General A727 Potential R&R questions/suggestions.

[Big_John]

So I presume, to get a new flexplate.
you need to measure the new converter bolt circle size and go from there?

You can always do something like this.. It fits everything.

JEGS 601085: Heavy-Duty SFI Flexplate for Mopar, Chrysler Small Block and Big Block [With TF727 Transmission] - JEGS

I think the bolt patterns are 10" and 11" if you want to try to find a stock style.

One thing... Double check your flex plate against the convertor just to be sure before you buy a flex plate... and remember one bolt of the 4 is offset.

 

[Sir Dodge alot]

You can always do something like this.. It fits everything.

JEGS 601085: Heavy-Duty SFI Flexplate for Mopar, Chrysler Small Block and Big Block [With TF727 Transmission] - JEGS

I think the bolt patterns are 10" and 11" if you want to try to find a stock style.

One thing... Double check your flex plate against the convertor just to be sure before you buy a flex plate... and remember one bolt of the 4 is offset.

Yes I have not checked yet, consensus I've heard around is 11.75 stock converter.

Thanks for the link Sir!

Edit: I just looked at the specs on the new Torque converter, it's a 10 inch bolt circle, I'll look at how you measure it though.

 

[Sir Dodge alot]

Just measured the New Torque converter with two measuring methods.

From bolt to across bolt center is 10 inches.

The other method is center of the Torque converter to the bolt hole is 5 inches, multiply that by 2.
5X2= 10

the flexplate is a factory 6 bolt pattern.

I think I have enough information to know what flexplate to get.

6 bolt, 10 inch bolt circle flex plate.

The other information I gathered was, avoid non USA made flexplates.

SFI rated flexplates are not required but a little bit more of a "well made" product doesn't seem like a bad idea.

 

[Sir Dodge alot]

Ok so I just did some research on the flexplates, if the New and the old Torque converter bolt circles are the same, I should be able to use the factory flexplates.
If I line up the bolt holes?

there's a 3 month back order for Jegs, I'll try summit or some other sources.

 

[Big_John]

Ok so I just did some research on the flexplates, if the New and the old Torque converter bolt circles are the same, I should be able to use the factory flexplates.

That's correct and why I said to check the bolt circle on your old convertor. It's possible that it's the same bolt pattern, but I don't think it will be.... Just don't take my word for it.

I just would hate to see you bolt up the transmission and then find out it's the wrong flexplate.

 

[Sir Dodge alot]

Question if anybody is able to answer:

The Flexplate has 4 bolt holes to the torque converter, but what is the small hole between the 5/16 bolts holes.

Index hole to line up the converter to flexplate I assume?
What is it exactly for?
Can't exactly find any information on it.

Thanks.

 

[Sir Dodge alot]

@Big_John Thanks for the link to the Flexplate a while back, present day, I managed to get a supposedly SFI rated Flexplate and got the Trans & the Torque converter mounted in place with the somewhat stock looking Flexplate, with the Torque converter fully seated back to a depth of
inch and a quarter.

Thanks again @Big_John

 

[Sir Dodge alot]

I wish the transmission would just install it's self at this point! XD

 

[fury fan]

FWIW, I would not use that new flexplate. Those half-moon cutouts look to have sharp corners, and sharp corners make stress concentrations, and that's where things break.
Whoever did the CAD design for that needs a little what-for behind the woodshed. Along with every engineer afterward that didn't raise a flag about it.

Is it going to break? I don't know. But it's a flexplate, and they must endure a workload 99% of us don't have a good concept of. (I consider myself in the 99%)
I watched GM go thru 6-8 different flexplate designs in about 4 years for their V8 Duramax diesel. The size/shape of the cutouts were critical, and none of them had sharp corners, either.

Also - you are not intending to install the trans with the flexplate on the converter, right?

 

[Sir Dodge alot]

FWIW, I would not use that new flexplate. Those half-moon cutouts look to have sharp corners, and sharp corners make stress concentrations, and that's where things break.
Whoever did the CAD design for that needs a little what-for behind the woodshed. Along with every engineer afterward that didn't raise a flag about it.

Is it going to break? I don't know. But it's a flexplate, and they must endure a workload 99% of us don't have a good concept of. (I consider myself in the 99%)
I watched GM go thru 6-8 different flexplate designs in about 4 years for their V8 Duramax diesel. The size/shape of the cutouts were critical, and none of them had sharp corners, either.

Also - you are not intending to install the trans with the flexplate on the converter, right?

Yes sir, I was just mocking the Flexplate into place seeing whether the bolt holes would line up, no issue there.

The Flexplate will be bolted to the crank first, then bring the trans with the TC and cinch up the engine/trans together.

Thanks for the Flexplate once over, if the half moon cutouts are bad, then I'll take original Flexplate off of the crank and see if that will bolt up to the new TC.

Seems like the GM designers needs an earful from the community & re-evaluate the Flexplate design!
Flexplate design with planned obsolescence in mind? Hm, I wonder!

 

[fury fan]

Seems like the GM designers needs an earful from the community & re-evaluate the Flexplate design!
Flexplate design with planned obsolescence in mind? Hm, I wonder!

No, we were breaking flexplates during transmission testing, and every MY the engine torque output was increasing, and we'd find last year's flexplate wouldn't survive.
So they'd scramble to try different shapes - circle, ovals, kidney-bean shapes.
The GM engineers were trying to make a durable part.

 

[Sir Dodge alot]

No, we were breaking flexplates during transmission testing, and every MY the engine torque output was increasing, and we'd find last year's flexplate wouldn't survive.
So they'd scramble to try different shapes - circle, ovals, kidney-bean shapes.
The GM engineers were trying to make a durable part.

