Hard shift G56, Southbend Dual Disk.
 

Hey guys,
Been searching a lot for answers to my problems here.

Hoping you can help narrow it down and provide advice.

Got a 2007 5.9L with G56, and 124k miles.

My stock clutch started slipping so I put a south bend double disk in about a year ago.

Now the thing is getting really hard to get into gear, any gear. Easier when engine speed matches wheel/gear speed, but still tough.

I think it was significantly more difficult to get into gear right after the conversion, but now its getting worse.

( I believe that I did all the conversion steps correctly, not my first rodeo)

When I did the swap, i moved from ATF+4 to amsoil 75wt synthetic. Just swapped it back to ATF +4, but it didnt help much. Always over filled a bit.

Can only be a few things:
1. Synchros are shot.
2. Mass of the double disks.
3. Continuous dragging of the disks on the pressure plate or flywheel parts.

A few theories:

My clutch engagement point is pretty far from the floor, so I doubt its an issue with enough throw. Im gonna double check that though, and see if I can mess with it.

Synchros could be getting bad, BUT, why would all of them fail at the exact same rate???? AND why would they start failing so fast right after a clutch swap. (3rd can clunk if you go too fast, but the rest are fine). I have only driven about 8kmi since the clutch swap. Seem unlikely they would all fail together suddenly.

The added mass of the double disk clutch prevents it from spinning down very fast... that would make sense, but it doesnt seem to matter how long I wait, or if i drag lightly on the synchro for a while, its still hard to make the final pull in.....

Makes me think i must have a dragging problem. On a normal single disk clutch, if the pressure plate pulls plenty far away from the disk, it will stop dragging, no problem, ever. BUT with this double disk setup, you need the intermediate plate to back off and provide a gap for the disk closer to the engine. If I remember correctly, the intermediate plate is on pins.... what if the pins have rusted a bit, and the intermediate plate does not really want to move any more???.... that would make perfect sense for the symptoms described above.

The bigger question i have is, regardless of the actual failure mode above, it seems my problems are either due to, or greatly accelerated by the south bend double disk clutch setup. AND, south bend has a FAQ section a mile long published specifically to problems people are having with the G56.
Clutch Troubleshooting
I also have some absolutely absurd noise coming from the tranny with this new clutch setup under good load and under 1500 rpm... Adding a "song" never really bothers me, but that kind of resonance does not sound healthy at all.
So,
It seems like LOTS of people are having problems with the south bend double disk on the G56.... I REALLY do not want to pull the tranny again, fix something, and then have another major problem in another 10k miles..... I bought the South Bend so that it would last LONGER than stock.
My 92 dodge cummins has 300-400k miles on it with WAY fewer issues than the 07.

Any thoughts are much appriciated.
THANKS!

Did you also upgrade the hydraulics? If not then that is your problem. If so then they "may" be failing and causing your problem.

Is the sound you hear the gear rollover that they talk about in their FAQ

The "song" isn't healthy at all. Mercedes designed that transmission to have the torsional spikes absorbed by a Dual Mass Flywheel.

After 1 year and 15k miles on a SouthBend single disk kit (that failed just outside of warranty), I had to pay to have my G56 rebuilt. I'm back to an OE clutch setup and couldn't be happier. Wish I hadn't wasted thousands on the after market and the damage that ensued when I could have just replaced my clutch and DMF with OE style LuK setup for $500 and been done.

Here's my saga from last summer:
https://www.dieseltruckresource.com/...ite-up-318715/

rockcrawler304
Yes,
The hydraulics were upgraded at the time of the clutch conversion. Full kit from SBC.
I am certain the sound I am hearing is the same described in the FAQ section published by SBC.

Jona Gold,
Your experience is really scaring me. That is the worst case scenario that I absolutely do not want to deal with. Besides the hassle, It implies that upgrade is simply does not work, and is fundamentally flawed.
I have a call in to SBC, hopefully they can help, but they have not called me back yet.

I don't surf these boards too often, Do the majority of SBC dual disk conversions with a G56 have problems??? or are we an unlucky minority?

I don't see any power adders in your signature, so I'm curious why you jumped to a double disk clutch? Just for longevity and reliability?

I've read several posts on this and other forums in the last couple years about South Bend clutches failing sooner than the owner thought they should. Most of them call Peter, and he "hooks them up" with deals on upgraded replacement parts, etc. Customer is happy and raves about their great service. The customer still ends up spending a good chunk of money/time on parts and labor to fix the problem. In some cases like mine- thousands more, thanks to a transmission rebuild.

From what I've seen reading these posts over the last 18 months, 80k miles is about how long the after market clutch kits last on average. Most guys are pushing more power, so its hard to guess how long the stock would last in the same truck- maybe half that? Maybe it doesn't really matter since they are pushing more power than the stock setup can even hold. So I get why they think the SB or similar single mass flywheel kits are so good, and that's why I backed off adding any further power to my truck. It already had plenty for my needs, and I value the longevity, reliability, and fuel economy over being faster or able to tow more.

For me, running only slightly more power, 100k+ miles on the OE style kit with a DMF that costs half as much and makes the truck more enjoyable and economical to drive is the better investment.

