What did you do to your NNBS GMT900 Tahoe/Yukon Today?

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992dr

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I was kinda being facetious about it being easy. Unbolting the bellhousing is the biggest PITA of the job. You really wouldn't have to drop the trans. "Just" unbolt (or remove) the starter, remove the plastic shield, remove the three flexplate-to-converter bolts, unbolt the driveshaft, unbolt the rear trans mount, remove the eight bellhousing bolts (some will have nuts on top of them that hold other items), disconnect the trans cooler lines from the trans, pop out the trans dipstick tube (one of those items secured by a nut on the bellhousing bolt/stud), might have to unplug a harness(s) or release it from the clips for slack, then support the trans with a transmission jack or some other that can roll, then slide the trans backward a couple inches.

You'll need about 4' of extensions with U-joints and/or wobble extensions to reach some of them bellhousing bolts from the back of the trans.

The material of the alignment tool isn't much concern for you. If you were a shop that worked on a lot of LSs, then you'd invest in a billet one. Honestly, I've never used one. I use the crankshaft to center the cover, then a straightedge to align the bottom of the cover with the bottom of the block, letting it pivot on the crankshaft. This is easy to do with the engine out, but with it in the vehicle and with limited working space, the alignment tool will pay for itself in labor. All the covers (oil pan included) have to be aligned within very tight tolerances. The oil pan has to snug up to the block and bottom of the front and rear covers, so those covers go on first and have to be in proper alignment. The bellhousing snugs up to the rear of the block and to the oil pan, so the oil pan has to be in proper alignment. You don't wanna have the bellhousing pushing or pulling on the oil pan cuz it can crack it. Yes, there are two long bolts that secure the oil pan to the rear cover. These are the two that get torqued to a much lower spec than the rest of the oil pan bolts (106 in.-lbs. versus 18 ft.-lbs.)

Any chance your rear main seal is ok and it's just your oil pan gasket leaking? Have you tried cleaning off all the oil and watching for fresh trails to find the source? Grab a couple cans of Super Tech brake parts cleaner from Walmart and spray off the oil. Don't forget the safety goggles!

Yeah, kinda figured that hahaha. Thanks for all the info, it is something I'll be definitely doing a ton more research before tackling. I appreciate the info that's for sure.

I'll have to inventory on my extensions and universal joints haha just to make sure I have enough to reach back there haha.

I'll grab an alignment tool.

Good question. I was hoping it was the pan gasket or the oil pressure relief valve. When I had my car on the lift my mechanic was pointing out oil up on the starter and other spots up there and said it has signs of the rear main going from the oil spatter. I will grab some break cleaner and douche it down thoroughly and try to keep an eye on it. Its touch to get under there with it so low haha.
 

iamdub

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I was hoping it was the pan gasket or the oil pressure relief valve.

Oil pressure relief valve is inside the oil pan and pops open when AFM engages. The oil sprays inside the pan and not anywhere outside. Well, I guess you could consider the one in the oil pump a relief valve as well. Regardless, if either of these are causing an EXTERNAL oil leak, then you have some serious problems!


When I had my car on the lift my mechanic was pointing out oil up on the starter and other spots up there and said it has signs of the rear main going from the oil spatter

It's kinda difficult to see, but grab a bright flashlight and a small flathead screwdriver. Pry out the round hole plug (inspection cover) and shine the light up in there. Aim it between the flexplate and engine block. Look for oil trails coming from up near the crank.

Here's an interweb pic of the flexplate as seen through the hole with the cover removed:

aac19d21a127dafb27e72f31852ce3b2.jpg
 
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