Heres one that might stump you.

[hemitodd]

Okay, heres the deal, a few years ago with the blessing of my wife, alot of overtime, and my brother-in-law getting me a 472 crate Hemi from chrysler, my dream for my Cuda came true.        the motor runs great

Heres the problem, at higher rpm i get a pulsating vibration,  and ive broken my second flexplate in 3 years.

The back of the torque converter is rubbing against the pump housing of the tranny(i circled it in blue where it is rubbing against on a spare transmission i have) its rubbing enough the metals turning blue from heat.

with the transmission bolted up square and torqued(the dowel pins are there) i can slide the converter back and forth between the flexplate and the tranny pump and there is 1/8 - 3/16" play before i bolt it to the plate.

ive tried two different torque converters........ same problem. you can see in the flexplate pic that it seems to be flexing until it fails.

talked to tranny shops and a bunch of people in the know and everyone says they've never seen it before.

Please tell me someone out there that knows whats going on?
 

[71chally416]

I remember a B&M "Super holeshot" 10" convertor I bought in the 70's had specific instructions in the box to grind that area on the pump in the picture for extra clearance. Most of the modern convertors don't seem to have that issue, but it's possible you have one of those old cores that did. Maybe our resident tranny expert can help out? 

Just a thought, I would check the thrust main on your engine. See if it has any noticable movement when you pull and push on the dampner.
If it's bad the crank might be able to walk far enough forward to cause problems. Ya never know....

[Supercuda]

Sounds like the dreaded, "ballooning convertor" to me. Usually the result of an internal failure of the convertor, but also sometimes due to excessive pump pressure, the convertor body is forced to "swell", and causes problems like you are describing.

[Moparal]

I cant tell by the pictures, but are you sure your not installing the flex plate backwards? It should slide the converter up to it close to a 1/2 inch. Not 1/16 to 3/16ths. If its backwards, this will do just that.

[craigsmytcudas]

check the thickness of your crank bolts ,your converter might be unseated from the back of the crank hub.this will pull the plate ears over back wards like i see in the pics . as others have posted looking for crank walk that would make sence except the plate ears would bend back twards your crank or engine block . if the pump had problems or an alignment issue your pump seal would dump fluid instantly .  i use arp crank bolts on my hemis 12 point heads ,i have used thicker bolts but when you install the 4 converter bolts  you will pull a bind and bend the flex plate .i also have had customers try and install the plate backwards because the bolts were to thick . all that said i lean twards the crank bolts .craig

[cudadave72]

Sounds like the dreaded, "ballooning convertor" to me. Usually the result of an internal failure of the convertor, but also sometimes due to excessive pump pressure, the convertor body is forced to "swell", and causes problems like you are describing.

[craigsmytcudas]

  if the  simple things to check that i mentioned earlier prove out as ok , and the converter is ballooned then i would check for blockage in the trans lines or bends or do a line pressure check .thats if the car is still running .the only other thing left is reduce line pressure .c

[JS27N0B]

All good advice.

How about the hub of the converter fitting properly into the rear of the crank? If the hub is not centering in the back of the crank it could also cause similiar issues.

[hemitodd]

wow, Thanks alot for all the advice. cool to have you guys helping me out

 i've never heard of a converter "ballooning".  but wouldnt that cause the shell of the converter to be forced towards the motor not back against the tranny pump?

the second time i changed the flexplate i checked everything carefully

-crankbolts head thickness was fine

-flexplate orientation was right although i thought you coulnd install one backwards because the offset bolt pattern     meant the bolt holes only line up if the plate is facing the right way.

- flexplate is seated flat against the crank hub

I'll check crank endplay but wouldnt the crankshaft have to be walking pretty far to start forcing the converter up against the pump housing wouldnt? if i got 3/16" play between the flexplate and the convertor when its not bolted that would mean the crank was walking upto 0.187" and i read once that the thrust bearings need changing when you get 0.012" - 0.015" play.



any other thoughts would be greatly appreciated

todd

[Chryco Psycho]

Ok so assuming the converter is not centered in the hub it woudl constantly flex the flex plate & could cause the vibration & cracking , I check this all the time on 4 spds But I am not sure how to check an auto , you may need offset dowel pins to center the trans correctly on the rear of the engine

[71chally416]

I've never seen it misaligned in an automatic if both dowels pins are in the block. It'll be a big problem if they aren't. Checking how the convertor hub fits into the crank hole is good advice too. Ya never know, maybe it was machined too big and slipped through QC

[Chryco Psycho]

I have seen new hemi blocks with poor dowel pin positioning
 for example known good belhousings that are out of line on new blocks

[71chally416]

That would cause his problem.....

[tactransman]

You must have a stall converter in it. Yes,you have to grind the pump some to make clearance on certain style stall converter "bowls" The converter and the flex plate are "fighting" for space and the converter is winning. I will see if I can find the literature on the grinding process.

[hemitodd]

thanks again for the support everybody ,

tactransman

i do have a stall converter in it(2200-2500 if i remember right), if the bellhousing and block are properly aligned for arguments sake, do you guys believe the flexplate is failing because when it makes contact with the part of the pump housing that sticks out it putting  uneven pressure on the flexplate or  because the flexplate is "flexing" back and forth too much.

 How much does a converter travel back and forth normally?