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Hi folks,

98 NB8A with close to 300k kms, stock, and a decent whine particularly when cold but still present once warm.
The noise is there when the car is moving or stationary, in gear or neutral, but goes away when the clutch is depressed.
Leads me to believe input shaft bearing would be the most likely culprit? Any other ideas?
Geaxbox oil level is fine but will be changed over christmas.

Sounds more like the clutch. Since noise is there when stationary.

Welcome back Jeo - sounds like clutch thrust bearing &/or clutch pilot bearing aka spigot bearing. Had to do mine a couple of years ago, so bought the kit, & replaced the bearings as well as clutch pressure plate, clutch plate & rear main seal.

I'm with you Jeo, being the input shaft bearing, but I would have thought it would get noisier as the temp comes up.
If the noise goes away when the clutch is depressed then I'd say the throw-out bearing is ok, because that's when it's 'in play'.

Yes, input shaft bearing. You're only getting the whine when the input shaft is turning. 10-120% chance that changing the gear oil might fix it, especially if the old oil is old or low quality.

Penrite Pro Gear full synthetic GL-5 75W-90 FTW in an older gearbox.

Ooops 10-20% not 10-120%.

Thanks folks. Full set of fluids acquired today with boxing day sales, including gearbox.

I'm not all that hopeful it'll solve my problem but feels like the easiest and cheapest thing to try first. Will report back.

In the 5 minute drive around the block I'd say the fresh gear oil has improved the whine, but certainly not fixed it.


So I guess the next question here is what happens if I do nothing? It eventually goes pop and grenades the whole box?
How hard would it be to replace the bearing?

Do the 6-speed swap.

With the NB8A diff, you get better acceleration (especially noticeable in 3rd-4th), and they are generally stronger. Pulls a few more revs in top at freeway speeds, but that is pretty meh, it is a sportscar after all!

You then install one of MR's tall short shifters, and get back the decent change that you lost with the new box.

Looks like I'm up for another 6 speed, this fell out of the drain plug today...

That's not just a wave washer from the shifter turret?

beavis wrote:That's not just a wave washer from the shifter turret?

Will have a look.

Magpie wrote:

beavis wrote:That's not just a wave washer from the shifter turret?

Now how do I replace it?

Buy this?

https://www.mx5performance.com.au/colle ... mazda-mx-5

Well done BB, sharp eyes, AND a solution!!