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I know this has been flogged before but I can't find the information posted on gearbox oil suitable for a "96 NA8. Can anyone point me in the right direction please?

Castrol VMX-M

The 5 speed box is the same from NA through to NB.


The same oil is used in the diff as well (for the standard open diff, LSD often require different oil)

More broadly for GB oil the factory NA8 Mazda MX-5 Owner's Manual indicates: GL4 or GL5 of 75W-90 (for the full temperature range) or 80W-90 (for 8 degrees Celsius & above).

I've seen Redline MT-90 suggested a lot. I have used it in the turret of my NA6 but not yet in the box.

mx5mania sell it on their eBay store I believe.

93_Clubman wrote:More broadly for GB oil the factory NA8 Mazda MX-5 Owner's Manual indicates: GL4 or GL5 of 75W-90 (for the full temperature range) or 80W-90 (for 8 degrees Celsius & above).

That's the stuff.

I couldn't remember the specs off the top of my head, but I knew the VMX met them. (did the box oil on mine over the weekend using the castrol I bought ages ago and never got around to putting in)



to the OP,

when you do the gearbox oil make sure to fill it correctly, there are some how to out there that are suggesting removing half the interior and filling from the shifter etc.

The correct way is to fill from the fill plug on the box (14mm square ended plug on the passenger side of the gearbox)
Remove that, then remove the drain plug, once drained put the drain plug back and tighten.
Then simply fill from the fill hole until the oil starts to dribble back out again.

The diff is done the same way.

Be sure you take the fill plug out first, cos some people have had issues with not being able to get fill plug out and only finding out after they had removed the drain plug and emptied the gearbox of fluid..

To fill the gearbox you go at it from underneath however there is no way for the 5-speed to transfer oil back up to the shifter turret so it is good practice to clean out and replace the turret oil at the same time.

Over time it does run dry, either from draining down the selector rod into the main GB housing or leaking out of the selector rod tube seals, side plate gasket, torn or missing lower shift boot or the detent bolt washer.

From memory it is 70-90ml of oil to service the turret. I used a syringe with a piece of washer jet hose attached to get right down in there and get the slime out before topping mine up. Going from little/no oil to a freshly filled turret did make cold shifting on my old box a lot easier.

This is the turret off the box. I couldn't find a good close photo of it mounted to the box that shows how it is separate from the main housing.

True, but since the selector is under a lot less load than the main box fresh fluid isn't as important there.

If it's empty it's usually a sign the seals are stuffed and it's drained down into the main box, in which case constant topping up can overfill the box (100ml wont matter, just dont check it every few weeks and top it up constantly)

TRANS 75w90 GL4

DIFF 75w90 GL5

I changed from whatever old stuff was in my NA6 from the previous owner that was long overdue for a change to Redline MT-90. Night and day difference. I can't compare to any other fresh oil but the box shifts beautifully now..