Allison leak top of tranny on rear

briencolgan

briencolgan

brien colgan
Jan 26, 2017
85
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8
Ithaca, NY
The subject says it all. Tranny fluid is leaking out as fast as I can port in and there’s some sort of fitting her seal on top of the unit about where the driveshaft Connects on top.

I think this is related to excessive pressure in the transmission as I was carrying a heavy load of soil in a dump trailer. The truck got home fine sat in the driveway for a few days but then when I back it up to drop the trailer I got nothing and drive and then saw the massive of fluid leak.

Anybody know what that is?


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Bdsankey

Bdsankey

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The only port on top of the trans is a vent on the back of the main case (middle section). Are you positive it's coming from the vent while you're pouring trans fluid in it? How full is the trans according to the dipstick?
 
JoshH

JoshH

Daggum farm truck
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The only thing on top toward the rear that can leak is either the case vent like Brad said (which cannot leak unless it is way overfull) or the extension housing could be cracked causing a leak. Usually when those crack, they leak from the cavity where the C5 piston gets pressure; it will typically leak whenever the engine is idling and will be a pressurized spray of fluid.
 
Chevy1925

Chevy1925

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briencolgan said:
It’s totally empty I’m pretty sure.


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look, not trying to be an ass, this is all text so dont take this the wrong way but think about this for a minute.

you are telling us its leaking out of the TOP of the trans but the pan is dry/no oil on the dip stick. the pan is at the very bottom of the trans. It makes 0 sense that oil would be coming out of the top of the trans.

what i would guess has really happened is, the truck is parked somewhat up hill, you cracked the extension housing from the heavy load and a bad u-joint (very common) and now its leaking alot of the fluid out of that housing crack.

you have to get under there and dig a little deeper and paint us a better picture. we arent there to see whats going on.
 
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Chevy1925

Chevy1925

don't know sh!t about IFS
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JoshH said:
The only thing on top toward the rear that can leak is either the case vent like Brad said (which cannot leak unless it is way overfull) or the extension housing could be cracked causing a leak. Usually when those crack, they leak from the cavity where the C5 piston gets pressure; it will typically leak whenever the engine is idling and will be a pressurized spray of fluid.
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tree'd... f**ker lol
 
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Bdsankey

Bdsankey

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briencolgan said:
Whatever it is feels like a little plastic E in it kind of wobbles around up there.


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That would likely be the vent then as it is free to spin as it is a tube with a "cap" to keep debris out it.

Like James and Josh said, it is impossible for the trans to leak out of the vent IF it is actually empty.

Is the truck pouring fluid out of it when you try and fill it while it is off or just while running? If it is just while running I would bet (like James and Josh stated) you likely have a cracked extension housing.
 
K

KyleC4

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Dec 30, 2016
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Only thing that makes any sense to me here is that the dipstick tube broke and that’s why he saying it leaks out as fast as he pours it in. Engine should not be running when adding fluid to trans that is empty so that is why I’m guessing not a cracked extension housing.

And don’t be sorry or worried for sounding or coming off like an ass James. This is one of those type of posts where people don’t need to be coddled. ”It’s totally empty I’m pretty sure” ………. Technical quote of the Year
 
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briencolgan

briencolgan

brien colgan
Jan 26, 2017
85
4
8
Ithaca, NY
Now go figure. Not a bolt was turned. Started up the truck and it runs great. Road tested. No leaks. Nothing. Why? Why?


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1FastBrick

1FastBrick

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Dec 1, 2016
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briencolgan said:
Can they leak from the pnp switch?


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I think there is a seal on the side of the case but I wouldnt expect it to come out the way you mentioned in the first thread. It my form a drip over time if it was worn. But there wouldnt be pressure behind it.

If the dipstick tube case seal was compromised, I could see it gushing out as you poured it in...
 
briencolgan

briencolgan

brien colgan
Jan 26, 2017
85
4
8
Ithaca, NY
Chevy1925 said:
look, not trying to be an ass, this is all text so dont take this the wrong way but think about this for a minute.

you are telling us its leaking out of the TOP of the trans but the pan is dry/no oil on the dip stick. the pan is at the very bottom of the trans. It makes 0 sense that oil would be coming out of the top of the trans.

what i would guess has really happened is, the truck is parked somewhat up hill, you cracked the extension housing from the heavy load and a bad u-joint (very common) and now its leaking alot of the fluid out of that housing crack.

you have to get under there and dig a little deeper and paint us a better picture. we arent there to see whats going on.
Click to expand...

I’ve been under. I can’t see crap. It’s so wet with tranny fluid. The local Allison whisperer thinks it’s a cracked housing too. So that’s prob it.


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