Breaking Flex plates

[pettybludart]

It can come out of alignment if the bellhousing bolts become loose from vibration.After you get it dialed in,get yourself a S.F.I approved flexplate.They,re alot thicker and you can get one from any performance dealer.Good luck,I,ve been there!LOL.
View attachment Racing the 66 Dart 036.jpg

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This damage was caused by a bent driveshaft.

 

[JGC403]

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.

I know the thread is kind of old, but I had a question. How do you get the dial indicator mounted to the flywheel flange on the back of the crank perfectly centered on the crank?

 

[moper]

I know the thread is kind of old, but I had a question. How do you get the dial indicator mounted to the flywheel flange on the back of the crank perfectly centered on the crank?

It doesnt need to be centered. It needs to be able to be read as the engine is rotated and the plunger of the dial indicator has to ride on the machined ID surface of the pump bore on an auto, or the input bearing retainer bore on a bellhousing. As the flywheel or flexplate or crank hub rotate, the relationship between the spot on the surface it's stuck to and the sides of the bore will not change unless the bore is not centered on the rotational centerline.

 

[JGC403]

It doesnt need to be centered. It needs to be able to be read as the engine is rotated and the plunger of the dial indicator has to ride on the machined ID surface of the pump bore on an auto, or the input bearing retainer bore on a bellhousing. As the flywheel or flexplate or crank hub rotate, the relationship between the spot on the surface it's stuck to and the sides of the bore will not change unless the bore is not centered on the rotational centerline.

I think I know what you mean. Just to be sure though does anyone have a picture.

 

[mopardude318]

what are you guys using for sfi flexplates?

 

[turbodart68]

Here are some photos of the process. I use B&M myself for SFI flexplates.

 

[JGC403]

Thanks