1990 Eunos roadster (NA Miata) auto gearbox issues

Hey guys!

Still me and my yellow mx5, this time with a quite unusual issue I would of thought.

When i got this car it was my first project and for whatever reason i decided to strip and refit everything with a clean, which was a mistake now I think back to it.

So part of the interior stripping I removed the automatic gearing mechanism, I still don’t know why, had a look, and put it back together when I decided it was a good time to put everything back together.

But ever since then all the gears were messy, I couldnt get into park, the furthest I could physically go, which showed up as “P” was actually reverse, then “R” was neutral, '‘N’ was then drive, I guess ‘D’ was 2nd gear and “2” was 1st gear, no idea what ‘1’ was but I think it went down enough to there, and anything under ‘P’ was smooth when going through, there was no resistance when going on each gear, it was all over the place!

And of course not having park means I couldnt take the key out and could use it on things like my boot, leading me to have to take out the boot mechanism, so it was a chain reaction of problems.

It’s been a year now and I got used to it, but no way would I pass the MOT with this, atleast I don’t think, I need to get it ready for its first MOT and would love to get this fixed but I was completely clueless as I was disassembling today like I was a year ago.

I tried take the whole shifter out until only the gearing rod was there, tried to push that as far forward as I could hoping that was park, I knew when it wasn’t reverse because mx5s give out a beep when they are in reverse, unless I was in neutral, I’m pretty sure I was in park if I was pushing it forward, but I had no way of telling, and the key still won’t come out or turn back fully to the lock position.

Upon inspecting the shifter I didn’t understand anything, like what the wires were, why I had two random white wires, and was this weird box was with a piston sticking out that I could push back and forth with a handle.

To say the least I have no idea what I’m doing and I apologize that you have to hear this story of a problem I brought into myself but I’m hoping someone works in the dumb division and could fix this unusual problem I saw noone else have

I have attached some pictures of what I was doing incase anything looked wrong (pretty sure everything does)

If there’s anything I missed or badly explained , let me know, I’ll go more in depth and do it as I’m with the car , since I’m writing off the top of my head and just needed to reach out to the master race for ideas

Appreciate the time and I hope you enjoyed reading that, I think I should get top marks on my English essays!

To update ya’ll, I’m at school but my dad received the new automatic shifter mechanism, the gears now are right, probably because he got the linkage in the right place this time, rather than it bring a new mech, but I needed a new one anyways.

But there is still a problem, the key still won’t come out the barrel even in park, could it be something electric? I cant give anymore info until I see the car myself on Friday.








Suggest you ping Mazdamender (forum member), as he knows these autos quite well.

Diagram of the shift mechanism might help:

I’ll do that, and also tinker around with the shifter looking at the diagram, you think something not letting me take my key out is an electrical thing?

@Mazdamender your assistance is required good sir

With our current mechanism falling to pieces I think it sounds good to order a complete mechanism off eBay for £40 which i did not think about

Mazda MX5 Mark 1 mk1 Eunos auto shifter gear lever rubber gaiter Mechanism | eBay)

It might be a simple case of the shift knob being in a different gear to the transmission rod when reinstalling, I assume I’d have to have it in “N” when reinstalling, althought there is an odd number of gears.

I’ll hopefully wait for a reply from mazdamender for anymore info

Sorry i am late to the party , thanks for the heads up saz, OP let me get through work here and i’ll have a good read up on whats been posted so far, and we’ll get you sorted bud
M-m

Appreciate it! Apologies if it’s such an unusual issue😂

I have just done a manual conversion, if you need any parts let me know and ill take them out the bin for you.

Appreciate the offer, would it be quite difficult or time taking? Since it’s just me and my dad in an open shed with nothing but spirit and a few weekends😂

I have been thinking about making myself a little drift car…

To update ya’ll, I’m at school but my dad received the new automatic shifter mechanism, the gears now are right, probably because he got the linkage in the right place this time, rather than it bring a new mech, but I needed a new one anyways.

But there is still a problem, the key still won’t come out the barrel even in park, could it be something electric? I cant give anymore info until I see the car myself on Friday.

