Broken flexplate

[plydus340]

Drove the duster in the 4th parade the other day. Got lots of compliments. It started making a noise during the parade. Took it to my dads, and he thought it was a rocker needing attention. Pulled the valve covers, and they were fine. I then parked it and asked some buddys what they thought. A couple heard it at the parade and said " check your torque converter bolts". Checked and sure enough, I saw a couple of cracks in it.
I was wondering, Is this due to a mistake of mine? Too much power for stock? I have been stalling it to 1800 when playing with it. You guys tell me what you think. Thanks in advance...

[Locomotion]

I never trusted the stock OEM flexplates, that have openings in the ears, for ANY type of performance application (or "playing"). I have seen and cracked the Mopar Performance HD versions that have solid ears after a lot of racing abuse. But I have been using the B&M plates for years with no problems.

A misalignment between the trans and engine is possible, but rare. In your case, it's probably just fatigue and a replacement should work fine. Unfortunately, I don't know of a "solid ear" flexplate with the small bolts - if you have an OEM type converter.
But B&M has versions that will fit anything if the price is acceptable.

[98Durango5.9]

The same thing happened to my challenger a few weeks ago and when i took it out it crumbled

[jleilich]

throw away that stock flex plate and get the MP one, ive got one on my cuda and its great. that thing is to much of a pain in the ass to replace a hundred times.

[The Dartman]

I had semi circle cracks around two of the four bolts on the HD Mopar piece with the 7/16 bolts.

Chalk it up to too much Mopar Power.... and keep checking them every season...

Dartman

[rustycowl]

my guess is misalignment, which most definitely includes the possibility of a bent flexplate. Most people don't give them a second thought, because they're usually trouble free. But they are easily bent in tear down, or transporting the engine assembly, or installing the engine in the car with the trans already in place.
Spin the engine over and check the runout(frt to back) before you marry it up to the converter. Oh, yeah, don't forget to use blue loctite, AND use a torque wrench on the crank bolts and the converter bolts.

[plydus340]

Thanks for the replys guys. Could you tell me more about misalignment? I must confess I dont know what you mean. They only fit one way, right? Thanks again...

[John Kunkel]

Standard shift bellhousings are align bored at the same time as the engine block so the center holes are in near perfect alignment.
Automatic transmissions are built at a separate plant and there is no guarantee that the center of the trans will be aligned with the block center, so a flex plate is used to couple the two. The thin material of the flexplate will flex and accomodate some misalignment.
If the misalignment is extreme, the exaggerated flexing will eventually cause the flex plate to crack. Higher quality flexplates will take more abuse before cracking.

[ohioDemon]

I broke 2 factory flexplates in my 360 demon. i went and got a b&m and haven't had any problems since

[6 packin]

B&M makes SFI certified plates for many applications were the engine is balanced diff, not wanting to go with the weights on the converter. I Use one on a 360, as for the cracking, I have used a few factory flexplates on 440's with no failure. If every thing was aligned and it wasnt cracked to began with there should be no problem.

[Mister Fiberglass]

it could be an imbalance or a excessive harmonics situation.

[plymsatellite66]

Could anyone describe the sound of a broken flexplate? I have a buddy with a 340 Duster who unfortunately placed it in storage because of what he thinks is either piston skirt slap or main or rod bearings. Not even 100 miles ago he had new main bearings installed after spinning one and the shop said the rods bearings looked fine. We're trying to narrow down the trouble here to get him back on the road, any ideas?

thanks
Corey

[Mister Fiberglass]

never had one do that but I would think....

a clicking, klanking or ticking sound.

[rb77413]

when my flexplate broke, it sounded like a rod knock, I was P.O. till I had to drop the tranny and found out that it wasn't a rod, but the flex plate.

[plydus340]

A metalic ticking sound that varys with the throttle. Thanks for the replys .

[Mister Fiberglass]

just pull the cover and give it a quick eye-ball.