Gearbox out, what else should I do?

[Custardtart]

I'm taking my gearbox out to fit new plastic bushes, tbh I don't really know if they need replacing but I have been having a slightly crunchy 4th to 3rd shift and the classic 3rd to 2nd.
Is there anything else I should be doing whilst I'm in there? Any way to beef up the NC1 'box?

Below is a tutorial on the plastic bushes.
https://www.mx5parts.com.au/blogs/news/ ... box-issues

[Custardtart]

https://forum.miata.net/vb/showthread.php?t=237737

This is an interesting read, looks like there’s a few things that can be done to beef the 6spd NC01 box up

[greenMachine]

That is an interesting read. First I have heard of the NC1 box being the same as the SE/MSM. Also interesting that there are no followup posts, not sure what to make of that but my gut tells me it is not a good sign. Is that all you could find there about the NC gearbox?

I understand that there was an upgraded box for the NC, not sure when this was introduced or what the upgrades were. You might want to do a search on MT.net, there are few people with NCs there, and because of the NA/NB gearbox issues there is bound to be some discussion. The other source would be GWR's forum, they did put a lot of effort into the NC.

[Mr Morlock]

I reckon JBT would be worth contacting- I know he grumbled probably accurately about noise ( clatter) in the gearbox. The link looks pretty straightforward and presumably if parts are to be replaced then have them ready for changeover. Gearbox specialists - are there any and what does it cost to fix " problem"

[hks_kansei]

Gearbox specialists - are there any and what does it cost to fix " problem"

Gearbox specialists still exist, my partner was one before changing careers.


Cost wise, it's not cheap.
A gearbox rebuild is very labour intensive, and to do it properly requires a lot of careful measuring and knowing how much play each part should, or shouldnt, have.

From memory a standard gearbox rebuild for an MG 4 speed was around $3,000 (including removing from the car and refitting when complete, which is apparently a 40min job each way on an MGB), with the price increasing if the box needed larger parts replaced (ie: bent layshafts, missing gear teeth etc)
And with the price increasing more if the box was to be setup for racing (tighter tolerances, stronger components where needed, etc)


So yeah, full rebuilds aren't cheap.

[93_Clubman]

GM, my reading of the following is that the MSM & RX8 share the Aisin as opposed to the MSM & NC1.

This transmission is an all new gearbox, designed in house for this car. It is NOT shared with the RX-8, as the rotary car has an outsourced AISIN box. The Mazdaspeed MX-5 Turbo has this same AISIN box. That box has it's own problems, and that's a whole other thread.
https://forum.miata.net/vb/showthread.php?t=237737

[Custardtart]

GM, my reading of the following is that the MSM & RX8 share the Aisin as opposed to the MSM & NC1.

This transmission is an all new gearbox, designed in house for this car. It is NOT shared with the RX-8, as the rotary car has an outsourced AISIN box. The Mazdaspeed MX-5 Turbo has this same AISIN box. That box has it's own problems, and that's a whole other thread.
https://forum.miata.net/vb/showthread.php?t=237737

Not sure about NB boxes but the NC1 box is not shared with the nb or nd.

[greenMachine]

Yes, I think I misread that part.

I think that rather than putting effort into an NC1 box, I'd get an NC2 or preferably an NC3 box. If that needs the same treatment, so be it, but the internals should be the latest spec.

Remember, it is only money ...

[Custardtart]

Yes, I think I misread that part.

I think that rather than putting effort into an NC1 box, I'd get an NC2 or preferably an NC3 box. If that needs the same treatment, so be it, but the internals should be the latest spec.

Remember, it is only money ...

I agree GreenMachine but they’re like purple unicorns!