Mopar flexplates breaking like glass

[candeservices]

Are they called flexplates because they are meant to flex?

Yes but, they are supposed to flex axially and Not radially.

 

[alphonso]

Back in '67 I got to talking with the mechanic at the small Chrysler dealership where I was going to school. One of the problems he talked about was the problem of highway patrol cars eating up the crank thrust bearing in the motors. Seems like when they ran them over 110mph the torque converter swelled up and chewed up the thrust bearing. Showed me a block with about an eighth inch of wear on the thrust surface, after eating up the bearing!

 

[Superbowl]

A long shot-- but have you checked the starter gear alignment?

 

[Rickyb]

It looks like a design issue based on the failure and their locations. Flex plate, yes. Unfortunately all the flexing is at the edge (OD) of the mounting hub. the plate is too thin there needs to be thicker then transition to a thinner web gradually. Not going to happen with a stamped plate. They did do a nice job induction hardening the teeth on the OD So they didn’t fu everything. Plate was most likely designed at a supplier and rubber stamped by the Dodge engineer Because it passed some test.. As was mentioned, the OEM engineers are “project managers” that walk around with a timing charts and generally don’t have any design knowledge.

 

[john.k]

Ive never seen a broken one,but I used to fix a lot of flex plates that had a few starter ring teeth chewed out ,as an engine in reasonable condition always stops in the same places .

 

[jim rozen]

late to the party, but inspect the second (upside-down) photo carefully. Almost looks like there are two impact regions near two bolt holes, where the cracks run through those. Photo with the white label visible, suspect regions near the top, near two holes, one hole between the two.

 

[Ox]

Been 35+ yrs since I had an old skewl Chrashler (440/727) apart, but I think that in those days when the term was coined (and it is a Crashler only term AFAIK) I believe that the ring gear was on the Tq convertor? And the "flex plate" was only enough to bolt to both the crank and the T/C. And thus, it had more "flex".

At least that's what I recall?

In the case of this failure, it just gives an impression that the T/C wasn't set back into the pump gear far enough, but I'm not sure what the pump gear on this looks like? Seems like the 48RE (and quite possibly the 727?) uses a "double D" config, but if this was - say - a TH350 (700/4L?) this could be caused by having the center pump gear in upside down, and in that case, the T/C could actually bottom out on the gear, and keep pressure both ways.

This may not be obvious on removal, but it should be apparent on replacement. If the T/C is all the way in when bolted up, you should need to pull it out a bit to mate with the flywheel. If there is tension there upon installation, over time this could happen. (in my theoretical mind - cannot say real world)

But I have no clue what that looks like on a minivan tranny.
But that is what it "looks like" to me.

Yeah, I found a pic of a traditional 440/727 flex plate:




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Think Snow Eh!
Ox

 

[moonlight machine]

Second one in 4 years/50k mi. '11 Dodge Caravan 3.6L. What's going on with this material, does it need to be annealed? Cheap part, but it costs $600 to get to it. OEM MOPAR. This was supposed to be the updated part. I haven't taken a file or center punch to it yet, but it looks like glass....flex plate not flexing, apparently.

Check out the fretting where the torque converter pillars bolt up. That thing has some big time misalignment going on. Bell housing machined on the piss?

 

[Mud]

This may not be obvious on removal, but it should be apparent on replacement. If the T/C is all the way in when bolted up, you should need to pull it out a bit to mate with the flywheel. If there is tension there upon installation, over time this could happen. (in my theoretical mind - cannot say real world)

That should kill the pump long before the flex plate fails.

 

[10 fingers]

For several years I was senior engineer for the largest vendor of torque converter rebuilding components. Had the opportunity to visit many rebuilders throughout the country. It's a whore's market driven by price. Most components are manufactured by the cheapest vendor on earth. Usually in India. Few of the rebuilders have capable machinists and means to inspect what they've built. I assume being on this forum you have a good engine lathe? Chuck on the ground impeller hub. Shim your chuck jaws until the hub has <.0005 TIR. Now check crank pilot TIR and mounting pad TIR. I've lost track of the OEM spec. But consider for about .003 TIR max on pilot and .005 TIR max on pads. If dead serious on buying the the best made, https://www.coanracing.com/converters.html

 

[Ox]

That should kill the pump long before the flex plate fails.

I would think so too.
But it still looks like Z axis thrust / clearance....

AND - a misalignment would seem to take the pump out as well, so ...
Maybe quicker...
Or at least blow out the front seal before the plate cracks?

A bottomed T/C would not want to take out the pump bush/seal nearly as bad as a mis-alignment would.

AND, if maybe the neck on this T/C set-up went through the gear, and then maybe bottomed on sumpthing a bit heavier - like input shaft where the pressure went into a thrust bearing?

Edit - added
Not sure why this software doesn't have a field for "reason for edit?"


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Think Snow Eh!
Ox

 

[UptownSport]

.... If the engine and transmission are not perfectly aligned the plate will crack at those positions.

