Flywheel Breakage

[mitmur1998]

Hello all. I have a 1990 toyota corolla with a 4afe motor and automatic transmission. I have broken three flywheels. They always break in the center. The starter teeth and the flywheel teeth look ok. So I am assuming no starter problems. Anyone have any idea what might be causing this. It usually takes about 30 days to break after I replace it. Any help will be greatly appreciated as It is getting old pulling that transmission.

[Flashmn]

uneven mounting surface, badly torqued bolts... those are few that might cause it.

[toyomoho]

Did this breakage just start to happen or did you change out (repair) the transmission or engine? Is this the original trans and engine setup?

I suggest you find a very shop manual that details the installation of the torque converter to the flex plate, and trans to engine block. There are specific clearances and torque settings that must be used or problems will occur. If you cannot find details for the make of car, find a similar engine/transmission combination and get this info. A Google search on “flex plate cracking” will turn up a number of hits.

Some issues are: don’t buy cheap flex plates of low quality, worn thrust bearing (to much crank end play), improper torque of fasteners, bad engine or transmission mounts. The transmission may not be aligned correctly with the engine block (installs at an angle).

The flex plate is flexing too much. The result is stress around the center area that bolts to the engine, which is leading to cracking. Imagine if the transmission were grossly misaligned with the engine. The flex plate is bolted the crankshaft and torque converter, the torque converter slides onto the transmission input shaft. The engine is rotating, the flex plate is going to flex (bend) as the crank goes around. The weakest point is where the plate bolts to the engine. Eventually the metal fatigues and starts to crack, then fail.

[mitmur1998]

I had the engine put in the car about 7 years ago. I put a ton of miles on it before I broke the first flex plate. Do you think bad motor mounts could cause the breakage? I thought about that and then I thought the motor and transmission are locked together so if one was moving then the other was moving with it. Its just strange that the first one broke and so did the next two that I put in. I just didnt feel it was the installation. I figured whatever broke the first one probably broke the next two. I could be wrong, but just what I was thinking.