3L80 Rattle

[donquijote]

Not sure if you can hear it, but I have a rattle in one of my 3l80 transmissions. Sounds like its something internal, but it drives fine. The rattle is only at certain speeds and throttles, and it gets annoying. This tranny had this rattle when I got it, so I rebuilt it and it still has the same rattle. I'll probably take it to a local shop if it's not easy to identify. I'll try and get a better recording of the audio as well. Thx.

TH400 Rattle Sound

 

[kc5mzd]

sounds like the flex-plate is rubbing or sometimes they can get cracks and make weird noises. Did you replace the flex plate or just get the trans rebuilt from the torque converter back? When you removed the trans did you just unbolt the torque converter or remove the flexplate also? also some times a bent shroud cover will touch the flexplate. Sometimes if the shroud is installed with a bolt that is to long the bolt will rub...

 

[donquijote]

I put a new flex plate and torque converter on, and the sound is further back in the tranny past the TC it sounds like. The bolts matched the TM sizes. I'll pull the shroud off tomorrow and do a recording.

 

[Milcommoguy]

Shut it off and see if you can swab up a sample (rag, Q-tip on a stick) on the inside of the cover or look on the inside of the cover you removed for fresh fine metal filings. Might be a clue if you fine some. Exhaust heat shield is close by. Might be that? Does sound like something spinning thought. Once had a balancing weight sticking out (bad spot weld placement) that was hitting transmission casting. Would only do it at slow idle. When in gear or up to speed couldn't hear it. Guess there was a little end play. Good luck in the hunt.

CAM

 

[Milcommoguy]

Just went back to look at the video in slow motion. I believe there is a shinny spot showing up on the fly wheel. Might try rotating the engine with the bad boy breaker bar on the front damper bolt. Turning a quarter turn and lOOking very close at the motion rotation parts for HumV gremlins. CAM out.

 

[Dock Rocker]

Make sure it’s not one of the heat shields on the exhaust manifold rattling. I fell victim to that racket. I thought the transmission was toast. After accidentally making it stop it ended up being a 1 zip tie fix.


Sent from my iPhone using Tapatalk

 

[donquijote]

Ok, I checked all cables and items for the rattle and all good there. Removed the TC cover and noise is still there, so must be something inside rattling.

This is an audio clip holding my phone with the door open pointed at the th400. I minimized the lower frequencies of the engine rumble and you can hear it more like I can.
Th400 rattle audio

Startup without cover

 

[RetiredMarine]

I had the same noise and it turns out it was the Transmission Dipstick rattling inside the tube. I pulled the dipstick out and started it up, noise was gone. While it was still running I inserted the Dipstick and when I removed my hand, it started again. I hope it is just as simple for you.