I have the ZF-6 six speed in my 05 3500 Duramax Dually. Whenever I change gears, there is a "clankety-clank" for lack of a better term, when I clutch it and take the pressure off the drivetrain to change gear. I had the truck in for something else and told the service writer about it and he said it was normal. It also rattles when clutched and the truck goes over a bump in the road. Could something be loose in the tranny? The service writer said it had a "centrifugal clutch, kinda like in a go cart, so if the drivetrain gets in a bind, this lets it slip and keeps it from damaging the drivetrain" I don't know whether I buy this. Here at work, we have a duramax 6 spd, regular cab 2500HD, and i haven't noticed the noise with it. I do realize that mine has a longer 2 piece driveshaft, though, giving room for more driveline play. Any help would be appreciated as I tow a camper and if whatever it is lets go, I could be hundreds of miles from home. Thanks

I have the ZF-6 six speed in my 05 3500 Duramax Dually. Whenever I change gears, there is a "clankety-clank" for lack of a better term, when I clutch it and take the pressure off the drivetrain to change gear. I had the truck in for something else and told the service writer about it and he said it was normal. It also rattles when clutched and the truck goes over a bump in the road. Could something be loose in the tranny? The service writer said it had a "centrifugal clutch, kinda like in a go cart, so if the drivetrain gets in a bind, this lets it slip and keeps it from damaging the drivetrain" I don't know whether I buy this. Here at work, we have a duramax 6 spd, regular cab 2500HD, and i haven't noticed the noise with it. I do realize that mine has a longer 2 piece driveshaft, though, giving room for more driveline play. Any help would be appreciated as I tow a camper and if whatever it is lets go, I could be hundreds of miles from home. Thanks

No, that isn't normal...Centrifugal clutch? Funny, I havn't seen a pull rope hanging out my bellhousing to start the truck incase my starter dies ):h

How many miles are on this truck out of curiousity? My 01 came from the factory without having the transfer case bolted down :eek: That made the same type of noise you're describing..

There is a certain ammount of driveline "clatter" in these trucks, however, rattling when pushing in the clutch isn't normal. If you push the clutch peddle slightly,just put a bit of pressure on it, and it rattles, it may be a bad dual mass flywheel(do a search on this). Whatever the case, find a dealer with a service writer who knows and understands these trucks. This guy sounds like he couldn't pour water out of a boot if the instructions were written on the heel.

dont know how many miles you have on your truck, but check the vin break and see if your truck fits in.


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)

</TABLE>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 Duramax™ 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:

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Plant

</TH><TH vAlign=bottom align=middle>VIN Breakpoint

</TH></TR><TR><TD vAlign=center align=middle>Flint, MI

</TD><TD vAlign=center align=middle>5F836256

</TD></TR><TR><TD vAlign=center align=middle>Pontiac, MI

</TD><TD vAlign=center align=middle>5E148789

</TD></TR></TBODY></TABLE><A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss1-1576796">
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.

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss2-1576796">Cause

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

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss3-1576796">Diagnostic Tips

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

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss4-1576796">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.


<TABLE border=0><TBODY><TR><TD vAlign=top> • </TD><TD vAlign=top>Engine Mechanical - 6.6L (LB7) -- Engine Flywheel Replacement - Manual Transmission (SI Document ID #1217874) </TD></TR></TBODY></TABLE>
<TABLE border=0><TBODY><TR><TD vAlign=top> • </TD><TD vAlign=top>Engine Mechanical - 6.6L (LLY) -- Engine Flywheel Replacement - Manual Transmission (SI Document ID #1364525) </TD></TR></TBODY></TABLE>
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss5-1576796">Parts Information

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Part Number

</TH><TH vAlign=bottom align=middle>Description

</TH><TH vAlign=bottom align=middle>Qty

</TH></TR><TR><TD vAlign=center align=middle>24232434

</TD><TD vAlign=center align=middle>Flywheel, Manual Trans., Dual-Mass

</TD><TD vAlign=center align=middle>1

</TD></TR><TR><TD vAlign=center align=middle>97226124

</TD><TD vAlign=center align=middle>Bolts, Flywheel Mounting

</TD><TD vAlign=center align=middle>8

</TD></TR></TBODY></TABLE>
Parts are currently available from GMSPO.

