Transmission/torque Converter Noise

jkotila · June 8, 2011

I have the following occur on a regular basis: After driving above 50 mph, I will let off the gas and begin to coast. At about 1500-2000 rpm, there is a horrid ratcheting/buzz sound from under the truck. At that point, the rpms will drop down to 1000 rpm right away. Sound goes away with a clunk if I punch the gas. Sound will not go away by applying brake, changing gears, or going into neutral. This will occur in either D or 3. This will also occur if tow mode on or off. My truck is a 2500 HD, 4wd, auto trans, 6.0 liter gas, about 120k miles. Trans fluid level is good and color is good. This has been happening for about 10 months. I was thinking it could be torque converter or soemthing in the TCC circuit. It seems to occur more often now, but still does not occur all the time. Please help before I really break something.

GMstrong · June 8, 2011

The clunk is the u joints on the driveshaft,as for the noise why do you think its the transmission or converter?does it shift fine?I think its the rear.

martinzel · June 9, 2011

could be a bad range fork in the transfer case.

jkotila · June 9, 2011

could be a bad range fork in the transfer case.

U joints are ok, I suspect torque converter because the rpms drop instantly from 1500 to 1000 when I hear the noise. The sound is not speed related, which I would think would take out most items past the output of transmision as @ 1500rpm in D I am at a different speed than I am at when I am in 3.

In regards to the range fork, what portion would maybe cause this noise? Because it is pushing the syncro over abit? I have had xfer case issues in the past, and had rebuilt.

Anyone have suggestions of what else to check. I appreciate all the suggestions so far.

jkotila · June 11, 2011

Any more ideas?

jkotila · June 19, 2011

Any more ideas?

anyone?

GMstrong · June 19, 2011

i know ujoints will make noise when your coasting and will go away under thorttle

jkotila · July 3, 2011

i know ujoints will make noise when your coasting and will go away under thorttle

U joints are all good, no slop anywhere in driveshaft or rear end. I have noticed that at low speeds, around town, trans goes click, clunk on and off when I am off the gas, usually starts around 1200 rpm. Sound is not consistent, it will clunk, then another clunk 5 seconds or so later. Clunks when in d, 3, 2. If I am in 2, the clunk gets louder/harder.

Torque converter? Trans?