6R140 puking ATF when cold

D60

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Where is the vent on the 6R140?

I've recently discovered mine occasionally pukes fluid when moving it around in my driveway. The fluid comes from the top near the very rear. It runs down the right side and winds up on the rear row of pan bolts. It's not pan gasket.

In carefully thinking about mysterious trails and puddles on my gravel drive (which I wrote off to other vehicles), this has been going on awhile. It drives fine and shifts as it always has.

I checked fluid level today after some highway driving and it's just at the very bottom of the dipstick, so probably down ~1qt

I kinda suspect this wouldn't happen if I always just drove it. Seems to happen just from starting and turning around, like backing into the shop. I also suspect Reverse is required to make this happen, but can't swear to it.

But then again, I'm assuming the vent is near the rear. If not, I have a leak/burp from somewhere else....

@clinebarger @mattd
 
Is it coming up the fill tube? Wonder if it's due to fluid being thick & using reverse increasing pressure causing it to eject some fluid?
 
Vent is at the top in the front. There is nothing back there up top unless it’s running straight back, which would be unusual. All the speed sensors are inside the case. I don’t see how the fluid would get that high in the case just moving it around cold. Any photos? The only external leak I can think of at the back that’s not the output seal is the Allen plug for the parking pawl pin but that’s toward the bottom above the pan in the back.
 
Vent is at the top in the front. There is nothing back there up top unless it’s running straight back, which would be unusual. All the speed sensors are inside the case. I don’t see how the fluid would get that high in the case just moving it around cold. Any photos? The only external leak I can think of at the back that’s not the output seal is the Allen plug for the parking pawl pin but that’s toward the bottom above the pan in the back.
Thank you. The plot thickens. I'll have to get it on the lift and investigate more and maybe fire up the inspection camera

Also I don't know if it's related but this trans used to "drop out" of gear when cold and first started. If I let it warm up even a minute or two it seemed to avoid that. I used a bottle of the Seafoam transmission stuff and it seemed to decidedly cure it. I then did a spill 'n fill to get rid of most/some of the product.

Thing is, I don't know where in the timeline it started this mysterious fluid loss. Maybe it was doing it well before dropping out of gear, maybe after that stopped....maybe zero connection at all.
 
Thank you. The plot thickens. I'll have to get it on the lift and investigate more and maybe fire up the inspection camera

Also I don't know if it's related but this trans used to "drop out" of gear when cold and first started. If I let it warm up even a minute or two it seemed to avoid that. I used a bottle of the Seafoam transmission stuff and it seemed to decidedly cure it. I then did a spill 'n fill to get rid of most/some of the product.

Thing is, I don't know where in the timeline it started this mysterious fluid loss. Maybe it was doing it well before dropping out of gear, maybe after that stopped....maybe zero connection at all.

Does it drop out of reverse, drive, or both? What year truck?
 
Does it drop out of reverse, drive, or both? What year truck?
It's a 2011 (vehicle built March of '11 per ETIS) and as I recall it was dropping out of either D or R. Just low speed moving around my driveway, like flipping around and backing into the shop.

It would go to limp mode and just restarting would cure it.

Kinda suspected something with excessive converter drainback overnight, but that wouldn't really explain how Seafoam could help that.

But if there's still something with excessive drainback it could maybe also explain puking fluid?....maybe?....but wouldn't really explain why it now moves and is no longer dropping out of gear if the converter is empty or mostly empty.
 
Not that this relevant but… GM THM-400 trans would push fluid out of the dipstick tube if they were running low in fluid. Doesn’t make sense but, the thought is that the pump would grab the fluid in such unsteady “gulps” that it would churn fluid everywhere.
 
IIRC there was an issue with the early build pumps allowing drain back while sitting that could very well be your issue. But it should resolve itself quickly, within several seconds of putting it in gear it should move and then not drop out.

Even if that was the case it shouldn’t drop out once it reprimed. And it would have to be grossly overfilled for it to come out the top of the case. And if the vent was plugged it should be coming out the front and rear seals I would think too.

Has the filter ever been changed on the truck?

Tired piston seals could also be an issue but a little too coincidental for both forward and reverse. Another thing to check would be internal valve body leaks.

I would see if you can pinpoint that leak before anything else.
 
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