Picking the Right Clutch for Your Manual Transmission

Diesel Performance Parts, Dodge Cummins, Ford Powerstroke, GM Duramax, Products, Tips and TricksTags

The exact production numbers are about as hard to tabulate as the Iowa Caucus was this February, but approximately 97% of all diesel pickups sold in the US over the last 20 years left the factory with an automatic transmission. Its pretty clear American truck buyers prefer an automatic more and more, and due to shrinking demand, you can’t even buy a stick shift diesel if you want to. 2018 was the last year you could get a manual transmission, and the last man standing was the G56 6-speed found in the Ram heavy-duty. A few years before that, Ford quit offering their manual transmission option at the same time they made a body style update and switched to the 6.7 Powerstroke in 2011. GM was the first to give up on the three-pedal trucks 2 years before Ford in 2006, when they dropped the ZF-6 option from their lineup on the LBZ.

For the average truck buyer, the thought of owning a manual transmission must be absurd, as an automatic is easier to operate, simpler to drive in traffic, and modern 6 and 10-speed autos offer a wider spread of gear ratios for easy take-off when fully loaded while keeping a low RPM when cruising at highway speeds. Another thing an automatic transmission is great for is quick acceleration, because you can shift through the gears without letting off the throttle. When it comes to drag racing with a manual transmission, every time you let off the skinny pedal to shift you will lose a bit of boost pressure, and it will take a second for the turbo to re-spool once you get back into the throttle. A driver might choose a manual transmission for different reasons, and more than likely they’ll have something to do with hauling a big trailer. Being able to keep your transmission in the gear you want has huge advantages when going up and down steeper grades, especially if you use an exhaust brake or a Load Leash to control downhill speed. Other benefits to a manual transmission include less parasitic loss, which will give a slight advantage in efficiency, and because there are fewer moving parts inside, there is less to go wrong.

The Weak Link

Even if you deliberately try to abuse your truck, there is very little chance of damaging the internal parts of most manual transmissions simply by over-powering it, but every superhero has his Kryptonite, and for the manual transmission, it’s the clutch. It’s a simple part which functions very similar to a brake pad and rotor. First there is a rotating steel disc called the flywheel, which is attached to the engine. It helps store energy with its heavier mass. The clutch disc is splined onto the input shaft of the transmission, and a pressure plate squeezes the two together to create friction much like a brake caliper. The reason a clutch is needed is to be able to disconnect power flow from the engine to the rest of the drivetrain for shifting gears or taking off from a dead stop, and the friction material needs to allow a certain amount of slipping to facilitate a smooth engagement yet be strong enough to pass all the torque produced from the engine along to the transmission. The clutch which was installed in your truck when it was new was designed around the engine’s stock power rating, and it provided smooth engagement, light pedal effort, and will generally last for many miles.

As long as you keep a stock power level, your original clutch will work for a long time, but as we all know, leaving a truck stock usually isn’t an option. It’s all too easy to throw on a tuner, exhaust, and intake, and have an extra 300 pounds of torque available under your right foot, but that much more power can easily push any stock clutch past its limit. There are a ton of aftermarket clutches which can hold up to nearly every power level imaginable, but with so many styles and options of friction material, it can be hard to decide which one is right for your truck.

If you are shopping for a clutch, it might be tempting to pick the baddest clutch money can buy, and you’d expect it to be the last clutch you ever need. The reality is that can be detrimental to your driving experience. Remember our last post on drivability modifications for an automatic transmission? The same pitfalls and gotchas exist with a standard transmission, and if you don’t pick the right clutch for the job, you’ll be kicking yourself at the very least, and at the most you’ll be buying another clutch and doing the job again. Let’s get started, shall we?

Clutch Anatomy

There are three variables which determine how much torque a clutch can transfer without slipping, which are the surface area (how many square inches of friction material are in contact with the flywheel), clamping force (how hard the pressure plate squeezes), and the coefficient of friction (what it’s made out of and how grippy the material is). Most trucks leave the factory with a woven organic clutch, as it offers some of the smoothest engagement, has a high resistance to wear, and a mid level torque rating. If your stock clutch has simply worn out and you need a replacement but don’t plan to add any more horsepower, you should simply replace it with another Organic Clutch Kit. It will be extremely reliable, will provide very smooth engagement, and will work great for towing just like your stock clutch did.

Once you’ve made some of the basic performance upgrades to your truck like an intake, high flow exhaust and a hot tune, likely you’ve slipped the stock clutch a time or two. Everyone knows the feeling when you floorboard the skinny pedal and the RPMs jump up but you don’t accelerate, and that’s a clear indication your stock clutch is on borrowed time and you need to consider stepping up a notch. A Ceramic Single Disc Clutch is a move in the right direction. It’s made from a combination of materials like copper, iron, bronze, and graphite, and one of the greatest benefits to ceramic clutch material is its higher coefficient of friction. It will withstand a lot more heat than an organic clutch, without breaking down or losing grip, and generally ceramic friction discs will hold a lot more power than stock, making them desirable in performance or heavy-duty applications like towing. HOWEVER, the one thing you need to keep in mind about a ceramic disc (or any upgraded clutch for that matter) is you lose some of your silky-smooth engagement you had with an organic disc, but options like a diaphragm style pressure plate or a sprung disc can minimize any potential issues. For most truck owners, a ceramic clutch can still comfortably be used as a daily driver, but because it’s made from a harder material, it can wear out slightly quicker than an organic clutch, but it’s a small trade off to make for a clutch with increased capacity.

