G56: Dual Mass v solid flywheel - which is better?

Hello all,

According to Phoenix Friction, switching to a solid poses no additional wear. This info is at:
http://www.phoenixfriction.com/t-do...esel-g56-transmission-clutch-kit-options.aspx

it goes into a bit nmore detail at:
http://www.phoenixfriction.com/t-in...ar-rattle-from-solid-flywheel-conversion.aspx

Do you all concur?

 

And I I’ll sell you the London Bridge? The gear rattle is mostly @ 1500 rpm for mine, if the gears are rattling enough to emit the noise I hear, then it will wear. I cushion mine with Mobil Delvac 50wt transmission fluid and try never to make that rattle. Standard Transmission rebuilt mine before my SMF, and I was warned not keep pressure on the trans during the rattle. Sometimes it can’t be helped, when it ralttles keep a soft throttle until your passed 1500 rpms. Would I go with SMF again? Yes! Do I like the DMF? No

Just know the ATF in your trans is too thin and lite if you go to a SMF, and the transmission will be a lot noisier.

 

Having owned both in my 05 with the G56 I can tell you The factory unit is smooth and quiet until it fails and they do fail. I went with a solid flywheel unit from SouthBend. My only complaint was it was very very grabby it was hard to slip it for smooth engagement it was release and go. Some times it was fun backing up hills pushing the trailer. I couldn't tell if there was any more noise from the gear. I had expected the worst an was pleasantly surprised.

 

Would that clutch be the SB OFE? Sounds like it.
The OKHD they offer is pretty smooth.
When my truck was new I talked to LUK about offering a 60+ hp dmf.
The trans was nearly silent with the stocker but it didn't have that additional clamping power I wanted.

 

It's been a few years since I had it installed but I think it was the SB OFE kit.

 

okay I admit that this is perhaps a dumb question but I truly would like to know... if the factory unit is smooth and quiet until it fails then why not replace it with another factory replacement unit?

At what mileage did the flywheel fail?

I have the g56 in my truck but I couldn't tell you what a dual mass flywheel is - or why we have one in the first place. Educate me please.

Thanks in advance.

 

I have not had a problem with my DMF. And I don't plan on towing heavy enough to destroy it.

So I don't have info on when they fail.

But the dmf is prone to fail because it is a 2 piece flywheel. And anytime you have 2 pieces instead of 1, and you put a large load on a 2 piece mechanism where the pieces rotate independently, there is a higher likelihood of failure.

But more specifically for the Ram/Mercedes G56, many who tow heavy find the stock clutch springs just don't force the pressure plate against the flywheel hard enough to keep it from slipping. And the DMF can not handle the stronger springs that people like to upgrade to.

The DMF is advantageous because our diesels run at lower RPM than most gasoline engines and as they run, they speed up and slow down. The DMF absorbs the vibrations caused by the irregular rotational motion at virtually all rpms.

Above, you will see that RVTruckn likes to avoid rattling his teeth at 1500 Rpms and chooses to run his single disk at faster speeds under load because of the vibration.
Actually, the transmissions receives much of the vibrations. And It's debatable how well the aluminum cases G56 handles those vibrations. It seems to be doing well, but I imagine the NV 5600 was better.

 

It's not a matter of if but when a DMF will fail. They are a wear item much more so than a standard flywheel. The DMF on the wife's TDI failed at 200k miles. Initially I thought it was the clutch disc given that everything was still original. Upon disassembly all clutch components were still in great condition and could have easily gone another 30k given the remaining lining on the disc. The cause of the chatter was a twisted DMF. Makes it interesting getting to the flywheel bolts when that happens!

 

i just "upgraded" to a SMF from SB, i got the hd ok, kit, every one says you get gear role over noise, well i only do down around 8-900 rpm. anything above that, and it's just as quiet as the stock one was.
my stock LUK clutch lasted 168K, and was still good aside from me slipping it from turning up the HP. when removed the DMF was still in great shape, as was the disk, I kept mine in case i ever decide to go back to stock.
my SB drags on the input shaft some making it hard to get into 1,2,R at idle. but other than that its a smooth shifter.

