mx5cartalk.com

About to do a gearbox service and was wondering what the best oil is for my purposes – NB8A 5spd. Car gets dríven on the weekends. Not a track car (but the plan is that it will eventually see WP). Stock engine etc. What im after is butter smooth changes. It’s a bit notchy at the moment. My mates skyline has some redline in it and it feels like the gearbox is floating on air (not entirely a good thing, but i would like a compromise between the two).

Gearbox, according to redline site, I should be using MTL lightshock proof. But what about MT90? Is that more appropriate? All of these oils are offered for sale at Mania so im not sure which one to use. Whats the difference and which will give me smoother shifts?

Diff oil – is diff oil the same as gearbox oil? Ie, could I use MT90 in both gearbox and diff? Or is there oil that is strictly for diff use only? Whats better, mt90 or shocklight proof?

Finally, redline is sold by the quart (946ml) and the NB gearbox is 2L + 90ml in the shift turret. Does this mean I need to buy 3x1quart bottles of redline gear oil? Or can I skimp on the 180 or ml of oil in the gear box?....Also the diff is 1L, where as redline is sold in 946ml bottles…again, can I skimp 50ml from the diff?

NB8A uses the same oil for the gearbox and diff (assuming open diff, if it's an LSD it will be different)

From what you're saying, you need about 390ml of fluid all up.

Personally I wouldn't intentionally underfill either gearbox or diff, it's just safer to do it right rather than have the diff/box sh*t itself because it's had excess friction.

I'd personally get the extra bottle, it means you're covered if you need that tiny bit extra (you spill a bit, it takes slightly more than 2L, etc)


Also make sure to buy a pump thing to get the oils into the box and diff. The pump makes it a really easy job rather than having to weave long hoses through the engine bay etc.

Is there any reason why NA8 would be different to NB8A in this regard?

I emailed Red Line directly and asked about oil suitability for the diff and they said:

Thank you for contacting Red Line Oil, in your Miata differential the 75W90 would be recommended.
The LightWeight ShockProof would be recommended in Spec. Miata racing differentials for example, though better suited for racing rather than all around use, for your spirited drives the 75W90 would be a better choice.

He's referring to Red Line Gear Oil 75W-90.

Also search Sydney Gumtree for Red Line oil, it's $26 per bottle at a place in Eastwood, I picked it up from him after work one evening, too easy.

marty085 wrote:Is there any reason why NA8 would be different to NB8A in this regard?

I can't see why not, same diff, same gearbox.

Read the manual, that's what I did.
I think it just said that both use API GL4 or something.

GL5 for the diff

Thanks guys for info.

Forgive my noobness

From the redline website

Rear Diff 75W90 @ 1 Litres = 2 US Quarts
Manual Gearbox MTL (* Light Shockproof) @ 2 Litres = 3 US Quarts

What grade is the MTL Light Shockproof? is it 70w80?

and for the diff i get MT90 75w90?

Nah, not MT-90 in the diff, because MT-90 is GL4 and is for gearboxes.

This for the diff: http://www.redlineoil.com/product.aspx?pid=133&pcid=4
GL5 Gear oil for diff.

Personally, I put MT-90 in the gearbox. But others put MTL in gearbox as well and in fact Flyin Miata says this about MT-90 in the gearbox: http://www.flyinmiata.com/index.php?dep ... r=10-26020 so maybe i'll try MTL next time.

Dumb question, does the car have to be level (on 4 stands) when filling up the diff and box?

I'd say yes or you won't be able to fill it with the required amount before it starts leaking out the fill hole. Then when its level it wont have enough oil.

Bursons sell Redline oil.

Had some time to change the turret oil last night. With MTL.
Lower and upper boots both torn, probably explains why so much heat emanates from the area. Will probably get them replaced soon.
Was also probably why the shifter oil was black and gunky.
Havent dríven the car yet, but there was a noticeable difference in the smoothness in the shifter.

Does anyone have the NB8A diff drain and fill plug sizes? Got the gearbox drain/fill off with a crescent wrench but the diff wouldn’t budge. Stopped before rounding the bolt off. I’ve read 23 and 24mm? Which is which?

Nevermind, 23 and 24mm.

I would use a 6 sided socket if possible

marty085 wrote:This for the diff: http://www.redlineoil.com/product.aspx?pid=133&pcid=4
GL5 Gear oil for diff.

But a Torsen isn't a clutch pack LSD.

Contains additional friction modifiers for suitability with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required