Need Help With Tranny Leak Location

Chasing a leak on a "new to me" 2010 SCLB 4WD Auto. Definitely tranny fluid. Definitely not the pan seal. The leak shows up primarily on the U-Joint of the front drive shaft at the front diff and gets slung around from there. The attached pic is looking straight up from the front of the front drive shaft. Note the fluid hanging from the connectors etc. I understand there is a vent up there and know where it is. Super tight in there, is there any way to access a view? Is there anything else up there that can leak? If it is the vent, why would it be leaking? Tranny fill/filter are correct via full fluid change temp/fill procedures etc. Thanks for any ideas.

 

There are fluid line(s) that go to the radiator. Are they leaking?

 

I'm familiar with the lines coming from the bottom, front, passenger side of the tranny that feed the trans cooler. Those are not leaking. Are there others? I'm thinking not? I am 99% sure it is coming from the vent as the bracket at the end of the vent line is freshly wetted. But why.....? Going to hook up an OBD temp monitor to look at at pan and TC temps next.

 

Calling in the big gun @gearcruncher

Any thoughts?

 

Very unusual to see a vent leak on the A750 series transmission . I beleive this is one of the first complaints I have seen at Tacoma World dealing with a leaking vent .
Overheating is the number 1 cause for a trans vent to leak . I would throw a temp gauge at it and see what kind of numbers you are getting .
Aftermarket cooler ? what condition is your radiator in ? If the engine overheats , the transmission also overheats
Next is foaming fluid . Are you positive the trans service was done correctly ?
What transmission fluid was used ?
Mileage ?
In a very worst case scenario I have seen valve bodies get so hot , they warp and you get a leak out the vent but I have never seen any of these types of issues with the A750 series .
More info here
https://www.transmissiondigest.com/vacuum-testing-a750e-f/

 

Thanks for checking in Gearcruncher. I'm with you, seems very odd.

Cooler is stock and seemed to be flowing just fine during the fluid exchange.
Valvoline fluid per your recommendation.
120K on the truck. No engine heating problems that I am aware of, but will be getting OBD temp data for the trans, T/C and engine next week.
I'm sure I performed the fluid exchange correctly. Not rocket science, not the first time I've done it (I own another 2010 as well). Your directions are very good.

I am going to re-clean the world, bag the end of the vent to make damn sure I'm not just looking at fluid slung upward from the front to the front drive line, get temp readings. Will check back in when I get some results.

 

I assume you found the vent?
It’s not easy to see or get to.

If it’s the vent, you’ll know once you “see it”.

I took me a good 15mins of searching to actually find it.
https://www.tacomaworld.com/threads/can-a-clogged-breather-cause-the-front-diff-to-leak.761349/#post-27147395

 

Well... I'm thinking this is the vent on mine (not actually mine, pic from another thread). Looks a bit different than what is in your link. Top back of the engine somewhat to drivers side. Am I AFU?

 

@gearcruncher sorry to call you back into this...

So I bagged the vent and put a diaper on the trans pan seam. Without a doubt the fluid is coming from the vent. Running hard and lugging the engine in drive I'm getting 208 in the TC, 180's in the main sump, so I'm inclined to think it is not temperature related. During the tranny fluid exchange the outlet of the heat-x was flowing strong, so I'm thinking no blockages.

Foaming fluid...Hmmm? What could cause this. Is it possible this knucklehead left the old filter o-ring in place and now I have two stacked resulting in a bad seal that is picking up air on the suction side and causing foam? Damn, sounds like another pink bath in my future.... Anything else I can eyeball when I'm in there?

 

What are we working with for mileage ?

 

120k

 

Ive seen a few transmissions not have the O-ring on the filter and foam the fluid but it didnt come out of the breather. The only time ive seen fluid come out of the breather is when the tranny was over filled.

 

I'm 99% sure it is not over filled (not sure I'm 100% on my own name at the moment). I understand the temp constraints when filling and use an OBD II reader to get the required temp. With correct temps it would be damn near impossible to overfill. But - I will check again when I dig back into it.

 

With 120K on the truck , we also dont know the history the previous owner had with the truck such as how long has this been happening and was the transmission run dry on multiple occasions ?
The circuitry in the valve body that controls the vent could be damaged or stuck partially open . The valve body could also be loose ?
There are a few things inside the transmission you may have to visit to get the vent to stop leaking .
I would suggest doing as much as you can from the outside before venturing into the valve body .
I am wondering how difficult it would be to figure out when the vent leaks and how much fluid you are actually losing when this happens ?
Are you losing fluid through the vent at idle or as the truck is running and hot ?
Can you confirm your torque converter is functioning correctly .
Can you re-route the vent line or extend the line to prevent that fluid from hitting your exhaust

 

As stated, I have no history. I exchanged fluid as part of new owner general precautions. I suspect it was the first fluid change. My impression at the time was that it was low by several quarts.

It seams to leak when it has been run hard and the TC is getting abused in Drive - I live in a hilly area. I had the vent bagged for a week and appear to have about 2 tablespoons of fluid in it. Not a perfect seal so it has been leaking and dripping - so I'm guessing total leakages is maybe twice that amount. I don't think it is "puking" fluid, I suspect it's much more of a seeping/burping(?) type of event - total speculation.

How do confirm TC is operating correctly? I this the "tap the breaks at speed" and drive check that I downshift into 4th - or something along those lines?

It's tight, but I bet I could snug and clamp a line to the top of the vent to re-route and capture what is coming out. This might make it possible to see if it is foaming or solid fluid coming out. Interesting idea. Would help with the mess if nothing else!

Not knowing the current fluid level, I'm inclined to get things topped back off correctly and go from there.

 

If you are living in a hilly area and your converter is locking and unlocking on a constant basis , you may be getting temperature spikes that you dont get to see on your OBD scanner .
Have you considered throwing a bigger cooler at it ?
The tiny cooler thats situated up front is very small .
Not sure if you tow , run in 4 wheel low often or a lot of stop and go traffic , but an aftermarket cooler may be one fix to alleviate the leak .
Kill 2 birds with one stone .
https://www.tacomaworld.com/threads...l-toyotas-write-up-with-many-pictures.526283/

 

As it turns out, I own another 2010 CCLB as well. Same basic mileage. I run a Tru-Cool on it per your recommendation - thank you for that. I have it rigged with 600+ lbs of camper, sliders, bumper, winch... I run an ultragauge with TC and Trans Temp on the first page and actively manage temps as needed via the shifter. Very pleased with how the setup works. The truck in question is my wife's grocery getter. Watching the OBD bus in near real time it looks like it runs a bit cooler and responds quicker than my other setup, which makes sense considering the lack of load. It likely has a Tru-Cool in it's future just for good measure, but it appears pretty happy as is - with winter temps at least.

 

@gearcruncher

Still Chasing... To get myself back to ground zero, I ran the transmission to temp and checked the level. As expected it was low. I drained the trans and dropped the pan. I recovered just over 7 qts. If memory serves, i should have something like 4 qts in the cooler and T/C for a total of 11 Qts in the system leaving me ~3 qts short. I verified that the filter had just the one o-ring. Checked the valve body bolts and all were tight. I've added a length of tygon to the vent to get a better view of what is going on there. Is there anything else I can do before I button the pan up and bring the fluid level back to spec?

v/r

 

I think you covered everything I would have done to try and figure out the issue .
Awesome job .
Keep us updated . Your issue is rare indeed