I've had my hot rod at the dealer twice in the past week due to a failing DMF. Of course everything is peachy while in their hands and then magically shakes after I get it back. Is there is a factory procedure for diagnosing a bad DMF I can point these guys to? For whatever reason they just don't want to believe the flywheel can cause the vibration issues I have. At least the tech was honest enough to admit they don't see manual Duramaxes come in for service.

The only sure-fired way to tell in my experience was the rattling sound it made when you barely push the pedal. I never had any vibration due to the DMF.

Watch your gear stick and see how it moves.

If if is jumping all around rather than sitting still, your DMF is toast.

GM have or at least had a Technical Service Bulletin on the symptons of a faulty DMF back in '04 and fortunately for me the contents of that SB were either published on this Forum or directions given as to where to find it because I familiarized myself thoroughly with the symptons before I took my 2004 Duramax equipped Chevy to the Dealer in Oct 04 with just under 8,000 Miles on it. Armed with that knowledge, I had no difficulty whatsoever in convincing them that I needed a replacement DMF and I'm happy to say that I haven't had any problems with the replacement unit which was supposedly a better engineered DMF than the OEM that came in my truck. The replacement DMF was GM Part #24232434 Unfortunaley at this late date, I don't remember the symptons other than clunking and grinding bearing sounds coming from the flywhell area of the vehicle particularly when decelerating down thru 1200 RPM. Hopefully you can find that TSB

Is this it???


Excessive Shifter and/or Engine Vibration, Bearing Growl and/or Rattle Type
Noise While Depressing or Releasing Clutch Pedal (Replace Flywheel and
Flywheel Mounting Bolts) #04-07-31-006A - (Dec 9, 2004)
Excessive Shifter and/or Engine Vibration, Bearing Growl and/or Rattle Type
Noise While Depressing or Releasing Clutch Pedal (Replace Flywheel and
Flywheel Mounting Bolts)
2001-2005 Chevrolet Silverado

2001-2005 GMC Sierra

with 6.6L DuramaxT Diesel (RPOs LB7, LLY) and Manual Transmission (RPO ML6)

This bulletin is being revised to add the 2005 model year, VIN breakpoints
and include the replacement of the eight flywheel mounting bolts. Please
discard Corporate Bulletin Number 04-07-31-006 (Section 07 --
Transmission/Transaxle).

Built Prior to the following VIN Breakpoints:

Plant
VIN Breakpoint

Flint, MI
5F836256

Pontiac, MI
5E148789


Condition
Some customers may comment on a bearing growl or rattle-type noise while
depressing or releasing the clutch pedal. Some customers may comment on
excessive shifter or engine vibration. In some cases, the excessive
vibration may result in an injector balance rate fluctuation condition.

Cause
The steel clutch thrust washer may wear down the flywheel bushing
prematurely, causing an excessive vibration condition.

Diagnostic Tips
The bearing growl/rattle-type noise and or vibration is eliminated with the
clutch fully engaged or disengaged.

Correction
Replace the flywheel assembly with a Dual-Mass Flywheel, P/N 24232434. Refer
to the applicable SI procedure below.

Important: The eight flywheel mounting bolts, P/N 97226124, must be replaced
when service requires removal or replacement of the flywheel.

Heymccall's post although published after my DMF was replaced describes the contents of the previous TSB pretty well to the letter as near as I can remember which resulted in my DMF being replaced by the dealer with no difficulty whatsoever.

2004.5 LLY E/C SB ZF6 Prodigy Brake Controller

Member #55 of the Brotherhood of Handshakers

I don't have it in front of me, but my dealer came back with a TSB that basically says the vibration I'm getting is caused by lash in the drivetrain and is a characteristic of manual transmission equipped vehicles. There is some plausibility to that explanation as I don't get the excessive shifter shake and the condition is still pretty intermittent.

Do I get a gold medal or anything cool for making it 100k miles on a stock DMF?:D

What is a DMF?

Dual Mass Flywheel

Utilized to quell resonant vibrations that are present in a diesel engine's cranksahft from being transferred to the transmission. This results in less noise and vibration through the shifter, and more importantly, results in less wear through the transmissions bearings. Without the DMF, the bearings can actually chatter their mounting bores out of the case assembly.

Once again thanks heymccall