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I may be mad...

My na6 has the imfamous rattly grinding noise on deceleration between 2500rpm and 3500rpm. My though was that it possibly could be the throw out bearing, but talking to Juffa on a recent drive it is more likely that it is caused by back lash in the gear box caused when a new clutch goes in.

The na8 diff comes with a heavy duty rubber mount which absorbs the vibrations, the na6 diff does not. People with the noise report that fitting an na8 diff stops the noise.

Not being able to afford an na8 diff and slighly annoyed that I have to constantly drive around this horrible noise I'm thinking that maybe I could make up a rubber mount similar to the one on the na8 diff and mount it between the tail shaft and the diff.

Now, the questions... Firstly has anyone tried this? Would the say 5mm of rubber cause the mechanism between the tail shaft and the diff to not work properly? If it possibly could work I assume it wouldn't be too hard to do. I would probably get a diff shop to take everything apart but looking at it it shouldn't be too hard to get it apart and try it. Has anyone got a picture of the rubber on the na8 diff?

What do people think? I may be crazy, but I would be thrilled if it works!

Cheers,
Ben

Yes, you are mad.

If you have a mechanical noise it is because something mechanically is not right with the drivetrain. Take it to a drivetrain specialist, and get it diagnosed and fixed properly. The NA8 diff has a vibration damper but it's not designed to make up for a gearbox or diff about the implode.

Hmm, actually I think this is a common issue with na6's and from all accounts not indicative of a failure. A number of forum member has reported similar issues after a clutch change. I've also dríven a few other na6's with the same noise. Here is a large thread on miata.net about it http://forum.miata.net/vb/showthread.php?t=56224

Thanks for the reply though.

I also found these thread on here to show its a common(ish) noise.

viewtopic.php?f=18&t=18553&hilit=deceleration+grinding

viewtopic.php?f=29&t=20583&hilit=deceleration+grinding

viewtopic.php?f=29&t=28369&hilit=gearbox+rattle&start=15

Question ... does yours also do it on acceleration ?
sound like its coming from the exhaust ?
a kind of buzzing ?
can you stop it by lightly pressing the clutch ? (not throwout bearing, but actually starting to take up some spring...)

Mine appeared straight after the clutch change too .....

very annoying, but i managed to 'fix' mine ....

I fitted a 12" sub

yea, its still there, but i cant hear it .. in fact after driving for a while, i cant hear anything

But seriously, I'd love to find a "solution" to this noise .....other than a complete gearbox / diff rebuild !

Cheers
J

Mine does it sometimes under acceleration, but rarely, where as the deceleration noise is constant when the car is warmed up. It does go away when I slightly engage and ride the clutch, which makes me think the gearbox backlash theory is creditable.

Also, the fact that it doesn't occur when the car is cold could indicate that thicker gearbox oil could reduce the problem...

As knowone seems to know if its possible or plausible I'll find the time to drop by a gearbox/diff place next week and sound them out.

My diff was making noises like that for around 2 years.
A clutch change & added sticky tyres was enough to break the diff within a very short period of time. I wasn't pushing it when it exploded.

NA6 diffs are not the strongest.
yes i do like to drive my car hard. But never, did I do wheelies & try to chirp the rear wheels when changing gears. My original clutch lasted 192K km. so that should show that I do treat my car with respect.

Your diff is most likely going to go eventually. If you treat it with care, you can make it last longer by treating it extra careful. How long its going to last is really hard to say.

Its quite possible a technician will not pick any problems as a hairline fracture is pretty hard to pick up.

I'm all the way with CT. But calling you mad is prolly a little harsh, but then you did ask for it.

drive your car with joy .....just be ready to replace the diff when it happens. hopefully it will not happen in a really aquard place.
I replaced my diff with a 1.8 torsen. It still is the single most exciting mod I've done. And I couln't afford it either at the time. But it was worth every cent.

Hmm, ok... So there is a good chance it could be the diff, although the noise seems to be coming from no where near that part of the car. Makes sense that it could be the diff though... However, would an open diff actually be doing anything under deceleration to cause a rattle between certain rpms if it was about to fail.

Has anyone had this noise, blown the diff and replace it with a new na6 diff and fixed the noise? I ask this as the diff you put in has the rubber damper.

Is it possible that all people with this noise have a diff which is on the way out? However that doesn't expain why some people on miata.net have had the nosie since the car was basically new and had no issues for 100,000k +

Hmm...