I'm almost positive the flex plate in my '72 340 Duster has cracked. There's a heavy knock when the tranny is in park, or neutral. In drive, reverse, or while driving, it makes not a sound. I want to replace with the B&M round flex plate...Good idea? Anyone ever had to deal with this? I understand Chrysler flex plates were notorious for cracking between the punched out slots. This is the original plate with the car, as I am the second owner, from my father. I'm finally ready to tackle the job, Being 48, my days underneath a vehicle are few, and far between. So my local mechanic will do the job for $400.00. But is the B&M plate $81.00 a good replacement?

 

Yes it is fine, good investment. I would check and make sure the bolts on the converter are tight first. As the flex plate will move slightly when going to different gears Maybe ????

 

Make sure you get "the correct one" if you do this. Many of the BM ones are special, weighted, meant for example, using a neutral balance converter behind an LA 360, etc.

Not knowing how hard you drive or the HP level, you might be overthinking this. I'm not sure I'd agree that "notorious" is the word. I've got several factory flexplates out of SB Mopars in the garage, and not one of them shows any sign of cracking.