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Leaking ATF from Allison 1000

Fluid leak after running hot

Leaking ATF from Allison 1000

Postby starspangled6.0 [OP] » Oct 27 2012, 1:07am

We ran the Silverado hard today, towing the trailer with the plow on (note to self- not a good idea :oops: ). Going up hills, the engine times would do about 220-230, and the tranny temps would go past normal (185-ish) to a little over 200. When we shut it down for the day, the tranny temps were just over 200. While we were unhooking the trailer, I noticed some droplets under the tranny pan, and sure enough, it was fresh ATF. It looked like some was coming from the pan gasket, but it was also on the driveshaft for the transfer case, as if it was spraying out of the transmission somewhere. The pics aren't the greatest, but it's the best I could do at the moment.


It's never leaked before from the tranny. I've never seen drops of any kind since I got it in September, but this was the hottest we've ran it. There was also a couple of drops coming from the oil filter on the engine, something I've never seen before; almost like someone didn't tighten it all the way. Once the truck cooled down, it didn't drip anymore (and we're talking just a few droplets total, not puddles). The tranny fluid looked fine, and smelled fine, too.


Any ideas? Should I expect this to happen every time it starts to overheat (and LLY Duramax engines are known for running hot at times)?
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Leaking ATF from Allison 1000

Postby WrensLawnCare » Oct 27 2012, 1:30am

Hmmm that's odd. I don't have an Allison not the Dmax but my 4L80e runs about 200-210 when in pulling my trailer And I pull it all over the place. Mainly in traffic around town. Never noticed it leaking though and it has some miles. Maybe a seal or converter?
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Re: Leaking ATF from Allison 1000

Postby starspangled6.0 [OP] » Oct 27 2012, 1:34am

It seemed to come from the tranny pan seal, maybe it got so hot it sprayed out? It was above the tranny pan seal, so either it did spray out, or it's leaking from somewhere above the seal.
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Leaking ATF from Allison 1000

Postby WrensLawnCare » Oct 27 2012, 1:46am

Maybe try spraying/wiping it all off, then let the truck run for a bit to get the trans warmed up some and watch for any leaks? Leaks can be a PITA at times. Good thing is, not many places trans fluid can come from.
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Re: Leaking ATF from Allison 1000

Postby Z15 » Oct 27 2012, 12:19pm

Does this sound like it could be it?


Allison Transmission Fluid Leak

By Blog Post on March 1, 2010 11:00 PM| No Comments

During cold weather, a small, red fluid leak may be noticed on some 2001-2010 Silverado and Sierra 2500HD-3500HD series models equipped with the Allison LCT1000 transmission (RPO M74, MW7). The fluid leak may be at the back of the transmission by the vent.



This condition may be caused by fluid being discharged out of the transmission vent during extreme cold weather (approximately -15°F or -25°C or colder), at which point DEXRON® VI and other conventional transmission fluids become extremely viscous.



When the viscous fluid is circulated into the vent area, it becomes trapped and is not able to drain back to the pan. As the transmission warms up, the expansion of the air inside the transmission can force the trapped fluid out of the vent, leading to small drops of fluid being discharged.



To correct this condition, remove the stock vent assembly and run an external tube (Fig. 2, A) and vent (remove the top of the vent assembly) (Fig. 1) up to the front of the transmission to a mounting bracket. (Fig. 2, B)


http://www.archivedsites.com/techlink/2 ... -leak.html
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Re: Leaking ATF from Allison 1000

Postby manicmechanic1961 » Oct 27 2012, 12:52pm

Rear seal should leak worse when cold not hot. Most likely culprit was vibration, plow and trailer combination. Remove both plow and trailer, clean output shaft seal area, take vehicle for a good run and re-examine. Driveshaft u-joints?
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Re: Leaking ATF from Allison 1000

Postby Hartski » Oct 27 2012, 1:22pm

I was also wondering if it might be coming out a vent.........
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Re: Leaking ATF from Allison 1000

Postby starspangled6.0 [OP] » Oct 27 2012, 5:12pm

Thanks for the advice, guys. Looks like it's either a venting issue, or the pan gasket is bad. I checked again today, and there were a few drips, but those may be leftover from yesterday (I didn't clean anything yesterday). When I checked the fluid yesterday, it was pretty runny (typical ATF), but it seemed a little on the bubbly side, too.

I cleaned off the pan today, and after driving it hard for a while, no drips (temps stayed below hot, since the trailer is off). Can that fluid vent, even though it was only in the 30's yesterday?
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Re: Leaking ATF from Allison 1000

Postby dmaxfireman » Oct 28 2012, 12:23am

Check your dipstick, see if it popped out of the grommet. Seen that happen more than once when torquing up steep grades if it was loose to begin with.
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Re: Leaking ATF from Allison 1000

Postby starspangled6.0 [OP] » Oct 28 2012, 2:00am

Dipstick was fine; we checked it once we finished for the day.
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