Allison 5sp: Cracked flexplate?

standy

New member
Jun 22, 2009
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Royal Oak, Mi.
I have been chasing a noise for a couple weeks now, and from what I have read so far, the noise might be a cracked flexplate. It is intermittent-meaning some days it is very audible, and other days, I can't hear it at all. The best way I can describe it is to say that it sounds like a rythmic tapping of a broomstick on a piece of aluminum. It is loudest in gear at idle, still audible in neutral and park, and will go completely away just above idle...under load, there is no noise. I made sure that all the converter bolts were tight (oddly enough, the noise seemed to go away for about two weeks after I did this), and also did the best visual inspection that I could with the transmission still in the truck. One thing I noticed today while looking to see if my Suncoast converter had a drain plug, is that I have some forward and backward movement of the converter and flexplate. I would say that i can move the converter between the bellhousing and the back of the engine a little under 1/16th of an inch or so. I should also note that the flexplate moves with the converter. My question is: is this movement normal, or is it a sign that i have a damaged flexplate?
 

Mike L.

Got Sheep?
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Aug 12, 2006
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Some converters rattle and some don't. If that's what it is. it won't hurt anything.
 

Lb7KID

ZoomZoom
Jan 24, 2010
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parker,colo
i had that noise to once i thought it was the t.c so went out bought a new one from ats:eek: got home pulled the trans put the new t.c on hoped back under the truck to check see if rear main was leaking an what not look at the flex plate and it was crack haha right on the dumb little sheet metel part that the t.c bolts to. needles to say i got a built one an a new t.c no more ting. almost pos that the noise i heard was from my flex plate
 

standy

New member
Jun 22, 2009
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Royal Oak, Mi.
Thanks for the replies, guys! Hey Mike, I should've mentioned that it is really loud when it happens....I can hear a pronounced knock from about 50 feet away. I have about 45k on this converter (1057), and it just started making the noise in the last 7k miles or so. Do the converter clutches make noise from the start, or can it get louder over time?

At any rate, I hope its the converter, because I really don't want to pull the trans out anytime soon if I can help it. For the guys who have broken flexplates, where do they crack.

Oh, I almost forgot- Would I be correct in assuming that the recessed allen head plug in the converter is the drain plug?

Thanks again for the help guys!


Andy