup tube o-ring. It's actually more of a maintenance item. You also want to replace the barbell that's accessible once you remove the rear cover. For the rear main seal itself, I always use the felpro. Only thing to remember is it goes on dry. No oil film on the crankshaft or on the seal itself. Wipe down with brake cleaner prior to install.

Before committing to the rear main seal, check the back side of the engine valley cover/VLOM plate. There well-known after 100,000 miles to have a few of the bolts loose. That will cause a leak down the back side of the engine and mimic rear main seal. After shutting off the engine you can reach back there with your hand, feel around just below the gasket line for the valley cover. If you pull your fingers up and it's oily, you have your answer. (Or the oil pressure sending unit itself, which is on the back side of the cover)

It's also worth confirming your valve cover gaskets aren't leaking, prior to diving in on the rear main.

Also, above the starter is your crankshaft position sensor. The o-rings on the sensor can also leak, and then you have the dipstick tube itself. Heard of a few in high salt areas rust through... Also sending oil back by the starter and bell housing. You pretty much have to pull the starter to check out those

The while you're in their list, often does include the oil pickup tube o-ring. It's actually more of a maintenance item. You also want to replace the barbell that's accessible once you remove the rear cover. For the rear main seal itself, I always use the felpro. Only thing to remember is it goes on dry. No oil film on the crankshaft or on the seal itself. Wipe down with brake cleaner prior to install.

Before committing to the rear main seal, check the back side of the engine valley cover/VLOM plate. There well-known after 100,000 miles to have a few of the bolts loose. That will cause a leak down the back side of the engine and mimic rear main seal. After shutting off the engine you can reach back there with your hand, feel around just below the gasket line for the valley cover. If you pull your fingers up and it's oily, you have your answer. (Or the oil pressure sending unit itself, which is on the back side of the cover)

It's also worth confirming your valve cover gaskets aren't leaking, prior to diving in on the rear main.

Also, above the starter is your crankshaft position sensor. The o-rings on the sensor can also leak, and then you have the dipstick tube itself. Heard of a few in high salt areas rust through... Also sending oil back by the starter and bell housing. You pretty much have to pull the starter to check out those two items.

I hit the oil pickup o-ring. My pan was super clean... I'm on top of the oil changes. I need to tackle this position sensor in the AM but tbh I feel like i made it worse changing the oil pan - as careful as I was. But that oil was present at the starter for sure before the pan change. I will post photos of the pan gasket.. it looked to have a clear failure just tranny side of the supply/return porting. I ran an medium tech machine shop for decade... i woulda fly cut/redressed the pan if I was still there... I just can't see that being the problem though.. a good lock at passenger side is next up

 

[Sagmanovich183]

make sure to use alignment tool on the rear cover. some alignment tools require you to mount the rear cover without the seal in place, insert the alignment tool then torque rear cover then install rear seal

Hey, Ispan!, thanks, I am hoping we find something on the passenger side and don't have to go to main seal. I'm ripping into all the low hanging fruit that has been mentioned before the RMS!!!

 

[Sagmanovich183]

every ls oil pan gasket seems to leak around this time too. Definitely do that while yours in there for the rear main/plate.

if you have the 6 speed tranny a new torque converter is worth doing too.

Hey J, thanks, I am kinda boiler playing sim rents ( torque converter replace .. with 6L90 i here is a possibility) hoping we find something on the passenger side and don't have to go to main seal. I'm ripping into all the low hanging fruit that has been mentioned before the RMS!!!

 

[Sagmanovich183]

If you do determine it is a main seal leak the seal is mounted in an aluminum plate. The plate seals to the block with a gasket. The leak can be at the plate as well as the seal. In my case every leaking rear main I have fixed it was actually the plate gasket leaking. Dorman makes a replacement plate with the new seal installed. I have also used the Fel Pro rear main seal with no leaks. Read up on proper install of a teflon rear main seal. Instructions are different from any seal you have ever used. Teflon is unique, goes in clean and dry, no oil, no grease no lube. The Seal and crankshaft must be clean and dry on install to seat properly.