That's a tall order considering Diesels are torque monsters, was GM diesel trucks with the Flexplate that kept failing recalled/remedied in the end?

 

[65CopCar]

I don't like that flexplate either. What's with the double drilled bolt for the crank?

Do you have 5/16 or 7/16 bolts? If 7/16 I can send you an expired Mopar SFI one. Perfectly good just not legal for racing anymore.

 

[Sir Dodge alot]

I don't like that flexplate either. What's with the double drilled bolt for the crank?

Do you have 5/16 or 7/16 bolts? If 7/16 I can send you an expired Mopar SFI one. Perfectly good just not legal for racing anymore.

Hi there, the Flexplate bolts are indeed 5/16.
Thanks for the offer though, But really I'm flat broke this month, I may take you up on that next month or so. Thanks.

I think the double drilled hole for the crank bolt holes are to accommodate different size TC to crank interface?

To be honest, I think drag strips would not let me race, not just because the expired SFI Flexplate, but just because my barge is too slow. Lol
But if I had to guess, it'll probably do 14 seconds flat or 14.35? I digress.

 

[fury fan]

That's a tall order considering Diesels are torque monsters, was GM diesel trucks with the Flexplate that kept failing recalled/remedied in the end?

No, this was in pre-production durability testing, AFAIK no bad designs ever made production.
What was durable for 1 MY of production might not be good enough for the next year. 2010 brought a ~50hp increase, and IIRC that's where the trouble started.
We started cracking them, and they sent a new design to see if it would survive. Sometimes yes, sometimes no.
Then sometimes they'd survive to teh 1st 1000-hour transmission inspection, but the flexplate would fail before we'd get to the next inspection at 2000 hours.
I don't remember all those details, except that the transmission would generally outlast 2 engines and 3-4 turbos and sets of injectors.
We got the Duramax weak parts replacement down to a science.

I do pity the guy that takes an older flexplate and installs with a newer engine, saying 'it'll bolt in, it'll work jess fine.'

 

[Sir Dodge alot]

No, this was in pre-production durability testing, AFAIK no bad designs ever made production.
What was durable for 1 MY of production might not be good enough for the next year. 2010 brought a ~50hp increase, and IIRC that's where the trouble started.
We started cracking them, and they sent a new design to see if it would survive. Sometimes yes, sometimes no.
Then sometimes they'd survive to teh 1st 1000-hour transmission inspection, but the flexplate would fail before we'd get to the next inspection at 2000 hours.
I don't remember all those details, except that the transmission would generally outlast 2 engines and 3-4 turbos and sets of injectors.
We got the Duramax weak parts replacement down to a science.

I do pity the guy that takes an older flexplate and installs with a newer engine, saying 'it'll bolt in, it'll work jess fine.'

I thought about it for some time, but a weak point in the drivetrain like a Flexplate doesn't sound bad, considering a broken Flexplate is easily replaced, compared to an engine/transmission etc.

 

[fury fan]

I thought about it for some time, but a weak point in the drivetrain like a Flexplate doesn't sound bad, considering a broken Flexplate is easily replaced, compared to an engine/transmission etc.

I have seen diesel-engine torsionals break a transmission, but it always happened to a component that was loaded when torque converter lockup clutches were applied, and the damper springs on that clutch were not effective to dampen the torsionals. And when it happened it was always traced to an engine that had injector issues, making the engine more torsionally active. FWIW, it always happened to a Brand X, 26ft box truck, with a particular engine, whose transmisison calibration was limited to 5 out of 6 speeds. 6th gear was locked out due to a resonance frequency in the engine's rear adapter housing, which would get excited in 6th gear at highway speeds. So the engine adapter housing was saved, but a particular planetary carrier in the transmission was unknowingly placed next in line to take the hit.

95% of our old cars still have an AT with out a lockup converter - and the fluid in the converter will absorb any torsionals from the engine.

So - the flexplate in your car should last forever if it's installed properly. There's no need to put one in to act as a fuse.

 

[Sir Dodge alot]

I have seen diesel-engine torsionals break a transmission, but it always happened to a component that was loaded when torque converter lockup clutches were applied, and the damper springs on that clutch were not effective to dampen the torsionals. And when it happened it was always traced to an engine that had injector issues, making the engine more torsionally active. FWIW, it always happened to a Brand X, 26ft box truck, with a particular engine, whose transmisison calibration was limited to 5 out of 6 speeds. 6th gear was locked out due to a resonance frequency in the engine's rear adapter housing, which would get excited in 6th gear at highway speeds. So the engine adapter housing was saved, but a particular planetary carrier in the transmission was unknowingly placed next in line to take the hit.

95% of our old cars still have an AT with out a lockup converter - and the fluid in the converter will absorb any torsionals from the engine.

So - the flexplate in your car should last forever if it's installed properly. There's no need to put one in to act as a fuse.

Great write up sir!
Didn't think the TC and the fluid inside could act like a shock absorber, the more you know.

In the meantime, I suppose I'll wrestle the original Flexplate off of the crank and see if I can use that instead of the new Flexplate, if so that'll be great, just hoping the original Flexplate to TC bolt holes will line up.

 

[Sir Dodge alot]

As I was looking over the condition & the linkages and the block, made a discovery that I didn't need right now.

I suppose an engine removal and metal stitching repair & or nickel rod welding is in my near future!

What are the odds eh?
pulls transmission for a rebuild, ends up needing an engine repair/replacement also.

There's the occasional cold snap here in Texas from time to time and I've been diligent in draining coolant/water from the radiator when that happens, I came up short this year and didn't even remove the water jacket drain petcock from the engine block.
My costly mistake.

I guess the car being garage kept, wouldn't save the block from the cold snaps clutches.

 

[65CopCar]

Ouch!