Curing What Ails A 2005 Ram With A Twin-Disc Clutch

Diesel trucks with manual transmissions are hard to beat, especially when it comes to towing. Though there are some excellent automatic transmissions out there, many diesel owners still prefer a stick on the floor to a shifter on the column. Even though manual transmissions have been around for a long time, the good news for these diehard stick fans is that technology continues to evolve, both in the transmissions themselves and the critical link between them and the engine. There’s a lot of new technology in clutches targeted towards the diesel truck market that address the concerns of both the diehard stick crowd and performance enthusiasts, but it all boils down to how to best get the power to the ground.

With the big power that modern diesels are putting down these days, especially once a few aftermarket modifications are added to the mix, it’s easy to understand why most stock clutches aren’t up to the task. The reliability issues of the dual-mass flywheels on Cummins-equipped engines aside, strap a big load to a mildly warmed over Cummins and you have a recipe for clutch issues. Some people gravitate toward a multi-disc system that can handle the extra power and heavy loads, but many of the multi-disc clutches on the market introduce quirks that make the truck a hassle to drive every day, like rough engagement, lots of noise, and other problems. Enter Centerforce with the Diesel Twin, a multi-disc clutch solution, which provides the superior holding power of a multi-disc clutch (up to 1,700 lb-ft) and the everyday drivability of a single disc.

We traveled to H&H Diesel Performance in Dewey, Arizona, where we had the opportunity to watch a 2005 Ram get the ultimate solution to rough shifting problems and a major upgrade in clutch holding power all at the same time. We didn’t have the opportunity to witness the drivability problems the truck had when it came in, but we did drive the truck once the repairs were complete. We can honestly say the clutch “feel” of the Centerforce twin-disc system was exactly as it should have been: it felt no different than a stock clutch when it came to shifting, engagement or anything else that would indicate that the truck was now equipped with a multi-disc clutch. Check out what it took to fix what ailed this Ram and its shifting problems once and for all. DW