If you do determine it is a main seal leak the seal is mounted in an aluminum plate. The plate seals to the block with a gasket. The leak can be at the plate as well as the seal. In my case every leaking rear main I have fixed it was actually the plate gasket leaking. Dorman makes a replacement plate with the new seal installed. I have also used the Fel Pro rear main seal with no leaks. Read up on proper install of a teflon rear main seal. Instructions are different from any seal you have ever used. Teflon is unique, goes in clean and dry, no oil, no grease no lube. The Seal and crankshaft must be clean and dry on install to seat properly.

Hey West, thanks, I am boiler plating a kinda common response after my post edit for progress and first response I made with a few other details I added. I am in the driver seat once ago up on ramps texting this on my Iphone with hands once again covered in oil. I am hoping we find something on the passenger side and don't have to go to main seal.. I have seen the teflon main mentioned as well as porous ORM plates and it seams fel-pro is trusted for RamS.I'm ripping into all the low hanging fruit that has been mentioned before the RMS!!! Like I've said the leak is slightly worse and clearly on passenger side so I'm all over that tomorrow.

 

[Sagmanovich183]

My thought was the crank sensor too when mentioned leak is by starter !!
Check that first !!

Hey Foggy, fitting handle as that is what my rear window looks like with oil misting on it. I am just tryiin' to saying hi and thanks to all who've reached out. Like I've note we are hoping we find something on the passenger side and don't have to go to main seal. I'm ripping into all the low hanging fruit that has been mentioned before the RMS!!!

 

[Sagmanovich183]

found this very helpful thread and I'm reading through it now.

Thread 'Rear Main'
https://www.tahoeyukonforum.com/threads/rear-main.154627/

I had high hopes that the leak was a pan leak after seeing what looks like a gasket failure around the oil cooler/thermo-bypass and relatively pristine surfaces around the rest of pan (and no viable oil forward of the oil cooler lines or starter) There was oil on both sides at oil cooler lines and starter before the pan gasket change.

I will be into all that has been suggested in the AM... been on my back with one good and one not so good arm for days now ... so much for a trip south this weekend

Sags

 

[West 1]

I did not go back to the very first posts but if your leak is bad as you mention a couple things to rule out. The oil pressure sender up top on the back of the manifold, check it for leaks, also check the valley manifold under the intake manifold. They can leak at the rear and cause issues.

Mine leaked on the pass side rear by the starter, it was not the RMS but the plate gasket that holds the RMS. If you are careful and install the plate with the new seal in it seal surface protected by the plastic install tool that comes with it you can install this seal without an alignment tool. As it is installed the seal will self center, no bolts yet installed. At this point your job is to carefully insert the bolts and NOT pull it off center. Lightly bring the plate bolts down just till they are about to touch. Then slowly tighten them up to the block maybe 1 or two turns at a time jumping around the plate to bring it tight evenly and slowly. at this point leave the oil pan long bolts threaded in but very loose, you want them in place so your oil pan gasket stays put but if you tighten them early you will distort the RMS causing leaks., don't tighten them till you have the plate firmly in place and torqued.

With the pan off be sure to replace the Oil Pump O ring, be careful as there are differing size rings for this. Melling has a good instruction sheet telling you which to use based on your pick up tube shape.
Replace the oil pressure by pass valve in the oil pan right next to your oil cooler lines. If that goes bad you loose oil pressure.

Your old pan gasket shows some oil leak staining but most on the driver side with a little on the pass side so not sure if this is your large leak you are chasing.

Hope the pan gasket fixes your leaks, fingers crossed.

 

[rdezs]

The last rear main seal I did only left droplets on the two starter bolts, and the plastic inspection cover between the starter and the flywheel. Looking up through the bell housing inspection hole it was dry.