What could cause the flywheel to crack??

[78 mudder]

Hi I have a 1978 chevy pickup 4wd on a 82 GMC 1500 frame with a 400 engine and I had a turbo 350 with a 203 transfercase. The transfer case blew on me so I replaced it with a turbo 400 with a np208 transfercase and I drove it for a month and everything worked great no problems! But I took the truck mudding and after I noticed a clinging noise and my fly wheel is cracked. I used the torque coverter from the turbo350 and I'm not sure what could cause this?? Note: lifted with 6inch suspension 2 inch body 35s with 2inch loward transmission Braket. Any help would be assume cause I don't want to just replace it and have it happen again!

 

[DoubleDingo]

Technically it's a flex plate. Flywheels are for manual transmissions. But good question for why the flex plate would crack unless it was fatigued and the mudding excursion caused it to finally fail.

 

[78 mudder]

Yes I ment flex plate. But I'm not sure if it's just the flexplate that went bad or if it had to do with the torque converter and transmission set up or something else? I also am missing the bar that goes from the transfercase up to the transmission to help stabilize it if that has anything to do with it.

 

[chengny]

The thread title asks "what would cause a flexplate to crack"?

Almost always misalignment. Check your (new) flexplate to T/C pad clearances. Rotate both the engine and T/C at the same time and check 180 degrees apart (or as close to that as you can). With the flywheel/flexplate cover off, check at the point where the bellhousing and block meet.

Make sure the faces of the engine block and bellhousing are smooth and that your locating dowels are in place.

Lastly, check both the crankshaft and transmisson input for runout also be sure neither has excessive endplay.

Despite the name, flexplates can tolerate very little flexing due to mis-alignment.

That stiffener that goes from the transfer case to the bell housing is good to have, but not having it for one trip in the mud shouldn't cause a cracked flex. Think about it, you didn't have one before - how long did the last setup last?

 

[78 mudder]

the last set up with the turbo 350 and the 203 had that connecting peice i would switch it over but the 208 has different mounting holes so i need to either find one or mess with my old one to make it fit. im going to try to get the flex plate off soon when i have time and i will check all the mounting and how everything fits. thanks alot!

 

[crazy4offroad]

Also important to consider is what size tires you're running and with what axle gears? Too big of tires with the wrong gears can cause a lot of stress.

 

[78 mudder]

I'm runnin 35s with 3:07 gears yeah I know their low but it's my daily driver so it helps out on gas milage haha

 

[78 mudder]

But I'm probably going to put a heavier duty flexplate in and after I check everything out and figure out what's wrong with it. It's a bitch to drop the trans and transfercase so you think I can but longer bolts in and just try to move the trans back enough to pull the plate?

 

[crazy4offroad]

Yup, another member had mentioned this a few months ago. Maybe some allthread.