G56 Transmission knocking noise

[DPratt]

I have been looking at a 2006 with G56 transmission - 149,000 miles. Nearly ready to make an offer, and on my second test drive discovered that with engine running in neutral and clutch out, the transmission was making a knocking noise. As soon as I pushed the clutch in, noise went away. This struck me as a deal breaker, but I am interested to know what this noise was. Can anyone advise? Thanks, Dave Pratt

 

[SierraRam]

Does it have an aftermarket clutch? Mine has knocked for 60K miles since I put the Southbend clutch in.

 

[seafish]

If the transmission and clutch are stock, it is very likely a failing dual mass flywheel, which is a fairly common and eventual failure on the G56 transmission.



If the truck is OTHERWISE in good condition, it does not have to be a deal breaker, though you will DEFINITELY want to replace the clutch and flywheel with a quality upgrade, maybe one from Southbend Clutch, that uses a speciaclly designed standard flywheel and ONLY quality clutch, bearing and hydraulic components. Even if the knocking that you are hearing is "only" something wrong with the throwout bearing, you will need to pull the transmission to fix it and it is a dam good time to upgarde the clutch ANYWAY. Either way, it ought to knock at least $1200 off the price of the truck, if you can do the work yourself, or $2000 if you will have someone else do it.



ON EDIT--



ACTUALLY, if the truck has had power upgrades added to it and been used for towing, you may well want to avoid it, becuase it IS possible that if the DMF has been failing for awhile and if the transmission has been unsed in highly load conditions, that the actual aluminum case of the G56 may be ruined, which is something you won't fiond out until you get into it and will cost MUCH more then the clutch repair. This is likely ONLY in over powered or highly loaded conditions for the g56, so if the truck is otherwise stock and NOT seen an extensive life as a tow vehicle, then the transmission case is likely OK. In general, anyways, it is MUCH better to buy a trcik that has been UNmodified, at least to the powertrain.

 

[CKelley1]

the above is correct. the dmf on most failed before warranty was out. most of us changed to a smf at our cost rather than put another dmf in under warranty only to have it fail in another 50,000. i have never heard of one lasting lasting 149,000 miles so i bet you must have a smf. the noise is natural and you just have to live with it.

 

[DPratt]

Here is some additional info. The clutch was recently replaced with a South Bend 'dual disc' (I hope I remember that correctly). I don't think the truck had power upgrades or worked hard, but no way to tell. There are no signs I could see of a tuner, gauges, or mechanical changes The current owner bought it out of state on speculation. Also, I noticed that when the clutch was down, there was a noise that sounded like a throwout bearing failing but he told me this is common with this clutch setup. It was the knocking in neutral that worried me most. Thanks for all you replies Dave

 

[CKelley1]

you got the best. it is a 3250 dual disc

 

[HBarlow]

Here is some additional info. The clutch was recently replaced with a South Bend 'dual disc' (I hope I remember that correctly). I don't think the truck had power upgrades or worked hard, but no way to tell. There are no signs I could see of a tuner, gauges, or mechanical changes The current owner bought it out of state on speculation. Also, I noticed that when the clutch was down, there was a noise that sounded like a throwout bearing failing but he told me this is common with this clutch setup. It was the knocking in neutral that worried me most. Thanks for all you replies Dave

A sharp Cummins tech in a Dodge dealership can tell by plugging the truck in their computer and reading out all the parameters. Among the data they can read is the hours and percentage of time the engine has been run in each ten percentile range of power output for example, 35% of hours run the engine was operating at 40% power. A sharp tech can also see evidence of magic black boxes being installed by looking at things like hours of run time vs. odometer miles driven. There is more that I don't remember or didn't understand when it was explained to me. Some Dodge dealer techs wouldn't recognize a Cummins engine next to a Packard convertible but a sharp one can tell a lot from computer data available on the dealer computer.

 

[SierraRam]

Here is some additional info. The clutch was recently replaced with a South Bend 'dual disc' (I hope I remember that correctly). I don't think the truck had power upgrades or worked hard, but no way to tell. There are no signs I could see of a tuner, gauges, or mechanical changes The current owner bought it out of state on speculation. Also, I noticed that when the clutch was down, there was a noise that sounded like a throwout bearing failing but he told me this is common with this clutch setup. It was the knocking in neutral that worried me most. Thanks for all you replies Dave

That is normal for that clutch, I have the same clutch and it has made those noises since it was installed 6 years ago. The dual disc clutches are very noisy but man the work well.

 

[RVTRKN]

Here is some additional info. The clutch was recently replaced with a South Bend 'dual disc' (I hope I remember that correctly). I don't think the truck had power upgrades or worked hard, but no way to tell. There are no signs I could see of a tuner, gauges, or mechanical changes The current owner bought it out of state on speculation. Also, I noticed that when the clutch was down, there was a noise that sounded like a throwout bearing failing but he told me this is common with this clutch setup. It was the knocking in neutral that worried me most. Thanks for all you replies Dave

That noise is common with the SBC DD 3250 and the solid flywheel does not have the dampening effect like the DMF. If it was changed recently then more than likely the pilot and throw out bearings were changed. It is true that the aluminum case can flex and cause damage, but that is under extreme usage, like running at 30K GCVW and or black boxes installed. Have your mechanic look at it for a better evaluation. If you negotiate the expense of a clutch in the purchase, when you pull the trany have it opened up and inspected by a qualified trany shop. If you plan on towing at Dodges GCVWR or more, have a girdle installed on it at the time it is reinstalled in the truck. That way you know the trany is sound and will be protected in the future.

 

[JHumphries]

Has anyone thought about what modifications have been done to this truck to NEED a dual disc clutch.
That would be my biggest concern. What mods and how was the truck used? Unfortunately, with a used truck at a dealership, that information will probably not be available.

 

[RVTRKN]

The DMF's are prone to failure and if you tow any kind of heavy weight that is a good replacement, and is more than likely what happened.

 

[HBarlow]

Has anyone thought about what modifications have been done to this truck to NEED a dual disc clutch.
That would be my biggest concern. What mods and how was the truck used? Unfortunately, with a used truck at a dealership, that information will probably not be available.

That is a good question that should probably be answered before purchase.