Please help with noise diagnosis....

[75Chevy90Kawi]

i asked this in the engine/drivetrain forum, but in 3-4 weeks i got zero replies. and you guys have helped me before

first off, it's got the original th350 in the truck, but it was rebuilt when the crate motor was dropped in by the previous owner, which was about 8k (i think...) miles ago.

in january i dropped the tranny and replaced the torque converter after the bolt holes stripped. before they stripped, when i shut it off, about 3/4 of the time it would make a sort of clanging noise a few times when i shut it off.

a few weeks ago my truck started making a bad rattling/buzzing noise at about 1300 and 2300 rpm, (and a little bit every once in a while at 700) and two or three times has made the clanging noise like it did before, although not as bad (dont think it's a high idle either, but i do need to adjust the timing a bit, i just dont have a timing light). as far as i can tell all 3 bolts are in the TC good and tight, and although i havnt looked very closely, i cant see any cracks in the flexplate.

i havnt really driven the truck in a few weeks because i want to find out what's wrong before i REALLY break something. i THINK it only does this in gear, but since i havnt driven it in so long it may be that it does it in neutral and park as well (but i'm pretty sure it doesnt, i'll check tomorrow).

i have yet to go through and check the drive train all the way from crank to rear end, (also something i need to do tomorrow) but was wondering if anyone can offer any insight into what this could be.

you guys have been big help before. one more time perhaps?

thanks
mitch

[79BIG10]

If you think that it's coming from that area I would check the starter for being on tight. Mine has come loose before and a little blu loc tite (not the red) and it was fine. Also check for your emergency brake cable(s) being loose. Mine were dragging on the exhaust pipe before and made a clanging.

[f.monroe]

Torq converter bolts are loose again, the flexplate is cracked around the crankshaft bolts ,the flexplate is in a bind , or the 6 bolts that hold the trans to the block are loose and backing out . It shouldnt take but about 1/2 hour to check what I have mentioned and you might find your problem . Frank

[Russell]

Originally Posted by f.monroe

Torq converter bolts are loose again, the flexplate is cracked around the crankshaft bolts ,the flexplate is in a bind , or the 6 bolts that hold the trans to the block are loose and backing out . It shouldnt take but about 1/2 hour to check what I have mentioned and you might find your problem . Frank

I'd agree, you'll find it in your flex plate etc

[75Chevy90Kawi]

Thanks! i'll check that tomorrow. hope it's not pouring rain outside... is it possible to change out the flexplate without dropping the tranny?

[Slonaker]

I had a noise kind of like what you describe. Mine was a slightly bent flexplate. It would occasionally hit the snout on the starter, making a horrible noise.

The transmission has to be removed to replace the flexplate. We did my friend's truck in just a few hours and we have never been mistaken for mechanics. It isn't so bad because you can just slide it back, replace the flexplate, and slide it back together.

Slonaker

[75Chevy90Kawi]

well when i replaced my torque converter it took me and my friend nearly a month working on and off, because the only tools we had were a set of wrenches and 2 floor jacks, and really VERY little experience with it.

[75Chevy90Kawi]

well the bolts from the bell housing to the block were all in good and tight, and the starter seemed fine. I was able to tighten the TC bolts just a LITTLE bit (maybe 1/4 or 1/3 turn) by hand, but they were by no means "loose". due to the wet ground, cold, and lack of a flashlight i didnt chekc the flex plate yet. i'll do that in a little bit.

and excuse my ignorance, but if the flexplate is "in a bind" what does that mean?

thanks again everybody

[marvxyz1]

The clanging could be coming from your drive shaft. The front yoke could be hitting the catalitic converter heat shield. It happened to me and I thought my transmission was going bad, big time. Probable cause was deterioated transmission mount.

[piecesparts]

Check to see if the starter drive gear is too close to the flexplate. If your noise shows up when you accelerate it could be due to the flexplate moving forward as the torque converter balloons. Sounds funny, doesn't it? I had this problem on my 91 Chevy 5.7 and I had to change flexplates to a heavy duty SFI rated plate to stop it.

[75Chevy90Kawi]

it's not just when i accellerate, its any time i hit those certain RPM. so if i'm holding my speed, it will just vibrate until i either accelerate or decelerate. it got dark before i could go back out and check for cracks, so i'll look for cracks tomorrow and check the shaft at the same time

[79BIG10]

Originally Posted by 75Chevy90Kawi

is it possible to change out the flexplate without dropping the tranny?

Actually it is possible. You can take the tranny loose from the bell housing and the tranny crossmember. Then take some really long grade 8 bolts the same size as the bell housing bolts and replace them with the stock ones. Then slide the tranny back after unbolting the TC from the flex plate and then you can access the flexplate. Takes a bit of manuvering but much easier than taking the whole tranny out.