The Ford Mustang has been a popular choice for enthusiasts since its introduction in 1964, and for good reason: it’s an effective and affordable blend of sporty capability and every day practicality.
Right now the Mustang’s performance prowess is the best it’s ever been from the factory, and models like the 2012-2013 Mustang Boss 302 proved that Ford has the engineering mettle to bring world-class road course capability to the masses. But while the Boss 302 significantly dialed up the Mustang’s proclivity for corner carving and track day capability, there will always be those who want a bit more.
Heintz had a very specific vision for his Mustang Boss 302 - a car that was as at home whipping around Turn 9 at Big Willow as it was handling the daily commute. While his Kognition Racing S197 Wing kit and Built 2 Apex front splitter are motorsport-level aero pieces, this car definitely still spends plenty of time on the street, so retaining drivability has been at the forefront of Henitz’s mind whenever selecting mods. Image: Eric Broadfoot
My vision was to build the perfect daily-driven car that can go to the track and take on cars out of its class. - Michael Heintz
Michael Heintz is one of those people. “My vision was to build the perfect daily-driven car that can go to the track and take on cars out of its class,” he explained. “I use this car as a daily-driven canyon carver, and I also take it out to autocross events and local track days.” But, as Heintz added performance to his Mustang, the additional capability started showing some of the car’s weak points, which included the OEM clutch.
To beef up the gearbox without sacrificing street drivability, he enlisted the help of the folks at McLeod Racing. Its Street Extreme clutch for the 2011-2014 5.0-liter Mustangs (PN 75353) is designed specifically for cars like his that see a significant amount of track time, but need to be steerable for daily driving duty. Voss Performance in Placentia, California handled all the install duties for Heintz.
Heintz has suffered multiple failures with the OEM MT-82 gearbox. This McLeod clutch is step one of a two part solution he’s trying which also includes a new MGW Race Spec shifter. The new clutch and shifter combined should help resolve the high RPM shifting issues that plague the stock clutch, while the MGW shifter will enhance shifting precision. You’ll be able to read about the install of that shifter in an upcoming tech article as well. Photo courtesy of Eric Broadfoot.
Along with an assortment of suspension components fromMaximum Motorsportsand a set of KW Clubsport coilovers, Heintz’s Boss Mustang also has a few powertrain components from Ford Racing, including a set ofCobra Jet camsthat contribute to the Mustang’s new 8,200 rpm redline – a substantial bump from the stock peak of 7,500.
“I went through two OEM MT82 six-speed manual transmissions because the clutch wouldn’t disengage at high RPM,” Heintz said. “After installing all those parts, when I would go to shift the car at anything over 7,500 rpm I was constantly concerned the transmission was going to blow up.” That’s generally not good for driver confidence – or lap times, for that matter – but the Street Extreme clutch is designed specifically for that kind of abuse.
Before Heintz had a chance to send another gearbox to the boneyard he thought it would be prudent to get a more substantial clutch in the mix, one with higher heat tolerance and durability that was designed to maintain street-friendly driving manners. Fortunately, McLeod Racing makes a clutch for this specific purpose with its Street Extreme series.
“This is truly a dual purpose clutch,” says Bob Scheid of McLeod Racing. “We’ve made specific design choices that allow this clutch to be street-friendly while substantially bumping up its holding power in a track setting.”
Recommended for cars with up to 700 crank horsepower running on DOT-legal tires, the Street Extreme clutch uses a high clamp load pressure plate and dual face ceramic disc that provides significantly more heat resistance and durability than the stock clutch, but also manages to retain smooth engagement and the stock pedal pressure while doing so. The result is a clutch that’s far stronger than the OEM unit while keeping all of the drivability attributes of the stock clutch.
“The ceramic-lined disc we use is different than most,” explains Scheid. “Many clutches like these have abrupt engagement because of the reinforced design, but that’s something we’ve worked to address while making sure the clutch can handle the rigors of track duty.”
