Flex plate cracked

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cudajim

cudajim

cudajim
Joined
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I'm running a 225 super slant six with a 904 automatic. I noticed a slight tick while idling and has recently become louder. It sounded like it was coming from the transmission so I decided to have a look this weekend. I took the inspection plate off the trans and found the flex plate cracked at all 4 bolt holes on the torque converter. I've never had this problem with any other Mopars so I have to wonder what caused it and how to prevent it in the future. I also need another flex plate which I believe is a 10" bolt pattern.
 
Offhand I'd guess something is bent/ worn/ damaged. Bell misalignment, worn converter ??? sounds like time to do some serious inspection
 
I have seen them cracked. replaced them on peoples cars an i never had any come back. Yours could have been through some heavy neutral drops in life with an aggressive driver. Like most of us.
 
It was in good shape when installed a year ago. I never did neutral drops or anything else to abuse it. I'll be pulling the trans out this week to have a look. Can't drive it in the meantime so I have to fix it.
 
My guess would be either metal fatigue from long age or an after-market one with inferior metal. I had a cracked flex-plate in my 2002 3.8L Mopar. It had cracked all around the crank bolts and rotated 20 deg, plus radial cracks. That seems to be a common problem in the 3.3/3.8L V-6's. The cracks looked like brittle metal. I recall that both the original and dealer replacement were stamped "Canada". There are after-market racing ones for SB & BB. I don't know if they fit a slant (same crank holes?).
 
Drill the ends of the cracks , J.B. weld it and put it back on. Why not get your money out of it. LOL
 
I have had this happen when I ran automatics behind my big blocks.I quit using stock flex plates a long time ago.But with a slant a stock flex plate should be OK.I would replace it.
 
Oldmanmopar said:
Drill the ends of the cracks , J.B. weld it and put it back on. Why not get your money out of it.
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Even I am not that cheap. Now my Dad would have done that, and when his scotch-tape fix failed he would say "can't fix a car" and buy another used car. He would have also rounded off the bolts by using an adjustable wrench rather than buying the right tools. There is "smart cheap" and then my relatives.
 
Cudajim, what year engine/trans/car? If it is a 67 down trans, and a 68 up engine, was a crank adapter bushing used?
 
BillGrissom said:
Even I am not that cheap. Now my Dad would have done that, and when his scotch-tape fix failed he would say "can't fix a car" and buy another used car. He would have also rounded off the bolts by using an adjustable wrench rather than buying the right tools. There is "smart cheap" and then my relatives.
Click to expand...

That was my dad. Coke cans and hose clamps for the exhaust fix. That's where I learnt-em-all
 
cudajim said:
It's a 68 engine & trans. The torque converter fits the crank too (I measured it last night).
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Good, it was just a thought, as I have seen quite a few engine swaps, where this was over looked. One other thought. You do have the proper nuetral balance converter, right? A cast crank small block 904 converter will fit, but will be out of balance for a slant six.
 
Be sure to take a look at the aligning hub on the front of the converter and make sure it fits the crankshaft.
 
Sometimes because of production tolerances the crank centerline and bellhousing centerline are offset enough to cause the flexplate to crack. Mopar Performance used to sell offset dowels to correct the problem. If it is more than .008 it needs corrected. On an automatic you have to gut the trans case ,rig a dial indicator to the crank so that it indicates off the pump housing bore to find how much it is off and which direction to put the offset dowels.The dowels came in .007,.014 and .021.If the indicator shows .012 runnout for example, then the crank is offset 1/2 that amount [.006] so you would use the .007 dowels which would get you withiin .001. It is easier to do than to explain.
If you have an MP catalog you can find the dowels in the tranny section .
I don't know if they are still available or not.
 
Well thanks for all the advice. I bought a new flex plate and installed it last week. Everything lined up just fine and no balance problems, seems to run just fine. I also used locktite on the torque converter bolts. I'll keep an eye on it and pop the inspection plate off from time to time.
 
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