# 400 flywheel knock?



## scott9804 (Aug 19, 2013)

I have a 1972 Lemans Sport......and as much as I regret saying it, it's a GTO clone, just like all the others out there! Anyway, when it was cloned, the previous owner yanked the original 350 and put in a 400 with a TH400. After repairing a few leaks, clogged lines, and some brake work, I've got it running and driving again. It starts, runs, shifts, and drives smooth, but the only thing is a pretty noticeable "knock" in the engine/trans junction. I'm pretty sure it has something to do with the flywheel, because it does it ONLY in Park or Neutral, and ONLY on flat ground with no pressure against the transmission. In other words, if I am parking it on a hill, and I put it in Park with my foot on the brake, it immediately starts knocking, but when I let off the brake and it rolls forward (or backward, doesn't matter) to put pressure against the trans, it stops the noise just as quickly. Now, I've been reading where a cracked flywheel can cause similar symptoms, can this be my problem? Also, the previous owner had accumulated some spare parts that I was able to get my hands on with the car....he was intending on converting it to a 4 speed, so I have the 4 speed trans, bell housing, pedal assembly, and another flywheel. My question is this....If I can determine that I do indeed need a flywheel, would it be worth my trouble to try to use the one that came with the 4 speed? Are the flywheels/flexplates the same for 4 speeds and autos? I'm posting these questions here to try to find out as much as I can, because I can't ask the previous owner, he passed away about half way through the project. Any help will be appreciated.


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## ALKYGTO (Mar 29, 2010)

4 speed manual has a flywheel and an automatic has a flexplate. 

Your problem could be a cracked flexplate or merely loose flexplate bolts. Your trans should have an inspection cover and you can put the car on a lift or safely jack it up and put it on jackstands and see if all the flexplate bolts are tight. If they are loose, remove them one at a time and apply a little Loctite to keep them from backing out again. You will want to use a torque wrench also to make sure they are tight enough but not too tight to stretch the bolts or crack the flexplate.


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## Rukee (Feb 8, 2007)

I've seen many broken flexplates and loose toque converter bolts.


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## scott9804 (Aug 19, 2013)

Thanks guys, I'll check the bolts first, hopefully that's all it is.


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## scott9804 (Aug 19, 2013)

For anybody that might be interested.....it was a cracked flywheel. Apparently the transmission bolts weren't tight and it allowed the transmission to flex and cracked all the way around the bolt holes.:shutme


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## BearGFR (Aug 25, 2008)

Glad you got it taken care of

Now, how about some car photos?

Bear


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## scott9804 (Aug 19, 2013)

BearGFR said:


> Glad you got it taken care of
> 
> Now, how about some car photos?
> 
> Bear


I've tried twice to load some pics....not cooperating! I'll keep trying.........


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## ALKYGTO (Mar 29, 2010)

Upload your pics to a photobucket account and download from there.


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