Breaking Flex plates

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This Bad Demon

This Bad Demon

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I replaced a broken flex plate last year sometime in August with one from Advance Auto....I don't drive the car much, but I was drivin it in May shifted round 5200 rpm and come to the stop sign and what do I hear? Ting Ting Ting.....Well that flexplate break also...What causes this? When I go to pull the trans I plan to get the B&M style....Stronger and they say NHRA approved....So I kno that shouldn't break easy...Let me kno....Oh yea 727 small block trans behind a built 318....
 
The nose of the convertor rides in the crank, if the crank of convertor is off much this will happen. Also a bad front pump in a trans too can cause this. '


I do not think it is a weak plate, I think you have a wobble issue, fit the convertor in the crank and see if it is snug, offset etc.

You can mic the convertor and check roundness, but only in a lathe etc can you make sure it is centered>)
 
Usually the cause is running cheaply made junk *** parts. Usually. Buying a flexplate from an auto parts chain ain't the smartest thing in the world, dude. All that stuff comes from China and is so mass produced, I'm surprised they ain't broke outta the box. Also, runnin cheapo chinese made converters like Dayco and the like is an equally bad idea. You want good results, then use good parts.
 
djwhog said:
The nose of the convertor rides in the crank, if the crank of convertor is off much this will happen. Also a bad front pump in a trans too can cause this. '


How can I tell if the front pump is bad?
When I replaced the flexplate the tq fit snug in the pump and didn't have any play
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This Bad Demon said:
How can I tell if the front pump is bad?
When I replaced it the tq fit snug in and didn't have any play...

Buying a flexplate from an auto parts chain ain't the smartest thing in the world, dude...

The one from advance looked better than the one I pulled off the first time....This combo been together for 6 years....They both broke when I speed shift the car!!! I know that B&M piece is alot better....
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StrokerScamp said:
Usually the cause is running cheaply made junk *** parts. Usually. Buying a flexplate from an auto parts chain ain't the smartest thing in the world, dude. All that stuff comes from China and is so mass produced, I'm surprised they ain't broke outta the box. Also, runnin cheapo chinese made converters like Dayco and the like is an equally bad idea. You want good results, then use good parts.
Click to expand...

I know that B&M piece is alot better I plan to get that one.
 
Factory flex plates are junk.I broke 3 and my father broke one.I bought a TCI flex plate and never had to worry about it breaking a flex plate again.TCI only flex plate from now on for me way better design.
 
Mqake sure there is not to much up and down wobble, the pump would need to come out to check wear, and the endplay is checked with a dial indicator.

agree too, use good parts, but I never see stock decnt plates brake unless mega HP @ TQ or balance issues.
 
I had this very same problem. I broke 3 or 4 plates before I checked for the trans bellhousing alignment. Here is the break down. The centerline of the input shaft of the trans is not aligned with the centerline of the crank in the motor. Oddly enough my trans was a small 727 as well. What I did was take my trans to a trans shop and have them take all the internals out of the trans. Then I mounted the case back in the car and mounted a dial indicator to the flywheel flange on the back of the crank (without the flexplate installed). Rotate the motor over by hand and watch the dial indicator for movement. Anything more than a .002 variance is bad. Most people dont realize this can be a problem. My trans guy stated that this problem is more common than most people think. What people regularly do is put a stout full circle flexplate on it and eventually that wears out the thrust bearing in the motor or the bushing in the front pump of the trans. To remedy this problem, Lakewood make offset dowels to relocate the bellhousing. This is a popular thing to do with 4 speed cars that run a aftermarket bell housing. Once I corrected my alignment issues it never broke a stock flexplate again.
 
10-4, they always trans block match when built in the day, sorry I forgot to mention that too:)

Many times after a non OEM trans is installed you need to align it, it is just like a engine balance, line bore etc.
 
The offset dowels are only a little offset and let the bellhousing set flat against motor face. The centerlines stay parallel but the offsets let the trans case move around to align the two centers. I looked in summit catalog and for Lakewood bellhousings they have alignment kit for Ford/Chrysler.
 
moper said:
http://www.robbmcperformance.com/products/dowels.html

I use these. If you're breaking flex plates, you definately have a problem. What exactly was done to the engine to build it up?
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Nothing out the norm...360 heads, a decent cam I thinkin maybe an rv type. When it's runnin people always ask is it a 340.....727 shift kit 2500 stall. Right now the car sits most of the year. The first time it break I had come stateside and I drive it from Danville to Richmond...Went to Wally World, came out catch second come to the stoplight and I hear it start to makin noise. Replace flexplate wit one from Advance Auto...Looked "beefier" than what I pull off. Put it on...Couple months later I come back drive the car....Catch second and come to the stop sign an hear it doin it again......I hope that helps out....Oh yea I shift round 5100 5300 rpm...Nothin to high......
 