If you want to push your horsepower a bit further than basic bolt-ons, you’ll need to look for a material that has a higher power capacity, and next up on the list is Feramic, which is similar to Ceramic, but has a slightly different combination of ingredients. A South Bend Full Feramic Clutch has a torque rating of 1,100 lb.ft. in a single disc application, yet will still have acceptable street manners, plus, the material can still work great while hauling and towing. Organic, Ceramic, and Feramic are the most popular materials for a clutch, but there are dozens of other variations used in friction compounds, like metallic blends, Kevlar, bronze, and even graphite. It all depends on how the manufacturer wants to balance engagement, heat resistance, longevity, and of course, power capacity.

Multiple Discs

While a gripper friction disc will be able to get more power to the ground, there is still a limit to how much torque can be transferred, and even the best single disc clutch will be rated somewhere around 550 horsepower and 1,100 pounds of torque. The good (and bad) news is those numbers can easily be surpassed with a drop-in turbo upgrade or a larger set of injectors, and the next way you can increase the capacity of a clutch is to add surface area with more discs. A twin or triple disc clutch has the same exact parts as a single disc, except now there is a steel floater plates which goes between each friction disc. It might sound confusing, but just picture a Big Mac with the all-beef patties being the clutches and the buns as the flywheel, pressure plate, and floater, and you’ve got the idea. For the G56 equipped Ram, the Valair Street Triple Disc Ceramic clutch is able to hold a whopping (pun intended) 1,000 horsepower, and because it’s made with ceramic discs it will still have smooth engagement for driving on the street. In order to fit three clutch discs, two floaters, and a pressure plate all between the crankshaft and the transmission, this kit comes with a specially shaped solid flywheel which is great news because it allows you to eliminate the troublesome dual-mass flywheel which plagued the G56. There is one thing to keep in mind when you are using a multi-disc clutch: it will make some noises you may not be used to when you push in on the clutch pedal for the first time, and at first you may think something is not installed properly because it has an audible rattle. Each style of multi disc clutch will sound slightly different, and some are much louder than others, but don’t worry, its completely normal. When the pressure plate is released, the floater discs are just moving around inside the clutch assembly, and the firing pulses of the engine cause the metal discs to rattle around, and as soon as you lift your foot from the pedal, the pressure plate squeezes everything together again, stopping the noise.

The Clutch Masters dual disc clutch for G56 trucks is unique in two distinct ways. First, its built to be the exact same depth as the OEM clutch, meaning you don’t need to change the hydraulics in order to adjust the throw. Secondly, just look at that machined pressure plate! Others use a stamped steel version, which has absolutely nothing wrong with them, just the fact that the machined version looks cool!

If you can’t stand any noise at all but need more capacity than a single disc can offer, there is one more option on the market which will get the job done, and that’s the Clutch Masters Twin Disc Clutch kit. They offer both Organic and Ceramic versions for most popular transmissions, and the unique design uses small metal straps to prevent the floater plate from rattling around. The organic version is rated to hold 1,400 pounds of torque, and the ceramic option steps it up to 2,000lb.ft., and the best part is the clutch should work with your original style hydraulic throwout bearing.

What’s the Downside?

There are some pitfalls to look out for when selecting your clutch, and they can make the difference between a fun to drive truck and a rig you don’t want to drive at all. The first is the pedal feel, which is the amount of effort required by your left leg to depress the clutch pedal. In order to have a higher torque capacity, often times manufacturers use a stiffer spring in the pressure plate, and the highest capacity clutches have a rating of around 3,800 pounds of clamping force. Even with the leverage of the pedal and the power of hydraulics working in your favor, it can still require substantial effort to disengage the clutch. It might not sound like a big deal at first, but remember, you will be pushing in the clutch every time you come to a stop, change gears, or take off from a light, which can amount to hundreds to times a day. But hey, at least you don’t need to go to the gym for leg day anymore…

Once you’ve achieved a Bruce Banner physique, you might think you’re ready to drive your competition clutch in New York city traffic, but you still need to consider how quickly the clutch will grip once you ease the pedal out. The stock organic material provides a nice smooth transition, and you can easily release the clutch and get the truck moving from a dead stop with very little conscious effort. Higher performance clutches with an extreme holding power (especially metallic) are unforgiving with engagement, as they offer very little slip. Once you start to ease the pedal out, it’s like a light switch gets flipped, and a tiny movement of your leg will cause the truck to lurch ahead from a dead stop, and if you are lucky all that happens is a buck and jump as the engine tries to recover, but there’s a better chance you’ll stall the engine like a 15-year-old kid learning to drive stick for the first time.

A Dying Breed

The clutch is one area where bigger definitely isn’t better, and if you take away only one bit of advice from this discussion, it should be this: be realistic about how much power you are actually making. If your truck produces 550 horses and you have no plans to go further, stay away from the big triple disc competition style clutches, as it will be pure torture to drive. Instead, invest in a quality clutch which is rated appropriately for your rig. You will enjoy driving your manual transmission a whole lot more, which is likely one of the reasons you chose a stick shift truck in the first place. A manual transmission certainly isn’t for everyone, and they do have their drawbacks from an ease of use standpoint, especially if you sit in stop-and-go traffic, but when it comes to sporty driving and choosing your own gears, an automatic just won’t cut it.

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