Alright this is a little time sensitive so I just threw it in here. But back in September I replaced my transmission. End of December my flexplate broke. I took it to a shop and they replaced the flexplate after I asked them to figure out what happened. They had my car for 2 weeks. I guess they had problems with getting the flexplate. I broke another flexplate this week and I’m arguing with the shop about who takes blame. They tell me the reason it broke was because I didn’t have dowel pins. And they told me to come back to install them. I thought it was bs why put everything back together just tell tell me there was no dowel pins. Whatever. Now here’s my issue. There was no dowel pins when I took the transmission apart I can not find a part number. Or a single diagram that says anything about dowel pins. Even if there was can missing them really break a flex plate like it did?

 

It's not a dowel pin on the crankshaft, it's an ALIGNMENT PIN because it installs in a specific orientation on the bolt pattern of the crank. If not the crank position sensor reads the outer part of the ring wrong.

Not why you're shattering the welded inner ring on the flex plate, they're probably not installing the backer plate / reinforcement plate (part 1 on the diagram).

Or they don't have the correct pilot bushing on the crankshaft, with the 6MT bushing there's nothing to center the flex plate/flywheel. It MUST use the 5AT one. If it's the same engine it probably has the correct pilot bushing but it should definitely be checked.

It's also possible they didn't actually torque the bolts but rather just impact wrenches the ever living F out of it and damaged the metal, not likely but it's possible.