2000 Tahoe flywheel bolts sheared off. How'd that happen?

[Diesel6point6]

Hi guys, wondering if you could shed some light on how this might have happened because I have no idea, and I'm really curious. I bought a tahoe with a suspected bad transmission. I just pulled the engine and trans together and went to take out the flywheel bolts and was shocked to see there weren't any. Got the tranny and engine separated and could clearly see the bolts had all been sheared off, a lot if carnage was done to the flywheel itself, the rear cover, and the oil pan. What could have caused that? Engine was running really smooth before pulling.

 

[Diesel6point6]

Just realized I put this in the wrong section. D'oh! Mods, can you please move or delete and ill repost in the correct one? My bad.

 

[Scottydoggs]

my first thoughts are someone drove it like they stole it. aka beat the living crap out of it one day. and came home on a tow truck, then sold it as is, "has a bad tranny" now you get to fix it.....

 

[nonickatall]

I guess something blocked the transmission while engine was running at high revolution. Probably something in the transmission or in the transfer case stuck.

Can your turn the input shaft of the transmission?

I don't think that it's possible to do that damage, by shifting into P or R while driving.

 

[strutaeng]

Post some photos so we can have a better idea and do some wise speculation...

 

[Mudsport96]

Could be a couple things.
1. Hard part internal transmission failure Locked the pump up and stopped the converter.
2. Reverse drop/neutral drop shock loaded the flexplate.
3. Bolts started to work loose then the flexplate beat them to death.
4. Gremlins.

 

[nonickatall]

Could be a couple things.
1. Hard part internal transmission failure Locked the pump up and stopped the converter.
2. Reverse drop/neutral drop shock loaded the flexplate.
3. Bolts started to work loose then the flexplate beat them to death.
4. Gremlins.

I guess gremlins is the most likely issue...

 

[Diesel6point6]

I guess something blocked the transmission while engine was running at high revolution. Probably something in the transmission or in the transfer case stuck.

Can your turn the input shaft of the transmission?

I don't think that it's possible to do that damage, by shifting into P or R while driving.

Yes, input shaft spins freely. A bit squeaky, but freely nonetheless.

Post some photos so we can have a better idea and do some wise speculation...

I've attached some photos of the carnage. First of the bolts sheared off in the torque converter (I should have been more clear in my original post that it was these, I thought later it might cause some confusion and some might think it was the bolts attaching the flexplate to the block, those were still intact), 2nd is the flexplate, 3rd is one of the bolts I found inside the bellhousing, 4th is of the rear of the engine (sort of hard with it on the engine stand)

 

[strutaeng]

I guess one possibility is the flexplate bolts (somehow) worked themselves loose, and they kept driving until the flexplate bolts hit something and flexplate fell off? I don't even know if that's possible?

What are you going to do to the truck? I would be checking engine front-to-back endplay just to make sure you don't have a destroyed thrust bearing.

IDK what to even say about the transmission, as far as if damage was a possibility. Probably front end play as well. @NickTransmissions may offer some advice.

What did the previous owner tell you about the truck? Is that even known?

 

[Diesel6point6]

I guess one possibility is the flexplate bolts (somehow) worked themselves loose, and they kept driving until the flexplate bolts hit something and flexplate fell off? I don't even know if that's possible?

What are you going to do to the truck? I would be checking engine front-to-back endplay just to make sure you don't have a destroyed thrust bearing.

IDK what to even say about the transmission, as far as if damage was a possibility. Probably front end play as well. @NickTransmissions may offer some advice.

What did the previous owner tell you about the truck? Is that even known?

Yeah I read some threads that mentioned sometimes one bolt backs loose from the torque converter, which then in turn gets everything out of whack and it eventually causes carnage if it keeps getting driven. My best guess is this is what happened to this one.

I'm going to swap it into my S10. This is the 3rd one I bought with that purpose, the first 2 I didn't have the heart to pull the engines out and still drive to this day haha! I guess you can say I have a love for these SUVs. But would the engine sound as good as it did before pulling if there was a destroyed thrust bearing? My knowledge in this department is very very limited.

