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Leaking ATF from Allison 1000

37K views 25 replies 9 participants last post by  starspangled6.0 
#1 ·
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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#3 ·
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.
 
#5 ·
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
 
#7 ·
I was also wondering if it might be coming out a vent.........
 
#8 ·
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?
 
#13 ·
the allisons up to 2006 are prone to mild leaking in colder conditions, i used to do the remote starts for a northern alberta gmc dealership, also did dodge and fords, we would get the dmax's in out of the cold and when they warmed up there would be a small drop on the floor, id say 5 out of 10 were like this and if im not mistaken gm had a fix for this, maybe only in canada tho im not sure
 
#16 ·
Huh. There does appear to be fluid coming from above the pan, and so that would explain it. How cold did it have to be? The coldest it got yesterday was in the low 30's (maybe high 20's with the windchill).
 
#17 ·
we would see this on brand new trucks keep in mind, so it makes sense that it could happen on a older truck thats being worked hard, id go talk to a dealer because i know for fact they had a fix in canada for this, and it looks like you have the exact same thing happening with yours.....could just be a bigger oring maybe who knows lol id say
0-minus 40f would be the range, like i said tho these were brand spanking new trucks
 
#18 ·
i just talked to an old friend of mine who worked at the dealership at the time and he said it was usually one of the wiring harness plugs that was the problem but sometimes it was other seals like the linkage and cooler line o rings, hope this helps you out man but im pretty sure its just gonna come down to a lil rubber oring someweres
 
#19 ·
OK, thanks for the tip. The o-ring leak makes more sense then the pan gasket. I'll give it a good look-over today.
 
#20 ·
One of our work rig's did the same thing, Dealer replaced the seals on the wire harness. We were towing a bobcat for a builder friend of ours and it left a couple of drips on the floor the next day, once fixed it never did it again.

LGSONE
 
#22 ·
So... I saw the vent at the top of the tranny today. I don't see how, if it was coming from a leak where the shift linkage hooks up to the tranny, it would be able to spray on the driveshaft going to the t-case. It makes more sense that it was just venting, but that bulletin Mike posted said it had to be below 0 degrees, and it was above 30 degrees when this happened. Weird.

*EDIT*

It may be an issue with an overfill... http://www.duramaxforum.com/forum/trans ... fluid.html

There is no conclusion to this post, but he's got the exact same issue as me, and it looks like he's over-filled it. Once it gets hot, it pukes a little bit of oil through the vent. I'll have to check my fluid level again...
 
#23 ·
The pictures initially posted look EXACTLY like what is going on with my Allison. The issue described is nearly identical. I have owned this 100,000 mile truck for only 3 weeks but this started shortly after purchase. It has been cold here in KS recently but not below 0F for long. So far my transmission has never reached 150F, is that abnormal? It doesn't leak often and I never can see it leak fluid when I am underneath it running. I park on dirt so it is hard to tell if it is leaking, plus I made a GIANT mess when replacing the trans cooler lines (which SUCKED, should have went with the aftermarket hydraulic lines) I would swear it was a pan gasket issue however the pan is supposedly not under pressure. It is "spraying" the front driveline and shifting assembly. I cannot see a vent anywhere. Plus, isn't the vent fix/new dipstick tube for 2001 to 2004 Allisons? I am concerned that is coming from the vent of the transfer case, which would indicate an issue with the rear transmission seal, right?

I would say it too could be an overfill problem, however I cannot get the trans temp up enough to do a hot check. Current when it has been running for an hour the fluid is in the middle of the hot checked area. PLEASE help me. I have not found a good mechanic here yet and really cant afford to pay someone to stumble into a solution for the issue. Thanks and sorry to hyjack.
 
#24 ·
Ever since I switched to AMSOIL fluid, I haven't had an issue at all. Synthetic will perform way better then conventional, and it's possible the fluid level changed since the mechanic took fluid out and put fluid in.

The Allison, from what I know (which usually isn't much :lol:), will run really cold, or really hot. In the winter, if I drive around with the plow off, it will only get barely past 100 degrees. However, in the warmer months the transmission is quite happy running in the 200-230 range.
 
#26 ·
The method my mechanics used was to unplug one of the cooler lines, and then run the truck. You add as much as comes out, until the fluid coming out is the same color as the ATF going in.
 
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