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Exedy Mach 600 clutch and Billet Flywheel Review (S197 Mustang)

This is a bit overdue (okay, long overdue) but I figured it's better late than never. If you're following me on Instagram or Facebook, you already know that I had to replace my clutch in 2018. It wasn't so much because the clutch failed. It was actually the clutch slave cylinder. Why would I need to replace the clutch if my slave cylinder went? Well, Ford had the genius idea of putting the slave cylinder inside the transmission. Ok, this isn't entirely fair. Putting my engineer hat on, I can see how this makes sense. If you put the slave cylinder in, it's outside of the elements and should theoretically last longer. Unfortunately, Ford should have invested in a better slave cylinder for this to be a great idea, not one that can't make it past 22,500 miles (36,000 kms), albeit with track use - which probably exacerbates the problem because of the additional heat and higher temps. But I digress.

At any rate, the slave cylinder went. Most people would replace the clutch in this case since you have to tear into the trans anyway. I was certainly considering it, but my decision became a lot easier when I got a call from the shop saying that the slave cylinder bent and damaged the clutch pressure plate. I needed a new clutch. After a lot of shopping around to find vendors and figure out which clutch to buy, the awesome folk at Team Beefcake Racing put together a great deal for me for a new Exedy Mach 600 (stage 4) clutch, Exedy billet flywheel (factory one doesn't fit), and a new hydraulic slave cylinder.

The clutch is the highest spec single-disc for this car and is good for 734 lb-ft at the flywheel, so there's massive room to grow and far more than I'd ever have since the car will always stay naturally aspirated. I pulled the trigger. An excruciating 500 break-in miles followed, which required no high rpm shifting, quick shifting, or hard launches according to Exedy. I wasn't sure what constitutes "high rpm", but I considered roughly middle of the range (i.e. 4,000 rpm) to be the threshold for high rpm. That took a great deal of self control, but once that passed, the Boss was finally unleashed again.

My first impression was driving away from the shop and it wasn't too great. There are two issues, both affecting day-to-day driveability. First was with the clutch. Compared to the OEM clutch, the engagement point is lower, the range of modulation is narrower, and clutch take-up is more abrupt. In other words, it's more tricky to take-off or drive in stop-and-go traffic smoothly. I more or less expected that, but I was hoping it would be less pronounced.

The second issue was with the flywheel. It isn't supposed to be a lightweight flywheel, but I'm assuming it is a little lighter. With the OEM clutch and flywheel, you could gently let off the clutch pedal and the car would smoothly takeoff without even giving any gas (I always smoothly rolled in the gas, regardless). With the new flywheel, if you tried to do that, there would be a noticeable shudder followed by vibrations and almost bucking if you didn't start rolling in the power. I also had to keep rpms higher, having to take off above 1,000 rpm or so, otherwise, taking off wasn't smooth or pleasant.

I think the abrupt clutch take up exaggerates the effect of the lighter flywheel and vice versa. But those are issues you'd expect with a higher performance clutch and flywheel. On the plus side, the clutch effort was barely more than stock and clutch feel was great, especially considering the high torque carrying capacity. Overall, I wasn't really disappointed with the clutch. I figured I'd hold my judgement until my first track day. I actually had to go on a couple of drives to accelerate break-in and go 500 miles before the first track day. I arrived on the track after a little over 520 miles following the break-in, so it was close, but I made it. The moment of truth was here and it was finally time to find out how the clutch and flywheel perform where they belong; on track.

2012 Boss 302 at Atlantic Motorsport Park - Andrew R. M. ©

Hole-eeee SMOKES! Ok, a little background first. If you aren't too familiar with pushing a late model Mustang GT or Boss 302, there's a known limitation referred to as "shift lockout". It happens because the clutch is not the best clutch in the world (disengagement is not excellent at high rpms) combined with a remote transmission shifter. The remote shifter in the car is not directly mounted on the transmission, rather, it's mounted to the body/chassis. And because Ford has certain standards for in-car NVH for this car, there are a couple of bushings that have no business being in a car like the Boss 302.

That means that when you're on track and pushing the car, the engine and transmission are moving/deflecting as a result of torque and g-forces but the shifter isn't following in step with every motion. This, combined with the mediocre clutch, result in being locked out of the gear when you are trying a high rpm shift. It's very frustrating and some people have ruined their synchros as a result. I learned to drive around it (delaying the shifts slightly if the car isn't going straight seems to work the vast majority of the time).

2012 Boss 302 at Atlantic Motorsport Park - Kevin Doubleday ©

With the new clutch, though, there's no such need. Shifting can be faster and feels SO much more satisfying. This was most noticeable in the 2 to 3 shift between T2 and T3 on our track, which is uphill, very slightly cambered, and never completely straightens out from exit of T2 to entry of T3. All of this resulted in plenty of missed 2 to 3 shifts if you tried to hurry it, so I stopped. With the new clutch, it was a breathe. I missed it once or twice on the first day immediately following the 500-mile break-in period. In the 13 track days since (including 3 Time Attacks), I've never missed a shift. And the narrow range of modulation works perfectly on track and imparts a feeling that the clutch is much more precise (which it is).

The small downsides are a very small price to pay for a (much) higher performing clutch. It performs flawlessly on track, but is still light and smooth on the street. There is no chatter and once you get used to it, you can easily perfect smooth take-offs. If the car is going to serve double duty for daily driving that you are always run into grid-lock stop-and-go type traffic, you might get annoyed by it. Otherwise, it'll be excellent. Overall, I couldn't be happier with the clutch and would happily recommend it to others.

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