Earlier this summer I had trouble with my dual mass fly wheel (story here). when the truck came out of the shop with the replacement, it also had acquired a very noticeable new noise. The transmission is a standard and the truck has about 230k miles.

The sound is what I would call a rumbling/growling sort of sound. It is only detectable when the truck is in neutral with the clutch NOT engaged or when towing under a load and the engine starts to dog down a bit, say below 1500 rpm or so. Engage the clutch the sound goes away, increase RPM, the sound goes away.

The transmission has been taken out and partially disassembled by a different local mechanic. He couldn't identify any bad bearings in it. I saw the tranny while it was apart, it looked pristine- nothing beat up that I could see at all. What should my next step be? The consensus is that this is a transmission issue, should I be 100% convinced of that or is it possible that the new flywheel is contributing? Another argument is that the sound was there all along and I just hadn't noticed it. If it was present before the flywheel episode I am certain that it was of a much lower intensity. So what do you think?

I depend on this truck and really dont want to replace the entire transmission if I can avoid it.

 

It's the gear rollover from the SMF.

Basically, the DMF took all the vibrations from the motor. With the SMF, they resonate into the trans and make a racket.

Its a normal thing. Nothing wrong. You can always dump in an extra qt of atf to help quiet it down.
mines went almost completely away.

So, nothing is wrong. =)
Just add some more fluid though the shifter hole and it will quiet it down a bit.

 

So I am to gather this is a common outcome seen when switching out the flywheels? I swear I should start a book listing all the things that everyone else seems to know that I don't. Still, would have been nice if the diesel mechanic had given me some warning about it....

 

your tranny will get used to the sound give it a couple thousand miles, the gear roll over will be almost or completely gone in neutral, but slowing down that growl wont go away. after a while you wont really notice it. it will quiet down a little bit.

 

Are there any potential issues from adding extra fluid? After Googleing the term gear roll over, I came across references to adding Lucas Transmission Fix; is that a good idea?

 

Stay away from lucas products, they just foam up your oil.

What about Additives?

I have 2 more than the book recomends in mine, a few others hear have more as well.

Just as long as you dont' fill it to the top, your good. But you have to do it though the shifter, not the side of course.