Hey friends,


Noticed my 08 Tahoe (117K miles) was super low and oil so topped it off and peaked underneath. The bottom of the pan, transmission bell housing and other areas were covered in oil, and there were also three large drops waiting to drip off. From my experience with GM/LS engines I'm sure I'm dealing with a rear main seal leak, or possibly a oil pressure sender on the top side leaking oil down.


On any other GM car/truck with a 4L80/TH400/T56 transmission I could drop the transmission with my eyes closed, but on this one (2ML70 I believe) I know it is quite different from a standard transmission, including the high voltage lines connected to the side of it. Other than reading through my GM manual, any other tips/words of advice for dropping this transmission to check out the rear main seal?

 

It's not rear main seal. There is a TSB for engine porosity making it leak. I think there is a gasket that needs to be replaced.

 

Ill see if I can find it, that would be much worse but I know it happens. Im guessing the TSB if for the rear cover gasket.


My main concern is being able to remove this transmission, since it has the high voltage lines... I really don't want to kill myself here disconnecting those. But I cant find much information online about how to remove it properly.


Once again... I regret buying a hybrid somewhat due to the fact I cant wrench on it easily like my other GM vehicles.

 

Search in my older threads. I started it way back in 2009/2010. The TSB should be there. It is common in hybrids and non-hybrids. I think the dealer just replaced the engine oil sump and it seemed to fix the problem. Since I noticed the leak when it was new, I did not want them to tear the engine down. It never needed oil in between changes hence decided to have it fixed at 100k miles.

 

You won't believe the suggested repair for engine porosity? Not a new engine but the application of JB weld. I didn't know JB weld is mainstream.

 

Pretty crazy, I've heard of people using that or applying some rtv if the porosity is under a gasket lol.

 

I think there is a turn off switch so you will not be electrocuted.

 

There is a Manual Service Disconnect on the passenger side of the HV battery. That needs to be removed before you go putting wrenches on those 3-Phase cable attachment bolts.


That transmission is one BIG heavy one. The two big permanent magnet motors weigh plenty.


So a very good transmission jack is in order.

 

Check the oil pan gasket, I had to change mine when I had the same symptoms. We actually had to use dye to find the leak and the mechanic was still in disbelief that it was just the oil pan gasket. Hasn't leaked a drop in 40K miles since.