That could well be what it is. A lot of times that's what causes it. But to come on here and flat out tell somebody what it is for sure is flippin stupid. Yall don't know any more than the man in the moon what his problem is cause ain't none of yall put a damn mic on it. Bad Demon, I would recommend since you've broken more than one, that you check it yourself or have it done. Yeah, it's a pain in the butt, but sounds like that might be it. No way to diagnose one over the computer for sure. BUT, as per my original recommendation, runnin crap *** auto parts store parts ain't the way to fly. Even after you determine what the problem is, I recommend much better parts than from Autozone or the like. But as said....IF it's out of alignment, the best parts in the world are for naught. I would certainly check it out. I've seen junk aftermarket converters have the bolt pattern welded crooked. Imagine that.It could be several things. No way to know til it's checked out.
 
Factory flexplates dont break under three times that load. There is a problem and "cheap parts store parts" are not it. While I agree PC diagnosing is not really the way to go, in this case, there's not too much else for options for things it could be. He could put on the SFI approved solid versions, and then he'll simply break or wear out something else. The down side is to properly indicate the bell, you will have to disassemble the trans down to the bare case to do it. You must use the same trans case you are running, and you can't indicate with the pump or guts in place...
 
I agree MOPER & Stroker.....especially about the factory plate takin serious abuse without so much as a wrinkle..... I have also bolted 727 small block bells to just about everything small block without so much as a mouse fart..... I have swapped torq Conv from trucks, cabs, and even from after market (TCI) same game.....I believe there is a goodly amount of room for "slop" and exceeding that is tearing up your plates, which tells me, your issue may be more extensive than you think. Like Stroker says get it checked...... we are miles away from what is actually wrong, because most of us are MILES AWAY!!! Hands on & eyes on is what gets the facts.
Back in the day I have done 4000 neutral blasts on stock 727's hangin off 440's 383's 340's 318's, 6 packs, dual quads......NEVER BLEW a 727 or a flex! Those things are tough! Twisted an output shaft all to hell in a 904 hangin off a stock 340 and the plate was intact....the shaft looked like an unevenly unraveled cable, but the plate was true!
Time to visit the tranny guy or maybe the engine guy or maybe both
 
StrokerScamp said:
That could well be what it is. A lot of times that's what causes it. But to come on here and flat out tell somebody what it is for sure is flippin stupid. Yall don't know any more than the man in the moon what his problem is cause ain't none of yall put a damn mic on it. Bad Demon, I would recommend since you've broken more than one, that you check it yourself or have it done. Yeah, it's a pain in the butt, but sounds like that might be it. No way to diagnose one over the computer for sure. BUT, as per my original recommendation, runnin crap *** auto parts store parts ain't the way to fly. Even after you determine what the problem is, I recommend much better parts than from Autozone or the like. But as said....IF it's out of alignment, the best parts in the world are for naught. I would certainly check it out. I've seen junk aftermarket converters have the bolt pattern welded crooked. Imagine that.It could be several things. No way to know til it's checked out.
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Well put. :dontknow:
 
If it's a earlier 318 crank,it might have the smaller pilot hole.
The pilot hole is where the torque converters center hub sits and is held, to stabilize the converter.
If you have too early of a 318 crank, then it is possible that you have a more modern converter snout with an older crank that would need to be opened up to the bigger size.
Measure the crank pilot hole in the back of the crank and then the converter snout(center hub)
Call dynamic transmission and talk to them about what the cause could be, and mention what i just said.
www.dynamicconverters.com phone#(302)454-9203
 
turbodart68 said:
Well put. :dontknow:
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All true and good points without checking to verify 1st, but these are common causes as Moper and others posted.

So throughing a better part yes may work, but that is a cast on the arm for a broken leg.

I do agree it needs to be checked 1st, but I have done 1000s of transmissions in 35 years, and seen many tilted, offset and out of alignment trans to blocks which can cause enough offset to make this failure.

In the old days in a Mopar Bible they even made folks cut every other loop in the plate, and when setup correctly the bigger 8 bolt units rarely broke.

it is all about balance and less flex, no pun intended. :)
 
I preciate all the help....I think I a decent mechanic but I don't know everything so gotta ask u kno.....I KNOW it's better to have hands on but I tryin to gather ideas so when I get stateside to work on the car I have a start....My other question about alignment is this engine and trans been 2gether for about 6 years without a hiccup until the past year or so, can it still get outta alignment? If so how? Trans has neva been out prior to the first one breaking and that was the one the builder put one. The second an the one on it currently is the parts store brand.
 
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