Noise from bell housing, transmission related...

[SilverXJ]

I have a noise coming from my bell housing.. and only the bell housing, particularly where the flex plate meets the crank shaft. It sounds like rod knock, but not as deep, more metallic sounding. It does it in park, neutral, drive and reverse. The frequency picks up as engine RPM increases. When the engine is cold it can barely be heard, you need to listen for it. However, when the Jeep is driven a bit and it is fully up to temp it gets louder. I can let it sit and idle up to operating temp and it doesn't get much louder. I used a stethoscope on the engine block and transmission and the sound is barely audible on either. I then removed the pointer end and used the open hose and it is the loudest (as far as I can tell) where the flex plate meets the crank. I did notice a bit of run out in the flex plate. Oh yeah.. and I had this same sound on the previous engine, just forgot about it until I got my new engine in... and the people that installed the old engine weren't exactly professionals so they could have possibly bumped or bent something.

I currently have the transmission removed. I saw no real damage on the flex plate, but I did see a ring, like a scratch, on the outer circumference of where the crank meets the flex plate, but it doesn't go all the way through. No real obvious cracks and prior to removal all the bolts were tight. The transmission is currently at AAMCO, which I have heard is fairly decent here. They saw no problem with the transmission pump and the torque converter passed a pressure test(I think that was the test). They recommend replacing the flex plate (which I will any how) and they also recommend replacing the torque converter...

Whats your take? could a torque converter create this kind of noise? Should I replace it?

-Chris

[Muad'Dib]

Did you re-use your old flex plate?

If so that has to be the culprit.

It sounds like the flex plate was cracked... are you sure that "ring" that you saw wasnt a hairline crack?

[SilverXJ]

Yeah, I should have replaced the flexplate when I had it out. But I will replace it this time around. And I don't know if that is a hairline crack or not.. Can't tell. I just don't know how it would have happened otherwise... it looks like there was a bur on the cranks and the flexplate was just slid around that bur creating a scratch... but that isn't how I installed it.. It could very well be a crack as it gets more noticeable when it heads up from being driven.

Anyhow, the flex plate has been handled by Titan so who knows... I know they had problems lining the engine up with the transmission as I saw them with a pry bar on the disconnected cross member. I'm no expert at installing a 4.0L, but I have never had to drop the transmission cross member to do it.

[SilverXJ]

Replaced the flex plat and the sound is still there. Have a torque converter on order.

[Muad'Dib]

Damn thats very strange .. i would have bet on the flexplate.

[SilverXJ]

I thought it was too rhythmic to be a flex plate. I did find a post where someone with a Toyota and the AW4 had a knock and it was his torque converter.

[Busey]

sorry to bring up an old post. I have the same noise and think it is the flexpate but I dont want to drop the trans twice. Was it the torque converter?
Thanks

[SilverXJ]

No, it was the cam bouncing back and forth in the block, echoing in the transmission bell housing. At least that is the theory. Pull your inspection plate and look for cracks in the flex plate and tighten the bolts.

[Busey]

Thanks SilverXJ- I need to swap the flexplate, it looks like it has a couple hairline cracks. I just want to check any other possible causes while the trans is out.