With that pesky transmission out of the way we could then get at the clutch to remove the stock unit and replace it with the one from McLeod. The stock clutch uses an organic lining material that's designed to provide some slip. That equates to good street driving manners but it can cause serious problems out on the track when you're at 10/10ths, especially if your car is modified beyond stock specifications.
Further bolstering the clutch’s strength is its ductile casting, which enhances overall durability, as well as additional straps versus the stock unit. “Straps are kind of a weak point for most clutches,” Scheid explained. “Adding extra straps helps prevent bending and torquing that can potentially harm the pressure plate.”
The McLeod clutch features a ceramic disc lining designed to tolerate heat more effectively than the stock lining, but unlike many of its ceramic counterparts, this one is designed to provide smooth engagement. That’s not a high priority on race-only clutches, but since the Street Extreme is intended for track-focused street cars, this strikes an effective balance between on-track durability and street-friendly behavior that isn’t “grabby.”
The heavier diaphragm springs makes the clutch easier to shift at higher RPM, and extra straps on the casting makes the clutch much more durable. When you put that shock on them at high RPM, it would take much more to damage the clutch. - Bob Scheid, McLeod Racing
But what about pedal pressure? While a stiff clutch might be tolerable in a purpose-built race car, street cars that need to contend with traffic on a regular basis can become torturous when you’re in bumper-to-bumper congestion.
“The clutch diaphragm determines pedal pressure,” Scheid tells us. ”We purposely chose a diaphragm design that would offer similar resistance to the OEM piece. I have this same clutch in my M3, and in terms of pedal pressure, you’d swear it was the stock clutch.” But out on the track, the enhanced strength and heat resistance translate to a clutch that’s designed to take this level of abuse.
“The heavier diaphragm springs makes the clutch easier to shift at higher RPM, and extra straps on the casting makes the clutch much more durable. When you put that shock on them at high RPM, it would take much more to damage the clutch,” he added.
McLeod Racing says that there are essentially three ways you can increase the holding power of a clutch: increase the clutch pressure, which would not work in this application because it increases pedal pressure. You can also add a more aggressive disc, but that will negatively affect street driving behavior. The third way is by increasing the surface area of the discs. But because you can only make the diameter so large, McLeod Racing opted for a dual face disc design, effectively doubling the surface area. By doing so, McLeod makes its clutches capable of producing serious holding power while maintaining stock-like pedal effort.
Heintz’s impressions after installing the McLeod clutch in his Mustang echo Scheid’s. “The pedal feels very similar to stock which is what I wanted for a daily-driven car,” Heintz reported. “I’m on the 405 and 91 freeway in stop-and-go traffic a lot, and I’ve never regretted my choice. From a stop, I can drive the car like it’s a stock clutch, but when I’m driving aggressively the clutch bites hard like it should.”
With the clutch all buttoned up, the gearbox can be hooked up to the drivetrain again. While he won’t be able to see the sweet red paint job of the McLeod Racing clutch once everything is put back together, Heintz will certainly get a benefit from it in both increased on-track performance and a lack of grenaded transmissions piling up in his garage.
The Street Extreme clutch kit comes with everything needed need to make the switch – the pilot tool, throw out bearing, and pressure plate bolts are all included (where applicable). It’s available in standard 10-spine for use with stock 05-10 mod motor Mustangs (and all the way back to Fox bodies), 23-spline for 2011-14 Mustang 5.0, and 26-spine for Tremec gearboxes.
McLeod Racing also offers several other flavors of streetable clutches for Mustangs, ranging from the Street Level kit, which is designed for cars with mild bolt-on modifications and offers a solid value for builders on a budget, to the Super Street Pro, which is recommended for cars with up to 550 horsepower.
McLeod Racing says it encourages owners to go through a proper breaking-in procedure before doing any intense driving on the street or at the track. With a new clutch installed, it’s important to be sure the clutch is grabbing across the full area of the disc — within a few engagements it should be obvious whether everything is copacetic or there’s trouble afoot. McLeod recommends about 500 miles of non-highway driving in order to break in the disc surfaces.