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1576796&pubid=1058&evc=sm#ss6-1576796">Warranty Information

For vehicles repaired under warranty, use:

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Labor Operation

</TH><TH vAlign=bottom align=middle>Description

</TH><TH vAlign=bottom align=middle>Labor Time

</TH></TR><TR><TD vAlign=center align=middle>J1420

</TD><TD vAlign=center align=middle>Flywheel (Manual Transmission/Transaxle) - Replace

</TD><TD vAlign=center align=middle>Use published labor operation times

</TD></TR></TBODY></TABLE>


<TABLE width="100%"><TBODY><TR><TD align=left width=778>GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
</TD><TD align=middle width=42>http://service.gm.com/engif/000/999/999/999999994.gif </TD><TD align=middle width=167>WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION
</TD></TR></TBODY></TABLE>
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Well, I just checked the vin, and it is 5F840, so it is after the one posted. It doesn't do it with the clutch exactly, it is when the tension comes off the drivetrain when you depress the clutch pedal. It doesn't do it every time, it sounds like play in the drivetrain. I looked under the truck and everything seems tight. My transfer case doesn't look like it is bolted to any crossmember, only bolted to the tranny. There is a crossmember under the transfer case, but no kind of mount to bolt the case to the crossmember. I wondered about that. Any suggestions??? Thanks to all (very Much).

Sorry, I forgot, the truck has around 1500 miles, and was doing this when I test drove it back in December. I just figured it was me as I hadn't driven a stick in a long time. This is the ONLY problem I have with the truck. It pulls my camper like a hausss. I can even run the A/C and still speed up on grades if I need to. This is my first diesel.

Well, I just checked the vin, and it is 5F840, so it is after the one posted. It doesn't do it with the clutch exactly, it is when the tension comes off the drivetrain when you depress the clutch pedal. It doesn't do it every time, it sounds like play in the drivetrain. I looked under the truck and everything seems tight. My transfer case doesn't look like it is bolted to any crossmember, only bolted to the tranny. There is a crossmember under the transfer case, but no kind of mount to bolt the case to the crossmember. I wondered about that. Any suggestions??? Thanks to all (very Much).

Look up through the two holes in the crossmember that mount is on. Just make sure the mount is bolted to the crossmember.
Also, does the truck do this in 4wd as well as 2wd or no?

Well, I've only had it in 4WD once for about a quarter mile when I first got the truck, in some snow. Can't remember, but it is driven daily in 2WD and does. I am at work and can't look right now, but I remember when I looked, the transmission bolts seemed tight at the crossmember, but I didn't use a wrench, just fingered it. I put my hand around the crossmember under the transfer case and looked and felt, and there is nothing between it and the transfer case but air. I recall reading in a thread somewhere about breaking transmission cases and someone said they wondered if it was because of the weight of the transfer case hanging off the transmission.

Well, I've only had it in 4WD once for about a quarter mile when I first got the truck, in some snow. Can't remember, but it is driven daily in 2WD and does. I am at work and can't look right now, but I remember when I looked, the transmission bolts seemed tight at the crossmember, but I didn't use a wrench, just fingered it. I put my hand around the crossmember under the transfer case and looked and felt, and there is nothing between it and the transfer case but air. I recall reading in a thread somewhere about breaking transmission cases and someone said they wondered if it was because of the weight of the transfer case hanging off the transmission.
The crossmember under the rear of the transfer case doesn't have a mount on it...The front one does...I just slid under mine, but it appears things have changed just a bit from 01..Now, the mount has studs on it instead of having bolts going up to to the mount..just check that both of the nuts are tight. If it is loose, I would think you could see on the crossmember where the mount was sliding/shifting.
Just for grins, try putting it in 4wd on a straight stretch and see if the noise goes away or stays the same..

I'll try that. I will also look tonight when I get home and see, but I think mine only had 1 crossmember under the transmission and 1 under the transfer case, the one under the transfer case not having anything bolted to it. I'll double check tonight and let you know. Thanks so much for your time and assistance.

mine does the "exact" same thing, i couldnt have described it any better than you did, mine even makes that noise when you hit a bump real hard, if i had to described it i would probably say it sounds like a loose skid plate or somthing banging against metal, and i dont notice this all the time but i have been in the truck with it running and somthing would go thump,thump,thump.......and it wont stop until i push the clutch in. guess i should check it out before my warranty runs out

Okay, THAT sound is the result of slack in the driveline. You don't here it much in trucks with autos because the driveline is under force when the truck is in gear. With a manual trans it is only under force when under power. When you let off the throttle, the load comes off of the driveline and it's free to move a bit. Get under the truck and turn the driveshaft back and forth and you'll see how much play there is.
You can drive over some bumps and hear it, then go over the same bumps again, but take it out of gear first and you'll not hear it cause the trans is not "connected" to the driveshaft. Each of the last four pickup trucks that I've had has done this(3 Fords and this GMC)and it is a normal characteristic.

Ok, thanks a lot, im glad to hear that, maybe i dont have any flywheel problems then

try going over a bump at the same speeds but take the shifter to neutral and hold the clutch pedal down. If you don't hear the same noise/rattle then what you have noticed is slack/lash in the drivetrain. I used to notice a lot of this off-roading down-hill in the mountains with an old furd manny. I go over bumps on the way to work each day, I have learned to go do things differently. The lash no longer makes noise.

Sorry, but G.M. has a problem with the dual mass flywheel, and has had with the6.5's. they are working on a solid flywheel with a ceramettalic like what the medium dutys have.