And @eKretz are correct.

Had a 318 w/ a 904, had to buy offset dowels to align and keep the 'Drive Plate' from cracking.

Runout check s part of every clutch job, did they just make slushbox tolerance tighter?

 

[tomjelly]

Yeah that other post from 5/21/19 is mine too, the first broken one. My guess is misaligned engine to trans from the factory, there is a much later year tsb (2019 I think) that mentioned something about that. Unfortunately I can only drop this thing off at the shop and pick it up and wouldn't have a way to measure that alignment to the degree of accuracy that would help, I would do it myself and figure out a way if I had a lift here but I don't. I think this car will get sold before the next 4 year breakage interval arrives, at least that will be another incentive to do so! The dealer managed to not tighten the cam chain guide bolts (among other things) when replacing a cylinder head under warranty shortly after we purchased it. 100k later I discovered they fell out. I was replacing all the valve rockers as one had seized. I couldn't get the cam timing right because of mystery chain slack and had to take off the whole front of the motor to reattach the chain guide, so I stick with one particular independent shop for the stuff I don't want to deal with. I was lucky that chain slack didn't destroy the engine.

 

[Ox]

How did you figger out the amount and direction of mis-alignment on the 904?

A dial indicator on the input shaft - and reading on the pilot bore (more likely the OD I guess) in the crank?
Leave the pan off so that you can spin the input shaft assy?

Not that the input shaft is that solid, but prolly gits you in the ballpark?


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Think Snow Eh!
Ox

 

[john.k]

When you buy a spare part Allison flex plate ,its blank on the crank bolt circle ......you drill your own to suit the motor.......had one where the mechanic had reversed the old plate over the new one to drill the holes......uh -oh......the bolt circle isnt regular spaced ,so the reverse pattern wont fit .....buy another $100 plate......or elongate the holes until they fit.

 

[DrHook]

Indicate the crank flange face.

 

[UptownSport]

How did you figger out the amount and direction of mis-alignment on the 904?

A dial indicator on the input shaft - and reading on the pilot bore (more likely the OD I guess) in the crank?
Leave the pan off so that you can spin the input shaft assy?

Not that the input shaft is that solid, but prolly gits you in the ballpark?


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Think Snow Eh!
Ox

Indicate around the, what, 'reaction shaft' on front pump housing, or remove the front pump housing and use a dial indicator in the opening

You want to be very careful @Ox , that you don't get confused and indicate the rear pump housing

 

[eKretz]

How did you figger out the amount and direction of mis-alignment on the 904?

A dial indicator on the input shaft - and reading on the pilot bore (more likely the OD I guess) in the crank?
Leave the pan off so that you can spin the input shaft assy?

Not that the input shaft is that solid, but prolly gits you in the ballpark?


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Think Snow Eh!
Ox

Pilot or OD *and* the rear face of the crank, I think.

 

[Ox]

Pilot or OD *and* the rear face of the crank, I think.

Something has to turn.



Sport:

So you put your indicator on the crankshaft then?
Oh heck, what am I thinkin' - you just need to mag it to the fly ... uh - flexplate and then inch that around.
WAY easier than I was envisioning!
Of course all you need is an empty tranny and the pump housing to doo that...
Well, that would be way easier on this tranny with the ring gear on the flexplate than on your 904 - to "inch" it around that is.

When I worked in the tranny shop in 1986, my cousin sold a trans brake set-up.
(seems like maybe ATI, ATS, or sumpthing like that?)
And so I wouldn't be surprised that a few slip and slides may have went behind a Chrashler motor here and there, but I don't think that any of those 2 speed miracles that went out our door had iron cases nor rear pumps.
I've never [knowingly] even seen one of those animals to date.
(But there was a 345 W motor on a stand upstairs - so that was cool! - not ours tho - cold storage)


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Think Snow Eh!
Ox

 

[eKretz]

Something has to turn.



Sport:

So you put your indicator on the crankshaft then?
Oh heck, what am I thinkin' - you just need to mag it to the fly ... uh - flexplate and then inch that around.
WAY easier than I was envisioning!
Of course all you need is an empty tranny and the pump housing to doo that...
Well, that would be way easier on this tranny with the ring gear on the flexplate than on your 904 - to "inch" it around that is.

When I worked in the tranny shop in 1986, my cousin sold a trans brake set-up.
(seems like maybe ATI, ATS, or sumpthing like that?)
And so I wouldn't be surprised that a few slip and slides may have went behind a Chrashler motor here and there, but I don't think that any of those 2 speed miracles that went out our door had iron cases nor rear pumps.
I've never [knowingly] even seen one of those animals to date.
(But there was a 345 W motor on a stand upstairs - so that was cool! - not ours tho - cold storage)


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Think Snow Eh!
Ox

Yeah, still need to rotate the crank or the input shaft. Just sayin': it'd be a good Idea to check angular alignment too. Could be close to centered but tilted.