Transmission Pan Gasket Leaking

Greetings,

I have a 2005 2500 Duramax and I've tacked down a transmission leak at the pan gasket. My choices to fix it: Take it back to the guy who serviced the transmission 15K ago... or replace the gasket myself.

I'm pretty handy but I've never touched a transmission pan. Is it as easy as it seems? Drain oil... drop pan... replace gasket? Is there something I'm missing?

I know this is such an easy rookie question... I'm just looking for responses like: Don't Do IT!... you might do... this... and break that.... Or.... yes... it is that easy.

Thanks in advance.

Richard

Welcome aboard!

You shouldn't have to replace the gasket, and the pan shouldn't have been removed for service (Allison recommends pan removal and internal filter service only at overhaul). The gasket is reusable rubber, and should survive at least one R/R, typically several. If it was removed, it's likely to have been improperly tightened, over, under, or unevenly torqued. Before removing, inspect and compare the gasket distortion and bolt torque in the area of the leak, and areas it is not leaking. It may only need tightening. If it's overtight where it's leaking, it will likely need pan removal/repair, and perhaps a new gasket if it's damaged. If/when you drain the pan, it will take just short of 2 gallons ATF to fill it again.

Also check for leakage at the vent on top. If you have an overfill or overheat condition, it can leak some fluid (trickles down the case, and drips off the pan). It can also leak if you have a torque converter drain-down condition (converter drains fluid while sitting idle for a period of days, causing "overfill"). The drain-down is much less common in later models, compared to 2001-2003 models, but can happen.

Take your time with dropping the pan as it will start to hang when the bolts are loosened. You can do it numerous ways, but essentially you need 3 bolts to keep it from dropping and then you can spin these 3 out while holding upward.

Look for simple grit in the gasket bewteen the ribs. Also check that the gasket is OE and not some cheap aftermarket cork piece of crap. The OE gasket is a rigid, ribbed, rubberized piece with grommets where the bolts go through.

Quote:

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Originally Posted by DmaxMaverick

Welcome aboard!

You shouldn't have to replace the gasket, and the pan shouldn't have been removed for service (Allison recommends pan removal and internal filter service only at overhaul). The gasket is reusable rubber, and should survive at least one R/R, typically several. If it was removed, it's likely to have been improperly tightened, over, under, or unevenly torqued. Before removing, inspect and compare the gasket distortion and bolt torque in the area of the leak, and areas it is not leaking. It may only need tightening. If it's overtight where it's leaking, it will likely need pan removal/repair, and perhaps a new gasket if it's damaged. If/when you drain the pan, it will take just short of 2 gallons ATF to fill it again.

Also check for leakage at the vent on top. If you have an overfill or overheat condition, it can leak some fluid (trickles down the case, and drips off the pan). It can also leak if you have a torque converter drain-down condition (converter drains fluid while sitting idle for a period of days, causing "overfill"). The drain-down is much less common in later models, compared to 2001-2003 models, but can happen.

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Thank you so much for your response.

I'm convinced it is leaking from the pan as I can wipe away the area and press paper towels all around it to soak up anything that could be coming from above.. and it leaks. Also, it seems to leak down to level of the gasket... when the leak seems to stop and I check the fluid level hot the fluid shows on the stick in the cold range. Then I add a quart and the leak increases.

I don't know if the gasket was replaced when it was serviced. I'm not likely to use the guy who serviced it as I'm not trusting him a lot (other things with other jobs. The bolts seem to be cranked down quite tight so I don't think they were loose. However, they certainly could have been overtightened if the gasket was replaced.

Again, thanks for your help.

Richard

Quote:

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Originally Posted by Kennedy

Take your time with dropping the pan as it will start to hang when the bolts are loosened. You can do it numerous ways, but essentially you need 3 bolts to keep it from dropping and then you can spin these 3 out while holding upward.

Look for simple grit in the gasket bewteen the ribs. Also check that the gasket is OE and not some cheap aftermarket cork piece of crap. The OE gasket is a rigid, ribbed, rubberized piece with grommets where the bolts go through.

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Thanks for the tips.

Richard

Well that was easy. I could not figure out why the gasket was leaking. It looked fine. It did appear to be OEM. I replaced it and all is well. Thanks to all.

Richard