1 The subject of our clutch upgrade was a 2005 Ram 3500 4×4 dually. The owner of the truck uses it to haul equipment for his glass company, so the truck gets used hard and rarely moves without a trailer attached to it and heavy stuff in the bed. This truck also has some mild performance upgrades. The truck was having some shifting problems that gradually got worse. The owner wisely chose to take the truck to H&H Diesel Performance in Dewey, Arizona, one of the better-known diesel shops in the region. H&H handled the diagnosis and wrenching duties for this article.
2 Truck owner Mike Reidhead reported difficulty in shifting gears. Initially thinking the problem was in the clutch, the techs at H&H tore down the truck and discovered that the clutch, while showing some wear, was in good shape. Closer inspection revealed problems with the six-speed G56 transmission. The tranny was sent out to Red’s Transmissions in Buckeye, Arizona, for a rebuild and came back a few days later looking better than new. Though the exact cause of the transmission problems was undetermined, the synchros were heavily worn and there were indications that the tranny had been run low on fluid at some point in its life. H&H recommends checking the input shaft carefully for excessive play, which is indicative of front transmission bearing problems.
3 The truck already had an aftermarket clutch due to prior issues with the factory dual mass flywheel, but it had a fair amount of miles on it. Though it’s always a tough call to replace a clutch that’s within specifications, the owner wisely chose to go ahead and replace it. Bill Hughes from H&H handled final removal of the clutch and flywheel assembly, as well as the rest of the wrench-spinning on the project.
4 The multi-disc Diesel Twin clutch from Centerforce is a pretty serious unit that’s capable of handling up to 1,700 lb-ft of torque. The system consists of a new one-piece flywheel that replaces the problematic stock dual-mass flywheel, a pair of clutch discs, floater, pressure plate, and a new slave and clutch master cylinder. Multi-disc clutches are known for tremendous holding power, but they also have a reputation for being noisy, having rough engagement, and needing a large amount of pedal effort. Centerforce has gone to great lengths to overcome all the negative characteristics of a traditional multi-disc clutch in order to make a clutch with excellent holding power that acts just like an ordinary clutch, making it an excellent choice for a hopped-up daily driver or one that spends most of its time hauling heavy stuff.
5 One of the sources of noise on a multi-disc clutch is the drive floater tends to rattle against the studs or pins on the flywheel during engagement. One of the tricks Centerforce uses to solve this is a proprietary spring-loaded bushing arrangement on the floater disc that engages four pins on the flywheel (the small pin between the larger ones in the center of this photo). This bushing takes up the small amount of slack between the pins and results in smooth engagement with none of the traditional rattle. Also note the grooves and holes machined into the floater, which helps dissipate heat.
6 Another trick that Centerforce uses to combat noise and rough engagement is a dual-spring hub in the clutch discs. Note the two light springs in the center hub of the disc along with the four much thicker, heavier ones. The G56 transmission is known for a lot of gear noise, and this dual spring arrangement helps absorb much of the noise while assisting with a smoother, more gradual engagement of the clutch. The clutch material itself is also exclusive and something that Centerforce manufactures in-house. These and other tricks results in a clutch that has the holding power of a multi-disc system with the drivability of a more traditional clutch.
7 No internal transmission modifications are necessary to handle the increased thickness of the Centerforce Diesel Twin system, but there’s one small modification needed for proper clutch fork geometry. Centerforce recommends removing the OE flat washer behind the fork pivot, then install the new throw-out bearing supplied on the original clutch fork. A new throw-out bearing should be a part of any clutch replacement, whether it’s supplied with the new clutch or not. Pay close attention to the instructions for installing the throw-out bearing; improper installation will result in a growling noise when the clutch pedal is depressed.
8 As mentioned earlier, this truck had already been upgraded with an aftermarket flywheel and clutch to replace the troublesome dual-mass system that the factory uses. Still, the Centerforce kit incorporates a new flywheel that must be used with the Diesel Twin assembly, so Hughes removed the old one. Keep a hand on the flywheel during flywheel removal, as it’s heavy enough to do some serious damage to feet and/or concrete if it falls off!
9 Hughes recommends inspecting the rear main seal closely once the flywheel is removed. They have been known to get pushed out if the harmonic balancer is worn out, and if there’s any sign of leakage, the time to address it is NOW. A new rear main now won’t add much to the repair bill, and a leaky rear main will destroy a new clutch assembly. Fortunately this truck’s rear main was perfect, even with more than 100,000 miles on the engine.
10 The Centerforce flywheel comes preassembled with all of the necessary pins and spacers pre-installed and ready to go. All of the hardware is included and it’s all genuine ARP fasteners. Hughes installed the new Centerforce flywheel on the crank and torqued it to 105 ft-lb. Note the trick flywheel holding tool that he used, though a second helper holding the crank bolt will suffice if doing the install at home.
11 Everything is pre-assembled with the Centerforce kit, but there’s some assembly required when installing it in the truck. Pay close attention to the clutch discs, because the discs are not only side-specific, but position-specific. Centerforce labels everything to eliminate confusion.
12 Pay close attention to the labels and arrangement of the clutch discs and the floater disc during assembly. Some of the parts look very much alike, so double-check your work, as Hughes did, every step of the way. Note the clutch alignment tool, which was also included with the Diesel Twin. This is a nice touch, as it saves having to track one down for the installation.
13 After both positioning the floater disc between both clutch discs with all proper sides facing one another, the last step is installing the pressure plate. It’s critical that the pressure plate be torqued properly to 35 ft-lb using the supplied fasteners so that the clutch will work properly. It’s quite an assembly, so be sure that the pilot tool is easy to remove when the clutch is torqued to spec.
14 As a final check, make sure the paint marks line up on the flywheel, floater disc, and pressure plate. Centerforce balances the entire clutch assembly as one unit and then marks the individual components accordingly. This is one more step to ensure that noise and troublesome engagement are eliminated.
15 It’s impossible to show all of the tricks that Centerforce incorporates into the pressure plate to further counteract the traditional complaints of a multi-disc clutch system, but there are several. From the unique use of ball bearings to enhance both smooth engagement and clamping force to the more traditional (for Centerforce) weights positioned on the fingers of the pressure plate, they have brought more than 30 years of experience to bear on this new system. Note how the weights on the pressure plate are positioned further out on the fingers than they would be on a traditional gas engine; this is to compensate for the slower rpm of a diesel, so the weights will come into play at the lower rpm of the Cummins engine compared to a gas engine. Suffice it to say, a lot of technology went into the Diesel Twin system knowing that diesel customers were going to push the clutch to its limits.
16 Two other slight modifications are needed with the Centerforce system, and both are included: a small spacer for the starter and a replacement clutch hydraulic system. The spacer for the starter is a bolt-in affair. The thicker assembly and the vastly different engagement timing of the twin-disc system dictates the use of the supplied clutch master and slave cylinder. Do not disassemble the clutch hydraulics for installation; it’s pre-bled and must be installed as one unit. Don’t worry about replacement parts, though; everything is genuine Mopar.
17 To demonstrate just how easy the hydraulics swap is, the clutch master cylinder installation doesn’t even require a wrench. Once disconnected from the pedal, a quarter turn counterclockwise will allow the master cylinder to be separated from its mounting bracket and the new one can be installed in its place using the same mounting bracket on the firewall. Fish the slave cylinder and plastic line carefully down the driver-side fenderwell and use caution to avoid damaging the line. The slave cylinder installation on the tranny is also an R&R procedure. The hydraulic system should not need to be bled under normal circumstances.
18 With the clutch installation done, it’s a simple matter of bolting everything back up in the reverse order of removal. Depending on the situation and the equipment available, it may be easiest to separate the transmission from the transfer case and install them both individually, as the assembly can get awkward. Hughes recommends installing the tranny and t-case individually. Even with the tranny by itself, it took some maneuvering to get the tranny seated against the back of the engine.
19 One small bit of controversy was uncovered in the research for this article. According to Centerforce. Dodge recommends full synthetic ATF+4 oil for this application. Mercedes, which manufactures the transmission, recommends 75w90 gear oil. Plus, using the fill plug position for the transmission can cause the tranny to be “filled” half a quart below the recommended capacity for both companies. Further research is needed at the time of this writing, but for this job ATF+4 at the OE-specified quantity was used. The truck used for this article needed a transmission rebuild at around 120,000 miles despite being serviced regularly by the current owner (he purchased it used), and the tranny shop reported both heavy synchro wear and suggestions of the transmission being run low on oil in its past.
20 The last step in the installation process is reassembling the shift tower and the shifter. The shift tower installs easily as long as the transmission is in neutral, and the stick is a simple two-bolt affair. Hughes spent more time reassembling the console than the shifter itself. A test-drive after installation revealed a truck that shifted just like one with a regular clutch. Engagement was progressive, easy, and there weren’t any funny noises.


H&H Diesel Performance

Red’s Transmissions

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