The previous owner said the transmission was bad. Said he was driving it one day, heard a clunk, then no movement. Which makes sense, if the torque converter fully separated from the flexplate that would make the vehicle immovable. I have my suspicion if the tranny is in fact still good though? Again, my knowledge is very limited so I could be way off base here, but the torque converter bolts separating from the flexplate would exhibit behaviors of a bad transmission (just revs), but that could be because there was just nothing attaching the engine to the torque converter at that point, but the internals of the transmission are still good? Idk lol.

 

[strutaeng]

Yeah I read some threads that mentioned sometimes one bolt backs loose from the torque converter, which then in turn gets everything out of whack and it eventually causes carnage if it keeps getting driven. My best guess is this is what happened to this one.

I'm going to swap it into my S10. This is the 3rd one I bought with that purpose, the first 2 I didn't have the heart to pull the engines out and still drive to this day haha! I guess you can say I have a love for these SUVs. But would the engine sound as good as it did before pulling if there was a destroyed thrust bearing? My knowledge in this department is very very limited.

The previous owner said the transmission was bad. Said he was driving it one day, heard a clunk, then no movement. Which makes sense, if the torque converter fully separated from the flexplate that would make the vehicle immovable. I have my suspicion if the tranny is in fact still good though? Again, my knowledge is very limited so I could be way off base here, but the torque converter bolts separating from the flexplate would exhibit behaviors of a bad transmission (just revs), but that could be because there was just nothing attaching the engine to the torque converter at that point, but the internals of the transmission are still good? Idk lol.

You buy the GMT800 SUVs to do an "LS swap on another vehicle" and then just keep driving them because you love them so much?!

Hell yeah, my type of guy! Give this a man a cookie!

I always fret when I see otherwise just a running GMT800 getting parted out just for the engine, especially when it's getting swapped in a POS vehicle. Not saying your S10 is a POS, just a general statement, if you know what I mean.

So I was suggesting checking your thrust because if some have excessive end-play, that can wipe out your transmission pump, as they are only supposed to have a specified amount of endplay. It's just installing a dial indicator on the front crankshaft and pushing the flexplate to measure it. Takes like 5 minutes.

At this point, it almost seems like all you had was the flexplate falling off... maybe you are lucky here... IDK

 

[Diesel6point6]

You buy the GMT800 SUVs to do an "LS swap on another vehicle" and then just keep driving them because you love them so much?!

Hell yeah, my type of guy! Give this a man a cookie!

I always fret when I see otherwise just a running GMT800 getting parted out just for the engine, especially when it's getting swapped in a POS vehicle. Not saying your S10 is a POS, just age general statement, if you know what I mean.

So I was suggesting checking your thrust because if some have excessive end-play, that can wipe out your transmission pump, as they are only supposed to have a specified amount of endplay. It's just installing a dual indicator on the front crankshaft and pushing the flexplate to measure it. Takes like 5 minutes.

At this point, it almost seems like all you had was the flexplate falling off... maybe you are lucky here... IDK

Haha yes sir! First was an 03 Denali. Runs so good it's now my daily driver. Second was an 04 Tahoe that suffered a deer hit. Decided to rebuild the front end and keep it lol. This current one was in really bad shape exterior wise so I decided it wasn't worth repairing.

I completely get what you mean. It breaks my heart as well to see perfectly good GMT800s gutted just for the engine. And let's be honest, many of the swaps don't see completion because the owner bit off more then they could chew. See it all the time.

Got ya, thank you for the clarification on the thrust. I'm learning so much as I go and I absolutely love it.

 

[buckwild27]

I have seen a handful of vehicles where the flexplate bolts come loose and fall out or sheer off.

 

[fredcook]

Maybe it's just the pics, but those bolts look pretty rusted. My first thought is the bolts were over torqued and eventually failed. Also, again maybe just the images, but it looks like at least two of the bolts broke inside the surface of the converter. That's more a sign breakage under pressure (over tightened) versus sheering off.

I've been though a couple of driveline/rear end lockups. In both cases, it was the transmissions that broke apart and took the hit. One was a beefed up automatic (TH400) that completely disintegrated internally. The other, a T56 manual, broke apart enough to also lock up, which lead to a yoke snapping off. In neither of these cases were there any signs of stress at the flywheel connections to the torque converter or clutch.