what would crack a flexplate ?

[Guest]

What would keep cracking my flexplate? this is the second one in two years. The first time I accepted the problem as it being a original piece that finally broke due to 32 years of wear, but it broke again! I have a mildly built 402 w/350hp,the trans is a rebuilt 400at with a shift kit and a 2500 stall converter. Any input would be appreciated, thanks!

[alex's72fgmc]

cracking of the flexplate if fairly uncommon. flexplate have 6 bolts in the crank flange and 3 on the torque convertor. how is it cracking? straight in or at an angle? i would check the crank flange bolts and see if they worked loose or see if the flexplate is on backwards raise bolt area should face the torque convertor also take a look at the bolt areas and have someone turn the engine over and see if the flexplate and torque convertor wobble or if it is just the flexplate. if it is the flexplate only the mounting area on the torque convertor is out of spec/expensive paperweight.

 

alex

[Guest]

thanks for your advice

[Todd's 1972]

I had a friend with a 77 Chev pick up that had the same troubles. He finally found out what caused the flex plates to crack 150 miles in the middle of no where. It left him standed on the highway with a broken crankshaft it broke just before the rear main bearing. It ended up being a bent crank that was the cause of all his troubles. Mind you this may be worse case senario for your troubles. One thing to be aware of is if your motor has a vibration that you can't seem to pinpoint or get rid of a bent crank could be the cause.

[wallaby]

I agree. About the only thig that will crack a flexplate is bending motion. The name "flexplate" would indicate that the unit is designed to accept some bending, but if things are too misaligned it will break. The engineers have a neat name for this: Psycho-Fatigue. It means that every time a piece of material is bent, it "remembers", and is forever weakened that little bit. Continue bending back & forth and the piece eventually breaks. (I have used this method to break bailing-wire with my bare hands!)

The clue is in the direction of the crack. I know I have an alignment problem in an old 4x4 of mine. The bellhousing is at fault. The crankshaft and the trans input shaft don't meet up straight, they are just a little bit off, but it eventually will break the center out of my clutch. In my case, the result is a clean circular crack around the middle.

Take a look at the rag joint in your steering shaft and you can see the motion that happens when the shaft rotates out of line. Imagine that on the back of your engine spinning at 3000+ rpm!

First step is to be sure the engine and trans mating surfaces are clean, and there are no wires or debris clamped between the two pieces. Make sure that both of the big guide dowels are still there. These are important to align the trans to the engine; the bolts can't do it by themselves. Your problem could be as simple as a couple of loose bellhousing bolts.

[kmelton]

anyone who has not checked out todd's photos of his burple car is really missing a treat. georgeous car. what are your plans for lower trim?

 

(see his website in his profile)

[Guest]

Thanks alot guys !!! It means alot to me that you guys are willing to take the time to reply and help someone out, Thanks again for all of your input. Boy, I hope my crank isnt bent... Take care , Rod

[Todd's 1972]

Rocker, it may be a good idea to check with your local machine or tranny shop. They may know of other reason for your cracking flexplates. As wallaby stated it could be something simple that is the cause of all your troubles. I hope I didn't get you too worried but it could be something to be aware of. Good luck.

 

Kmelton I am slowly putting the bottom rocker trim back on but I am lacking in the free time lately. Hopefully over the winter.

[Guest]

thanks again !