Single Mass vs Dual Mass Flywheel for the Mustang GT
If you are pulling the transmission on a manual Mustang GT for a clutch job, the flywheel decision comes up fast: keep (or buy) a dual mass flywheel, or switch to a single mass unit? The answer depends on which generation GT you drive, how much power it makes, and how much gear rattle and idle vibration you are willing to live with. This guide covers how each design works, how to tell if the flywheel you have is worn, and which way to go on a street car versus a built car.
Which Mustang GT Came With Which Flywheel
The dual mass flywheel came to the Mustang GT with the 2018 refresh. According to Street Muscle, the 2018 GT six-speed "now features a new dual-mass flywheel for reduced NVH," paired with a twin-disc clutch to handle more torque and larger synchros for the first four gears. That update landed with the engine upgrade: per the sixth-generation Mustang reference on Wikipedia, the 2015-2017 GT 5.0L made 435 hp and 400 lb-ft, while the 2018 GT went to 460 hp at 7,000 rpm and 420 lb-ft at 4,250 rpm.
In practice:
- 2015-2017 GT (and earlier 5.0/4.6 manual cars): Ford's 2018 dual mass flywheel was new, so these cars are already on a conventional one-piece flywheel with a single-disc clutch. The question for them is stock weight versus a lightweight single mass.
- 2018 and later GT: factory dual mass flywheel with a twin-disc clutch. The question for these cars is whether to replace the DMF like-for-like or convert to a single mass flywheel and a matching aftermarket clutch.
How a Dual Mass Flywheel Works
A dual mass flywheel splits the flywheel into two parts. As EduMech explains, the primary mass is "attached to the crankshaft and exposed directly to engine torque pulses," and the secondary mass carries the clutch friction surface. The two are "connected by a system of arc springs and friction elements," with an internal bearing that lets them turn slightly relative to each other. Every power pulse compresses the arc springs, so the transmission input shaft sees smoother torque.
That is why a DMF car idles quietly in gear, shows little gear rattle at low rpm, and is easier to drive in traffic. The downsides are complexity, extra rotating mass, and a part with internal springs and a bearing that wears out.
Single Mass vs Dual Mass: The Trade-Offs
Motor Werke's comparison sums it up. A dual mass flywheel is "a more effective, and more complicated, solution for reducing engine vibration," but "the energy required to spin up a single-mass flywheel is much less than that of a dual-mass." They also note DMFs cannot be repaired when damaged.
| Dual Mass | Single Mass | |
|---|---|---|
| Idle / low-rpm vibration | Well damped, smooth | More vibration, can feel "jerky" at low rpm |
| Gear rattle | Minimal | Audible, especially at idle |
| Rev response | Slower, more rev hang | Quicker, less rev hang off throttle |
| Serviceability | Replace only, cannot be repaired | One-piece; simpler, lower-cost replacement |
| Best for | Stock daily driver, comfort | Modified cars, track use, high torque |
Motor Werke puts the single mass side plainly: you get "less rev hang when you take your foot off the throttle," but "more noise is created at the connection between the flywheel and clutch." For a lot of Mustang owners that sound is acceptable. For others it is the first thing they notice after the swap.
How to Tell If Your Dual Mass Flywheel Is Worn
A worn DMF usually shows up as noise, a rattle or knock at idle or on engagement, or shudder. Before condemning it, rule out other causes. LuK (Schaeffler) says in its "Common Dual Mass Flywheel issues" service bulletin that a large number of DMFs returned for noise turn out to be serviceable, and lists common look-alikes:
- Vibration from the accessory drive (removing the belt helps diagnose this)
- Worn crankshaft damper or alternator decoupler pulley
- Excessive crankshaft end float
- Input shaft or transmission bearing wear
- Worn engine or transmission mounts
- Engine running problems
With the transmission out, measure play between the two masses. LuK gives a maximum rock tolerance of 1.6 mm when the DMF uses a bearing and 2.9 mm when it uses a bush. It also notes that play "can be deceptive and should be measured accurately." A bush-type unit can look worn when it is still in spec.
