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Discussion Starter #1
Today at 1100 miles I noticed the Allison trans pan had a "wet" area on it. A closer inspection revealed that there were 2 or 3 drips forming on the front and rear trans pan bolts. The garage floor had about 2 teaspoons of ATF on it. The regular parking spot at work had the same. The trans pan gasket looked wet all the way around. There is no ATF anywhere on the trans above the pan gasket. There is no ATF around the vent pipe. I re-torqued the trans pan bolts to 20 ft lbs. None of them appeared to be loose. The filter is not loose. There is no sign of any ATF running down the dipstick tube.


I reviewed the TSB's and I didn't see anything that mentioned just a slight leak. The trans does not make any abnormal noises at idle or in motion. I cleaned all surfaces and will look for the leak point in the days to come. I'm hoping it may be a bad pan gasket, but I've never seen a new gasket fail. Does anyone have any ideas about this problem? Has this happened to anyone else?
 

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My 2004 HD2500 LS 4x4 LLY Allison is in for service now. Lost 2qts of ATF in 1350 miles. I undercoated my truck with Dextron.


They think its a failure of a new rubber seal Allison is using.
 

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Discussion Starter #3
ekrott


Where was the ATF leaking from? The torque converter housing (in front of the spin-on filter)?
 

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Dura_Mike
First wipe off the area in mention. Place vehicle over kraft paper in the transmission area. Start vehicle up in park, let vehicle run for 15 mins. Shut vehicle off, if on a lift, check area of the transmission leak if it is bolts mark each one with a marking pen.(fluid will be hot)Remove one bolt at a time and wrap with teflon tape , torque to factory spec's. Wipe area off an recheck
 

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Discussion Starter #5
GMC-DMAX


Thanks for the tip. I will keep an eye on the pan bolts.


The fluid appears to be very slowly seeping past the pan gasket on the driver’s side. It looks like it is running along the pan and collecting on the back 2 pan bolts. I meticulously checked all vertical areas around the trans case and it’s dry. I can see the gasket itself between the case and the pan and it looks wet. When I fold a paper towel in half and press it into the gasket, it picks up a small amount of ATF fluid. The factory torque setting on the pan bolts is 20 ft lbs. I set the torque wrench to 23 ft lbs and went around the pan again. I won’t torque the bolts any tighter than that for fear of warping the pan. I wonder if the NSBU switch could be could be where the leak is? There is some mechanical linkage between the switch on the outside and the internals. There is probably a seal there. I wonder if that seal could be the problem?
 
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