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Drivetrain - 2001 - 2010 Discuss front and rear axle, transfer case, brakes, etc. Transmission questions belong in the appropriate transmission forum below. First through fourth generation... is the premier Duramax Diesel Forum on the internet. Registered Users do not see the above ads.
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Old 07-15-2011, 12:53 PM   #1 (permalink)
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Allison 1000 blowing atf out of the vent

I have a 01 duramax with 5spd allison 1000. When I take my truck on the highway it blows atf all over the bottom of the truck. When I'm in town it does just fine. It never over heats. When it sits it leaks fluid from which looks to be the vent on the top and by the transmission filter. When I check the fluid cold it is in the hot zone and when the transmission is hot it is in the cold zone. I followed the correct procedures in the book. I took it to aamco and they said my pressure test was out of spec. I need a complete overhaul. I've heard that it might be that the pump assembly needs to be updated , along with new springs. I've read other peoples diagnosis that the transmission is too full. I can't afford a couple grand to fix it, I might pull it myself. Not sure how to rebuild it. Any info would be appreciated.

Thanks, Brandon

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Old 07-16-2011, 08:19 PM   #2 (permalink)
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I would post this in the tranny section for quicker replies.

06 LBZ ECSB, 285 BFG All Terrains, 4" Flowmaster cat-removed, modified air-box with stock filter, Predator on 120hp tune, Kennedy tie rod sleeves, bedliner, window visors, 8' Fischer plow, 8' home made back plow with down pressure, tinted windows and Prodigy brake controller.

Sold, 06 LBZ RCLB, 285 Cooper Discoverer ST's, 8' Fisher plow, Line-X liner. Truck will be missed!

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Old 11-23-2011, 08:49 AM   #3 (permalink)
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I have the same problem it seems. I found this It may help.

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)

The extra length of the tube will allow the expelled fluid to be trapped and later drain back into the transmission.

In addition, on 2001-2004 models, replace the transmission fluid indicator (dipstick) with a new vented indicator.

Refer to bulletin #10-07-30-001A for additional information and installation procedures.

- Thanks to Al Ferry
2002 Chevy Crew Cab D/A SB/4X4
Transfer case upgrade
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Old 11-23-2011, 11:32 AM   #4 (permalink)
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I never did understand why on any transmission they even have a vent in the case. Should just use a vented dipstick and be done with it.
2005 D-max w/5-Speed Ally 2WD Chevy Silverado 2500HD, CC/SB LS - SOLD 3/17/16.

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