LuK also lists what kills DMFs early. That includes software upgrades for more power, lugging the car in too high a gear at low rpm, towing or overloading, and engine faults like misfires or rough idle. A tuned Coyote that is driven hard falls into that first category.
Which One Should You Run?
Stock or lightly modified 2018+ GT, daily driven
Stay with a dual mass flywheel and a factory-type twin-disc clutch. You keep the refinement Ford engineered in, and you avoid the added rattle. If the DMF measures within LuK's play limits and the clutch surface is clean, it can stay in service.
Tuned, supercharged, or track-driven GT
This is where single mass conversions make sense. The factory DMF is designed to absorb a certain level of vibration, and LuK specifically flags power-increasing software as a cause of repeat failures. On a 2018+ car, the cleanest route is a complete kit that includes its own single mass flywheel matched to the clutch, such as the McLeod RXT twin disc clutch kit for the 2018 Mustang with 164-tooth 8-bolt aluminum flywheel (6333825M). McLeod rates the RXT Street twin for up to 1,000 hp and says it stays streetable.
2015-2017 GT or earlier 8-bolt car
You are already on a single mass flywheel, so the choice is weight. A lighter flywheel sharpens throttle response. A heavier steel unit launches more smoothly.
- Exedy EF502A lightweight flywheel (1996-2016 Mustang V8 4.6-5.0L, 8-bolt): chromoly steel with integrated ring gear teeth, SFI approved, and Exedy says it is tested to 15,000-18,000 rpm.
- McLeod 463458 lightened steel flywheel (1996-2015 4.6/5.4L Mustang, 11 in., 8-bolt, 164T): CNC-machined billet steel with a 1045 hardened ring gear, built for smooth street launches.
- ACT XACT Streetlite flywheel 600670 (2011 Mustang): a street-weight single mass option.
Always confirm crank bolt pattern (6-bolt vs 8-bolt), ring gear tooth count, and balance against the clutch you are running before ordering. You can browse all options in our flexplates and flywheels collection.
Replace While You Are In There
- Clutch disc(s) and pressure plate. LuK warns that a worn DMF can damage a newly installed clutch, so do both together. See our clutch kits.
- Flywheel bolts. Use new bolts rated for the application.
- Pilot bearing and release bearing. They are cheap compared with pulling the transmission twice.
- Transmission and engine mounts. LuK lists worn mounts as a cause of DMF-style noise and early wear.
- Rear main seal. Check for oil on the bellhousing face while it is exposed.
Cost and Effort
A flywheel swap is a transmission-out job, the same labor as a clutch replacement. That is why it almost always gets done alongside one. On an S550 Mustang, expect a full day for a driveway mechanic with a transmission jack and lift, or a standard clutch-job labor charge at a shop. Adding the flywheel costs little extra labor once the transmission is out. What changes the total is parts: a complete single mass conversion kit, a replacement DMF with a matching twin-disc clutch, or just a lightweight flywheel on an older 8-bolt car. For a full breakdown of clutch choices, read our Mustang GT clutch upgrade guide: Stage 1 vs Stage 2 vs Stage 3.
Frequently Asked Questions
Does the Mustang GT have a dual mass flywheel?
Manual 2018 and newer Mustang GTs do. Ford added a new dual mass flywheel and a twin-disc clutch to the six-speed with the 2018 refresh. Earlier manual GTs, including 2015-2017, use a conventional single mass flywheel with a single-disc clutch.
Can a dual mass flywheel be resurfaced?
No. Worn or damaged dual mass flywheels are replaced, not repaired. Before replacing one, measure the play between the two masses. LuK's limit is 1.6 mm for bearing-type units and 2.9 mm for bush-type units.
Will a single mass flywheel make my Mustang louder?
Usually, yes. Without the arc-spring damper, expect more gear rattle at idle and more vibration at low rpm. In exchange you get quicker revs and less rev hang between shifts.