ND grinding/grating sound on decelleration

[Mixie]

Hi there. This is my first time in the MX5 forum. In December 2015 I got my 2.0 litre ND Roadster (ordered without test drive because none available in the country). Since that time Mazda have tried unsuccessfully to identify and fix a grinding/grating sound that occurs at revs specific to each gear and always on deceleration. The noise occurs in a very narrow rev range and I can top it by very lightly touching the accelerator, or simply changing up a gear which I don't want to do going down hill.

Has anyone had the same issue? Mazda replaced the diff and gearbox (under warranty), and still no change. Eventually that said it was just
"the nature of the car". Very annoying nature, and the only thing I don't like about the car.

[bruce]

Hi,
Welcome to the forum.
Sounds like you and Mazda have tried to fix it, even by replacing the gearbox and diff! I don't think we can add much to it as I'm sure all avenues have been followed up.
What you could be hearing are just normal noises made by the gearbox or diff, enhanced by the car being a lightweight convertible. Have you dríven another similar specced car to compare noises?

[KevGoat]

Welcome Mixie ... as Bruce mentioned there's a lot more mechanical noises noticeable when driving an MX-5 compared to "normal" cars. Have you dríven or passengered in any other 5's? You could ask if any other ND owners are nearby and willing to give you a ride along, this might be one way of seeing if you hear something similar in their's too. I know with my roof up in my NB I hear a lot of driveline noises I've never heard in other cars and this use to worry me but use to it now. Not much soundproofing in these.

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[hks_kansei]

As others have said, try and ride in a few other MX5s and see if it's normal.
I havent been in an ND, but I know the NA/NB are more rattly than the equivalent age Mazda 323


Generally a grinding/whining on decel would be something like the gearbox/diff having incorrect lash adjustment, allowing the gears to mesh slightly off and cause noise.

The fact that it's a specific rev range though (I'm assuming by that you mean costing downhill in 4th it makes the noise around say 3000rpm, but stops at revs above or below that?)

If that's the case, it may well just be a harmonics thing, the car at those revs/load causes something to vibrate in just the right way to rattle.

a lot of NAs and NBs have a similar thing where at about 3000rpm the heat shield over the exhaust will often start to vibrate just the right way to make a godawful noise.



if you have access to something like a gopro camera etc you could always just stick it at a few points around the car and see if you can narrow down where the noise is loudest (ie: if it's loudest when the camera is at the back it may be diff, if at the front, maybe something in the engine bay, etc etc)

[93_Clubman]

The following two Mazda Technical Service Bulletins detail known MX5 ND transmission issues & might be worth a look to assess if applicable to your MX5:
https://www.miata.net/garage/tsb/Unusua ... 20Gear.pdf
&
https://www.miata.net/garage/tsb/05_007-16.pdf
Most Mazda Technical Service Bulletins can be found here: https://www.miata.net/garage/tsb/

[greenMachine]

The following two Mazda Technical Service Bulletins detail known MX5 ND transmission issues & might be worth a look to assess if applicable to your MX5:
https://www.miata.net/garage/tsb/Unusua ... 20Gear.pdf
&
https://www.miata.net/garage/tsb/05_007-16.pdf
Most Mazda Technical Service Bulletins can be found here: https://www.miata.net/garage/tsb/

The sad story of the ND 6-speed transmission is by now (fairly) well known. There have been several major gearbox mods made by the factory, and a number of minor mods. If they have replaced the transmission:

a) what changed, did the noise go away and then come back, or not go away at all, or came back in a different form (softer, 'different', etc)?

b) what did they replace the transmission with - another one removed from a different car under warranty, an original 'spare' that had been sitting on Mazda's warehouse shelf since the first cars arrived, or a brand new one fresh from the factory?

If it is the same noise (volume, nature) as caused them to replace major components, they can't really say 'too bad, so sad' and walk away from you.

My first move would be to get the serial number from the gearbox, and see if you can identify the production date, and what mods were supposed to have been done to it. That information should be available from the big board (Miata.net). You should also be able to identify what (if any) mods were supposed to have been done subsequently. That should give you a solid base to go back to Mazda and seek another gearbox replacement if there are mods done to subsequent production runs of the gearbox.

[Mr Morlock]

As a few already said- best to get someone else to drive the car and see if they are aware of any "abnormal" noises. You could also get a drive in one of the later model cars and see if these have the same noise. Replacement of a gearbox might not be the answer i.e. its known that with certain other cars with gearbox issues ( not MX5s) faulty gearboxes are replaced with similarly substandard boxes that exhibit problems further down the track. Alert guys on the forum have also spotted problems with the boxes of a certain time so it does point to some issues which may be be addressed with later changes.

[Mixie]

Thanks everyone for the welcome input. I'll work through it all.

[paueee]

I get the same noise in my 2016 ND 2.0. Sounds like a spinning chain rubbing on metal.

I think it comes from the engine bay though not the transmission. It was more noticeable when I had the sound tube. Ever since I removed the sound tube, that noise still comes and go but not as often as before.


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