Just updated my signature.... should explain things better.

My goal is not big power, but i did finally get an edge tuner.
That was a likely contributor to the failed stock clutch.

I actually always hated the dual mass, you can feel it spring around when you are sliding the clutch. You end up loosing some control and fidelity, especially if you like to minimize slippage and get the clutch all the way out at lower RPM. I totally prefer the feel of a single mass. So that was one of the reasons i upgraded.

Based on all the chitter chatter on here, I assumed the SBC double disk was legit, and expected it to last longer than the stock DMF. I usually subscribe to the idea that the popular aftermarket upgrades solve problems, and not cause them. (with the exception of big power bumps).

I also had a neighbor that went through 3+ stock DMF setups before he did an aftermarket upgrade((Cant remember which) and now he is not having clutch issues anymore.

I've got 35K on my SBC OKHD. Silent operation. Aside from gear rollover noise putting though the neighborhood or a parking lot I can't complain. I carry 2K# on my back constantly,34" tires and have Smarty cranked up to sw#7 default. 5th floored will not slip. I agree with Jona Gold though on the vibe absorbing advantage of a dmf.
I feel there's a market for a 65hp+ dmf for these trucks that would go 100K. I asked LUK for one eight yrs ago and NOTHING. Come on SBC or Valair.[laugh]

I was waiting for a full year and 15k miles to update my original thread (I'm at 14k), but I will post a quick update here.

I'm still running my Edge Juice w/Attitude- still use #3 setting fairly frequently. Bought a camper last spring, and two new trailers for working on my land, so I'm towing much more frequently. Not a slip, noise or vibration from the LuK kit I bought- but it should be noted, the LuK kit is rated for 850 ft/lbs of torque, not the stock 610 my 06 puts out without the Edge Tuner turned up.

Danderson- maybe this new LuK kit is what you asked for- with really crappy marketing. Horsepower is just torque over time after all- and the LuK kit has no official "horsepower" rating.

Diesel Junkie- I've never had any of the feelings you had with your factory DMF, but I understand your concern better now. As for your neighbor- I don't think all trucks or parts are built equally (as was evidenced by a relative with almost the exact same truck as mine but his was always breaking), and certainly the parts installer, and the driver can make a big difference too. There are so many variables I think everybody has to find what works for them and their truck and go with it.

Jona Gold.
My stock dmf was perfect the installer said where I had my seeping rear main fixed. That was at 37K,the camper, 34"tires and Smarty on sw#3 at the time. The guy recommended a Valeo which was smooth but slipped at 12K.
You posted the part# and where you obtained it.
Would you mind posting that again?
The new LuK might be the ones they're putting in the 4th gens.
My OKHD is only rated to 900 ft lbs.
Thanks

I agree, technically clutch ratings should only be for torque. HP does not apply.
(A good example would be a dinky little clutch that can hold 500 HP on an LS7, that same clutch could never hold the torque produced by a cummins at 500horse.)

Put in another call to Southbend today and left another message. still no call back.

Sorry, without attribution, I don't swallow this at all.

DMF's are for NVH issues, not transmission survival.

I am happy the stock clutch is working for you, but not having a DMF flywheel will not kill a transmission.

And yea, I am a Mechanical Engineer by trade.

LuK kit is 05-182, currently $530 Amazon primed to your door- and that includes the clutch AND the DMF (plus pilot and t/o bearing- it's the full kit).

From the LuK website here: LuK Germany | Products | Dual Mass Flywheel (DMF)

LuK found that while they originally went for human comforts, the results of installing a DMF reduced load on the transmission and "A favorable side effect is that the transmission is easier to shift because of the low mass to be synchronized, and there is less synchronization wear."

So according to LuK engineers, the DMF does protect the transmission. If the G56 was designed with this in mind, running it without is indeed harmful.

TDR had an "ask the engineer" segment and the smf conversion issue came up. Their engineers concluded that the conversion wouldn't harm the trans either and that the dmf was included to enhance the consumer experience.
That goes against my sensibilities though.
I believe that to return to a stock clutch,an adapter plate and other items are necessary in addition.

patdaly,
I agree mostly, but the noise my 07 is making without the DMF, is 10x worse than my 92(never had a DMF). WAY higher Db, and way more sensitive to the load/RPM thresholds that cause it. (but the same root cause and result is present).
It's absolutely the result of frequency resonance. The natural frequencies inside the G56 seem pretty low, probably a lot lower than the NV4500 in my 92. Once you get up above 1500 RPM, you are ok, (Input frequency is >> than Fn)

Now, the DMF was definitely added for NVH reasons. No question. (I hate the fact that my truck has added cost and complexity just to be quiet). But, when they did that, the DMF allowed them to get away with lower natural frequency structures elsewhere(the tranny)(probably saving some dollars and pounds).

I dont mind noise for the sake of noise, but this sound just kind of makes you cringe. This type of resonance never happens on industrial equipment where NVH criteria dont exist. And if you did hear your backhoe make a sound like this, you would start planning some maintenance. just sayin.