The DMF is designed to absorb the pulses from the engine firing. each cylinder fires and creates a pulse, the SMF will make these pulses show up in the gears of the trans.
I also switched fluid away from the ATF+4 to Swepco 711.
If at stock power levels, I see no reason the stock clutch wouldn't last a long time, 200K maybe.

 

Okay thanks for the info. No wonder the G56 trucks are derated compared to the others.

 

I will likely replace both my clutch and DMF at the same time. Probably around 150k. Just makes sense to do both while you've got it apart. It's a toss up on which will go first. Might depend on the driver. I did some uphill backing of a trailer at a few state parks. And had to make a few runs at it. I don't expect my clutch to outlast my dmf. I really don't like that first and reverse have the same gear ratio. I think reverse should be lower/slower.

 

Parts are really cheap on Summit Racing for the stock dmf.

 

the stock unit on the 05 I use to own had lasted 138,000 miles. It's failure was it started to slip on a hard take off. If I babyed it it would grab an get me moving. When we removed it everything was worn out. The vibtation springs the auto slack adjuster, everything. I never had to replace the south bend unit so I couldn't tell how long it would last I just know that aside from the grabby ness after a spell of high humid days itr was a great unit. I never really noticed any extra noise.

 

Changed mine at 12k miles due to the fact that I tow very heavy with a Southbend DD3250. Dump trailers are often in the 25k range, race car trailer is almost exactly 32k, and occasionally I do something stupid like moving a 26k# man lift from one job site to another (grossing about 40k). I knew my DMF was GOING to fail. I obviously baby it when I'm loaded heavy. The stock clutch did hold up fine for 12k miles (meaning it didn't break) but I did see signs of slipping when we took it apart. I'm pretty easy on parts as a driver and for example, I got 200k out of my CON O on my old 12valve NV4500 (Trans wears out faster than the clutch!) and we only changed it for reliability reasons. It wasn't worn out. Southbend makes a nice product. The Dual Disk is a little noisy (even the quiet one) but it is extremely good driving. Never bucks at all. If you have a 4wd, and tow heavy, the BD 2-low kit (13+) is almost a must either way. I CAN back up a trailer slipping the clutch but that isn't good for anything. The 2-low allows you to get you foot off the clutch pedal. The more you drive thinking the clutch is a toggle switch (and can still drive smooth) the longer it will last. Get your foot on and off it quick (while being smooth and rev matching) and it will last. I'm not sure you can get that kind of reliability with a DMF.
On anther note completely, you would be amazed how hot a G56 will run at any weight, especially in 6th gear. Mine would run 240+ on level ground even at low weight (under 20k). You have to figure the engine runs 200* and the transmission will eventually equalize with it since they are bolted together. I added a recirculating cooler to at least keep the fluid in the 190-205 range to match the engine. Truck only has 28k on it now but we'll see long term how everything works out.

 

I found mine to get that hot at 10K GVW. Very good advise, and I recommend all G56 owners to install a cooling system. Aluminum will soften when it gets hot, and the torque applied to a G56 can cause the gears to misalign when hot. This is a major flaw in its design.

Brian, have you considered a girdle, because of such a heavy GCW? My 23K GCW doesn’t warrant a girdle, but at 40K, I would install one as well as a cooler.

 

My original DMF lasted about 198,000 miles. It's replacement failed at 4,000. Only one of its springs was still where it's supposed to be. I had SMF conversion installed, and with some adjusting to the way I shift the gears (never lugging), there isn't as much vibrating as I expected. According to the mechanic, DMF cannot be resurfaced.

 

I honestly am not considering the girdle. The only reason being is that steel and aluminum expand and contract at different rates, in my humble opinion, they are probably good to help prevent breakage for sled pullers and what not, but I believe that the loading it could provide in some area and not in others could cause long term wear by pushing or pulling where it shouldn't or unevenly. You aren't going to stop the aluminum from expanding completely so in my opinion, you are squeezing it in some areas, not in others, and probably pushing on some areas that probably shouldn't be under "normal" circumstance. I believe the wear this could potentially cause is probably only going to if anything be offset by the load wear it might benefit. I really don't lean on it too hard when that heavy and I've only got an extremely mild single injector event tune in it so I'm going to take my chances. I'm anxious to see long term how our loop coolers (with real filtration) help the G56s out. I think the localized overheating is what causes most of the failures. Hopefully in another 200k I'll have the same opinion!