Ever seen this? Not the motor mount either

My son called me because the new to me truck, 2007 Chevy Silverado Classic 1500, 204k miles, was making a racket when moving. He pulled into a parking lot and saw oil pouring out of the transfer case. I had it towed home and while it was up on the truck, I looked at the transfer case and found that the transmission mount had collapsed, the transmission and transfer case had dropped down and the U-joint of the front drive shaft was hitting the frame cross member. The transfer case is also resting on the cross member.

The cross member appears to be U shaped so I’m thinking (hoping) that it might have worn a small hole in the case instead of a big crack and that I can fix it with some JB Weld. I’m also hoping that all I need is a new transmission mount. Right now it is getting very cold outside so it looks like I won’t be getting any cooperation from the weather soon.

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I like using JB weld for some things, but this would not be a place I would rely on it.

I’d pull the transfer case and take it where they could weld a piece of aluminum over the hole, if it’s not too big a hole.
I’d worry though if there were pieces of aluminum in the bottom of the transfer case.


I haven’t had a chance to check it out yet but there is no pressure inside this case so I would trust JB Weld as long as there aren’t any cracks. Any cracks and I will get a reman transfer case. It’s GM so it will be a PITA to replace. I’ve seen the YouTube videos.

I am confused by your post and the answer. Did the trans mount fail and then wear a hole to the T-case. Or is there a hole in the T-case independent of the crossmember? These 246 transfer cases are notorious for wearing thru the case and leaking fluid. Seeing as how they only hold about 2 quarts, that can kill the case very quickly if not addressed. There are aftermarket rear housings that will fix that for less than the cost of a reman case.

As for the crossmember. No JB weld is gonna fix that. Real weld is needed.

The trans mount is an easy swap though.

The transmission mount failed/collapsed so the transmission and transfer case dropped down to where the transfer case is sitting on a frame cross member. There are two cross members here, on that is removable that the transmission is mounted to, it looks like the rubber of the transmission mount failed here. The transfer case is sitting on the top of the cross member that is right behind the transmission mount and the U-joint is hitting that cross member when it spins.

I understand that when transfer case develops a hole, it is from the chain but I’m not 100% sure about that.

If the chain is so worn out that it has rubbed a hole in the case there won’t be any patching it up I don’t believe. Maybe when you support the transmission and remove the crossmember the damage will be visible.

Yeah if the chain wore a hole in it, I’d be getting a reman for sure.

BTW, since the transmission mount collapsed, I will be checking the motor mounts as well. Since its a Z71, I wont need to use any jack stands to hold the truck up. There’s plenty of room under there.

If you’re lucky it’s just the seal leaking at the u-joint yoke going into the transfer case

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Didn’t think of that. Hope it warms up enough tomorrow for me to get under there.

Yes, the chain can rub through the case if it is very worn BUT there is a thrust surface inside the T-case that can wear through as well. As you look to the end of the case from the rear of the truck it is upper right.

Mine was leaking but had no visible hole. Everything else int he T-case was fine so I just had the rear housing replaced. It still required removal.

Crawled under there today, it’s not the transmission mount like I thought, it’s the drivers side motor mount. I can’t see it because of the front differential, but every thing leans downward on the drivers side.

I have a cherry picker, but it is at my brother in laws. I’ll have to borrow his truck to bring it home. I think that first I will look for a jack point, maybe I can jack up that side of the engine but it isn’t looking promising, theres a lot of stuff on that side.

I don’t see any holes in the transfer case and I can’t see where the oil is coming from yet. I’ll have to get it up high enough for inspection and pull the fill plug to check the oil level. The boot over the end of the front drive shaft does not appear to be damaged.

Darn it, its not the motor mount either. Today is warmed up into the 50’s so I got out the jack, did a little wood work so I could lift the engine, but when I started lifting it, it was lifting the whole truck. The mount is behind the front differential so it is not visible. I pulled the inner fender and finally got to where I could look at it and it was good.

I looked at the rear mount again, its OK, but then I checked the fluid draining off the bottom of the transfer case and its ATF. I check the dipstick for the transmission and it is dry. So a little more wood work and I jack up the transmission. Thats when I see it, the tail shaft case is cracked all the way around and the transmission is rotated and dropped down. The tail shaft case is only about 3-4" long and mates the transmission to the transfer case. Right now the transfer case looks good but its going to have to come out.

Now to see if I can get a new tail shaft without buying a whole new transmission and if there is no other damage.

I wonder if anyone has ever seen a transmission/PTO spacer fail? It would likely take a heck of an impact to break that.

I got the transfer case out today. It appears that it had been cracking for some time as some of the cracks were not fresh. I also found out that there was supposed to be a shield under the transfer case that was not there. This truck sits pretty high so I wouldn’t think that anything would hit it.

I also found that the front U-joint on the rear driveshaft was NG, the cap bearings are completely gone in two caps. I wonder if the vibration from that could have led to the failure of the adapter.

Is the truck all wheel drive or 4 wheel drive? If it’s 4 wheel drive and left in 4x4 while driving on pavement something will break eventually. Maybe you have reached eventually.

It is an electric 4wd with auto 4wd. In other words the transfer case has 2wd, 4wd hi, 4wd lo and auto 4wd. There is also a neutral in the transfer case for towing. Push button shift.

When a 4wd vehicle is driven on dry pavement in 4wd mode something will eventually break. And if the drive shaft to the front axle was turning it would seem that the truck was in 4wd and eventually truly has arrived.

I know that. The auto 4wd stays in rwd until it detects wheel spin, then a clutch engages to front wheels, and it is quite abrupt when it does, you really feel it. It is not like AWD with a viscous clutch. The owners manual says you can go short distances in 4wd hi on dry pavement but it is not recommended, but 4wd low is for loose surfaces only.

Same setup in my trailblazer, left it in 4 lo pullong the boat out from a slippery launch, was wondering why I could not get over 45. Is your pinion seal leaking?