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Discussion Starter #1
Hi all, some of you will know me from my C4 buildup info that I have posted here before, now I have a questions for you all.
What does it take to break the input shaft as I just had a guy that I built a C4 for break one and I am very surprised as I have never personally experienced this failure before. Is it really possible to break one with just a stock 5.0 HO EFI or could there be something else going on here that I have not seen yet? The trans is fresh has 5 clutches in each pack and has a forward pattern full manual valve body in it he chose to use a stock converter so it shifted very hard, but otherwise worked great, any thoughts on how to get the broken off piece out of the converter as it snapped off right there in the splines that go into the converter? I will be doing a thorough take down of the trans to check for any other damage and will let you know if I find anything unusual. Thanks All
Tim R
 

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Must have been something odd. I never broke one with a good 460 & I know of several with stock shafts faster. If all else fails PA sells a VERY hard one.
 

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With a full manual VB and a stock converter, I would think it would be a VERY harsh shift. I don't know it that is the reason it broke, but It could happen.
 

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I have twisted the splines on a stock input shaft when I had the C4 behind my 557 TBird. Fortunately I caught it before it twisted them off, they were twisted almost 1/4 of a turn.
 

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I ran 2 years with a stock C4 input shaft. First year was probably ONLY 500 hp, but second year was an honest 577 hp. Last year, (to cover my ass, just in case), I opted for PA's hardened input shaft.
Better safe than sorry. Hell, if you're worried in the least, just give PA a call. They're not that expensive..........especially for peace of mind!
 

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Is his bell housing centered correctly to the block? "using dowl pins" Was the converter bolted correctly to the flexplate? From hear-say the splines rip from the drum before the shaft breaks........most switch to a hard shaft to keep the splines from twisting "not breaking". He could have just have had a bad shaft to start with???
 

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Discussion Starter #7
Thanks for the input guys, I tore it down and found no other broken parts so must have been weak shaft or something in the converter and since I can't get the piece out of it, it to is junk. The guy had me upgrade the trans to roller planataries while I had it apart and is going to pick it up tonight. Later
 

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Discussion Starter #10
well he broke another one last night so I am sure it is something going haywire in the valve body causing a shift timing issue that is causing a lockup, most likely in 3rd gear intermediate band not releasing fast enough and high clutch grabing so fast that input is locked and with tight stock converter it just has to give somewhere and the shaft is what gives. Damn I wish I knew what to try next. I am afraid that if it is in the valve body the only fix will be different valve body or try some shift timing mods, but without a trans dyno to test it he is getting tired of taking trans in and out over and over till I get it right good thing it is a friend or I am sure he would be pissed off. Any ideas welcome wish me luck I will need it to figure this one out.
 
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