If you've ever had the misfortune of driving a modified Corvette with a terrible clutch, you know all too well how badly it can affect the entire driving experience. And we're not talking about a stock unit that's slipping—we're talking about a calf-straining beast that acts more like an on/off switch than a smoothly modulating unit.
Slowly leaving a parking lot? Here, let me chatter twice, bog, and then shut off on you. Trying to slip the clutch a bit at the track? Best I can do is full engagement right off the floor and an embarrassing 2.6-second 60-foot time. Yes, a bad clutch can ruin everything.
Do I sound bitter? Maybe, but I've had the displeasure of driving horrible clutches in a variety of cars for years. Some grabbed right off the floor, some waited until the very tippy top of the pedal travel, and some just did whatever they liked whenever they felt like it. Too grabby, too "slippy," too firm, too soft…it can be hard to find one that's just right, and considering that installation involves removing the entire driveline on a fifth- or sixth-generation Vette, it's important to make the right choice the first time.
So, when Quarter Master released its new single-disc Optimum-SR clutch package for the C5 (a dual-disc unit is also available), we had a decision to make: Stick with an old favorite, or try the new kid on the block?
On paper, the stats are impressive. Featuring billet construction, the Optimum-SR 10.4-inch single weighs 50 percent less than a factory LS6 clutch and can hold up to 700 hp and 500 lb-ft of torque. According to the company, the kit's lighter weight "creates reduced Moment of Inertia (MOI), allowing the engine to rev and de-rev quicker than a stock OE unit." A sprung hub and proprietary spring technology are said to allow for a higher clamp load while still offering excellent power modulation and release force.
Finally, the entire clutch is rebuildable, should it need service down the road, which can save you money in the long run. At $2,145, it's not the cheapest offering on the market, but, as is often the case with aftermarket performance parts, you get what you pay for in the clutch world.
Of course the real question is, how does it drive on the street? Our test car, a 445rwhp '03 Corvette Z06, rolled into the shop at AntiVenom in Seffner, Florida, running a thrice-replaced factory LS6 clutch. The pedal feel was smooth as silk, and engagement was good, but in the upper-rpm range (6,000-plus), the car would no longer shift into the next gear.
With the Quarter Master unit installed, our immediate thought was that something in the hydraulic system must be wrong. The pedal was so soft, so velvety, that we couldn't actually believe the clutch was engaging. A couple of tests proved everything was working correctly, and the pedal was in fact just that easy! It was like a stock clutch right off the assembly line: silky smooth, without any intense pedal effort.
Clutch in, drop it in gear, and we're off. Chatter? None. Bucking? None. Driveline noise? Nope. Quicker revs? Absolutely. High-rpm shifting problems? Gone! Smiles? All around. The Optimum-SR really did feel like a factory unit (much like a stock LS7, if you've driven one), but it allowed the engine to rev quicker and the clutch to engage faster. Even if you're a clutch cynic like me, this is one billet beauty that will keep you smiling.
01 The Quarter Master Optimum-SR single-disc clutch features billet construction with proprietary spring technology, allowing it to hold up to 500 lb-ft of torque. It’s fully rebuildable, 50 percent lighter than a factory unit, and provides a stock pedal feel. The only hard part is getting it installed!
02 While it’s possible to do a clutch job in your garage, the project will most likely consume a long weekend, even with access to a lift and transmission jack. AntiVenom, meanwhile, had us back on the road in less than one day. First step: Remove the FAST intake manifold to allow room for the engine to tilt back.
03 The entire exhaust system drops out next, including the long-tube headers, “X” crossover pipe, and muffler sections. Don’t forget to remove the oxygen sensors before dropping the headers out of the way.
04 Inside the car, you’ll need to remove the shifter assembly. This will allow the torque-tube assembly to drop completely from the underside of the car.
05 All the way out back, it’s time to start disassembling the rear suspension. This will enable you to drop the rear cradle out of the way to remove the transmission and differential. Did we mention how much work is involved with installing a new clutch yet?
06 A normal person should use a trans jack to remove the stock C5 rear-suspension cradle, but Kyle Miller is a monster, so he just pulled it out by hand. Safety first!
07 Next, with a trans jack holding the rear assembly and torque tube in place, it’s time to remove the axles from the differential housing. If you’ve made it this far, you’re almost halfway there.
08 Don’t forget to unhook the slave-cylinder line, which you can find tucked up behind the engine block, near the oil filter. This is much easier with the correct release tool, which you might be able to source at your local parts store.
09 Finally, it’s time to drop the rear assembly and torque tube out of the C5 chassis. Balance is critical here, even though the torque tube is quite light. Remember that the slave cylinder is still installed up front, so make sure it doesn’t get hung up on the bellhousing on the way out.
10 The six bolts holding the clutch assembly on the factory flywheel should be removed with an impact wrench if possible. Rotating the flywheel to access them should be done with a job-specific flywheel tool, but a flat pry bar will work in a pinch.
11 With the clutch out of the way, you can remove the six flywheel bolts before dropping the flywheel out of the bellhousing. Be careful, as it’s not light.
12 Installing the new Quarter Master Optimum-SR begins with disassembling the new unit, which is as simple as removing the eight perimeter bolts that hold the billet cover to the lightweight flywheel. With the cover removed, you can see the sealed spring hub—a nice touch.
13 The vented and grooved floater plate comes out next. It bolts in place with a “strap drive” to provide quieter operation and reduced noise, vibration, and harshness.
14 Built from “high-grade OE-type material,” the 10.4-inch clutch disc (left) can handle up to 700 hp while still engaging like a stocker. You can see just how much smaller the disc is compared with an LS6 unit (right).
15 Next up is the flywheel, which bolts on to the engine using six provided bolts. It’s much lighter than the stock unit, so sliding it in place was a breeze.
16 With the flywheel bolted down and torqued to spec, Miller dropped the clutch disc in place, followed by the strap-drive floater. Four bolts hold the straps to the flywheel.
17 The billet cover-and-spring assembly goes on last and is held to the flywheel using eight bolts. It’s a shame you have to hide the anodized cover—it just looks so cool!
18a Quarter Master sent us a new slave cylinder to use with the new clutch. We recommend changing yours out "while you're in there," since it's a quick and easy swap (and costs very little compared with pulling out the driveline again).
18b Quarter Master sent us a new slave cylinder to use with the new clutch. We recommend changing yours out "while you're in there," since it's a quick and easy swap (and costs very little compared with pulling out the driveline again).
19 Next step: Put everything back together. Torque tube, transmission, differential assembly, axles, suspension, rear cradle, exhaust parts, shifter, intake manifold—all of it must go back together before you can get back on the road. For AntiVenom, this is the easy part.
20a The new slave cylinder does require changing out a fitting on the master. First, remove the factory fitting, which is held in place by a roll pin, then slide the Quarter Master–supplied fitting in place and reinstall the pin.
20b The new slave cylinder does require changing out a fitting on the master. First, remove the factory fitting, which is held in place by a roll pin, then slide the Quarter Master–supplied fitting in place and reinstall the pin.
21 Finally, it’s time to refill the clutch hydraulic system and do a little bleeding, preferably using Quarter Master Race Clutch Hydraulic Fluid. A little gravity bleed, followed by a pump-and-bleed session, was all it took. And just like that, we were back on the road with a lighter, faster, stronger clutch. vette