After replacing my clutch a couple weeks ago, I thought I'd share in case it helps someone out. When I was searching for info after I began to have issues, I didnít find much info on my specifics.
I bought this truck used and was told it had a South Bend dual disk. I'd had three other manual trans Cummins trucks with standard clutches, and I found this one was tricky to learn to drive smoothly. It seemed to act like a switch, on or off, not much in between, and was pretty noisy at idle and chirped a bit taking off in 2nd. Also it began to grab at the top of the pedal travel. Since I had never driven a clutch like this before, I accepted it as normal for its' type, and was happy that it held the power without slipping.
That was ďnormalĒ for over a year and ~25K miles since I bought the truck. Then I was backing into the pole barn like every night and heard something let loose and fly around the bellhousing a few times. Yikes. That sinking feeling came over me as I tried to figure out what had happened. I looked underneath and couldn't tell anything, so I moved it back and forth a few times. Everything seemed OK. I drove it a few days, paying extra attention for anything unusual. It did seem noisier, but worst of all, I was able to slip it for the first time, full throttle in 6th.
I still don't know if it was related, but I had put it on the dyno this year at Scheidís Extravaganza. It didn't seem to show any ill effects from that, as I drove it two hours home, and daily since. Honestly, I can be harder on it at times than the dyno operator was.
After the slip, it was clearly time to replace it. I called South Bend Clutch and was truly impressed with their customer service. Since I am only a two-hour drive from them, they said to send them some pics once I got it apart and they'd have a kit ready for me to pick up. They asked for pics to verify which clutch it had, and that it was truly their clutch. I pulled the trans. Turned out it was a SDD3250-G, and I found the source of that noise I heard backing into the barn - the four pins for the floater plate lying in the bottom of the bellhousing.
I went to Mishawaka the next morning to pick up the replacement, which they had sitting by the door ready to go as promised. Also bought their cast iron input bearing retainer that the throwout bearing rides on, as the stock sheet metal piece was worn. They explained that the clutch design had been improved to have those pins bolted in from the back of the flywheel - not just pressed in.
Got it back together that evening. Itís a whole different truck now! Pedal feel and grab is much more manageable Ė feels like a stocker in comparison. The grab begins a bit off the floor now instead of at the top of the pedal travel. There is hardly any clutch noise at idle now, and there is so much less vibration Ė Iím sure when the pins came out, it threw off the flywheel balance. Backing up is smoother too, but havenít towed yet, so I canít comment on backing a trailer.
It is still in the break-in period, so I havenít given it full power yet, but Iím confident it will hold.
So in the end, I believe it was a combination of the clutch being worn after lots of use, then of course the pins letting go, and also the improvements in design and clutch materials that makes such a marked difference in my clutch. Here are a few pics from the replacement.