Transmission Noise - 2016 Mazda MX-5 Miata Convertible Long-Term Road Test

Comments

• meng_mao Member Posts: 24

  September 2016

  Why does it make a noise? The synchronizers are not moving if the trans is in gear, are they?

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• desmolicious Member Posts: 671

  September 2016

  meng_mao said:

  Why does it make a noise? The synchronizers are not moving if the trans is in gear, are they?

  Yeah pliz esplain. The synchronizers are only in use during a gear shift.

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• desmolicious Member Posts: 671

  September 2016

  p.s.that gearshift knob fits perfectly in any previous gen Miata. Got one for my 2013 and it feels (and looks) much nicer than the then original knob.

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• slyons89 Member Posts: 11

  September 2016

  It is my understanding that some of the noises from a lighter flywheel is more vibration getting to the gearbox input shaft. I haven't heard that it specifically affects the synchros, but there is a surprising amount of space in any transmission for 'gear lash', basically margins between the gears. The flywheel is what converts the thumping 1-2-3-4 power of the cylinders into smoother, cyclical power to send to the wheels. A lighter weight flywheel has less damping mass, so it sends more vibration to the transmission input shaft which can then affect the lash of the rest of the transmission. Basically, more of the vibrations from each cylinder firing is vibrating through the transmission and in some RPM ranges, and this is audible to the driver in certain conditions / rev ranges. The input shaft on modern engines is very strong and gearboxes are typically designed to handle a relatively large amount of gear lash from a variety of different flywheel weights, so the lighter weight flywheel shouldn't lead to reliability problems. But it can make some more noise than some folks are used to. Heavier flywheels do a better job of damping the vibration of each cylinder firing and conserve more energy, at the cost of requiring more force to accelerate, and thus feel less 'sporty' when running through the gears.

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• AlexMiata Member Posts: 1

  July 2020

  Also, the explanation sounds good but doesn't explain why it is almost exclusively present only on decel?? This issue has been constant starting with the original 1989 model, but not consistent in that it does not affect every car. And the most common onset is after a clutch change: not pattern emerges that links either a light or stock flywheel, or a brand of clutch kit. It happens (or doesn't) with all combinations. Realigning PPF sometimes fixes, sometimes improves, mostly makes not difference. It is a huge mystery, not yet resolved, not yet logically and convincingly explained by anyone, and there is no conclusive documented and evidence-based fix. Very frustrating if you want to fix it. On mine (NA6), i have had chassis ears on the car and it is most prevalent in the output housing right at the final bushing where the tailshaft yoke rides. No evidence of movement/play in the shaft or yoke or u joint.

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