Sudden gear oil leak from bell housing 2008 4 cyl manual trans 4x4

My transmission has never leaked or even seeped before. Suddenly about a week ago I noticed a spot in my driveway. A friend had just parked there so I figured it was his. Fast forward to today and I look under my truck and it's leaking, and bad! Like, a 2 inch puddle after being parked for 5 minutes! Stops leaking when I stop driving.

Upon inspection I determined it's gear oil and it's coming from where the bell housing meets the engine. All over the bottom of the little inspection door and dirty gear oil puddle on the bottom of the bell.

What would cause such a bad leak out of nowhere? Do transmission seals fail catastrophically? Input shaft seal I assume. Is there anything else in the vicinity that could be leaking? Once I drop the transmission is it an easy fix or no?

 

Sure it isn't the rear main seal? Just a rarity for the trans to leak there.

 

No, I'm not sure, and I'm starting to convince myself you're right.

I was going by smell. It smelled faintly like gear oil and the MT90 in my transmission isn't super stinky to begin with. But I'm also due for an engine oil change so my oil is old and it was dirty from leaking through the bellhousing picking up dust. At this point I'm not sure if it's gear or engine oil and am going to have to spend some more time under there assessing.

 

Did you pull the plastic inspection cover from the bottom of the transmission to see if you can look at the seal?

 

Yep. It's the rear main and if he took a picture of the undercarriage (namely the transmission and engine oil pan area) I'll bet you it is caked in old oil and new oil.

This is why it pays to inspect your undercarriage and just your vehicle overall during every service.

 

Thanks everybody for the comments and subtle implications. My vehicle is well maintained, last inspected undercarriage about 2 months/5,000 miles ago when I did my last oil change and it was dry and clean as it always has been. I inspected my rear main seal 2 years ago when I did a clutch job and opted not to touch it since it was fine. Whatever happened, happened suddenly and recently. I just took a sample from my engine, transmission, and mystery fluid dripping out of my bellhousing. See picture. I do not believe I have a rear main seal problem and I think after seeing the picture you'll agree. I am tracing brake lines and clutch fluid lines and haven't found anything out of the ordinary yet but I will continue to search into the evening. Of course it has to be coming from somewhere but for now I'm perplexed.

 

Looks strikingly similar to the left plate.

 

In person it's much more "green" in color if you look at the actual fluid between the dust particles. The smells are drastically different too.... left plate smells like gear oil. Middle.... well doesn't really smell like much of anything after whiffing that gear oil.

I think brake/clutch fluid is somehow getting in there. Can't figure how yet

 

Take a sample of that and get it into a water bottle of sorts, after that get some water in there and see if it dilutes, brake fluid is water soluble so if it ceases to exist in there after you fill it with water then there is your answer. If it does not and separates from the water than the issue is actually indeed an oil issue.

Transmission fluid destroys nitrile rubber gloves very quickly. I go through at least 2-3 pairs when working on anything transmission internal related at work just to give you an idea of the amount of damage it does them in that quick of order. If it is ATF, get a black nitrile style rubber glove and get some of that oil on it. If the glove starts getting all pruny looking, then it is ATF.

That would help rule out two of your potentials there if it is leaking as much as you indicated on your first post.

 

How does the reservoir look? Low?

The clutch slave leaking perhaps and dripping in?

 

I ruled out brake/clutch fluid. I took a sample from the brake reservoir and compared its miscibility in water with the mystery fluid and they don't match. Mystery fluid doesn't mix with water at all. So in summary, the mystery fluid, when compared to:

1. Engine oil has the wrong viscosity, color, and smell. Unlikely match.
2. Brake fluid has the wrong miscibility, impossible match.
3. Gear oil from the transmission has the correct viscosity, miscibility with water, almost the correct color, but the smell doesn't match. Most likely match I would say. Not sure why it doesn't stink, maybe the clutch dust neutralizes the smell somehow.

Really gear oil is the only thing this crap could be. Which bring me full circle back to the original question. Does anybody have any ideas what could have caused this seal to pop out of nowhere with seemingly no triggering factor? I cannot find ANY record of the 5 speed manual transmission mated to the 2TR having this type of problem anywhere on TW or anywhere else on the internet.

I'm prepared to drop the transmission but I don't know if this seal is something I can/should do with regular tools or if I need to get the transmission looked at by a transmission shop since this seems like such a rare failure.

 

If the 5 speed has a bolt on cover, around the input shaft, it could be leaking from there.

R155 transmission. It may just need a fresh application of silicone.