The cable is disconnected or not fitted correct at the selector that pushes the pin on the ignition unit to release the key.
The two white wires…they have been added from someones butchering to the black wires under the electrical tape,and are for the over drive button to work.
So she is all sorted in going through selecting and park?
Leave her in over drive for use(light off) keep an eye on the oil for level,smell and colour also if staying an auto I recommend changing the diaphragm .
M-m

Is this the diaphragm? Auto Gearbox Vacuum Diaphragm, MX5 Mk1
Sure there’s a video on replacing it wherever it is.

I could of swore the OD worked before, but I’ll test everything out when I’m back.

Haven’t touched the transmission fluid since I got the car left under a tree a year ago, so probably should change it.

Car smells abit rich, maybe burning alot of fuel, maybe it’s just old, can’t tell the fuel because the fuel gauge doesn’t budge so that’s my next job.

Thanks for all the tips, and I’ll come back to you on Friday!

Thats the baby, it can cause big problems if it fails and can with age, most garages will not see the symptom and the correct cure and will have you over for a new engine and labour

http://www.mazdamenders.net/forum/viewtopic.php?f=124&t=7209

Check that the O/D is back connected other wise you will be using more fuel .

As for the fluid , just check level,colour and smell, it should have minimum smell and be red( power steering fluid Dextron II) if it really smells and brown in colour ,then it will need changing.
She will burn fuel if the O/D is not on, but could be a number of other small issues to investigate.
Have you solved the cable/switch key issue?
And she is selecting gears now yes? and engaging park?
M-m

should I check the diaphragm if it’s simple or just buy the new bit assuming it needs changing, then find out where it is.

So what exactly is overdrive in human words since I don’t get Google, just to save fuel?

I’ll have a look at the oil, and also fuel can be anything as you say, I mean I’ll make sure to stay on O/D for now. It idles pretty rough I feel, sometimes 600 rpm when I first start it, or when the RPM is dropping back down after a rev, it goes below 1 like if trying to catch a bowling ball.

At one point it was cold and after abit of running on idle it just stuttered and stopped, but I’m quite sure that was just not enough fuel, I never know until I get that guage sorted.

My dad got the new mech in (since I’m at boarding school all week) and the switching gears was all right and back to normal, I’ll have a look at the OD and the key when I get back later today.

Thanks for helping so far, really appreciated!,

Was able to have a look at the car.

Sure enough the key is still in there, and only goes down to ACC(II), but not Lock(0), like if something was blocking it.

Decided to open our new gear mech to see if he missed any wires, but while I was doing that, I played around with the rod sticking out of the black box, and it was down, but when I pushed it up I see it locks the gear in park, (was trying to see if that gets the key out) but now each time I push the rod back down , it magically and slowly cones back up, locking me in park.

Atleast park works now, but two new issues, the key won’t come out (won’t even rotate to 0) and now I get automatically stuck in park , even if I use a screwdriver each time to push the rod down through a designated hole, I still don’t think that’s how my miata should operate haha

Video being loaded to you tube as we speak, will link when loaded.
M-m

M-m

Thanks again for the video.

Slight different and contradicting question,
Is the bell housing from a MK2 the same as a MK1, if I were to manual swap my MK1, could I get the full gearbox from a MK2 with no issues

5-speed or 6 speed will work, but with an auto engine, yoju probably want a 5-speed. Same gearbox as a Mk1, but the shifter is slightly different.

Fair enough, as long as I know it would be a straight fit.

Just had same thing done.
Mine is an 1840cc '94 which I’ve owned as an automatic for over 16 years.
Put a 5 speed in. 6 speeders can be a mixed lucky bag. I own a 2002 Sport as well witrh the six speeder and it’s OK but the 5 speeder as far better in my view.
Don’t know what your O/D used top gave you at 70mph…probably around 3100rpm or so.
Just be aware the 5 speeder will be a bit more frantic at around 3600 rpm at 70mph.
But…it’ll lug around town in 4th & 5th all day long.
My 1840 pulls clean from 30mph in 5th. But then, it’s a bit of a freaky engine… oddly energetic in apparent standard form and no one knows why. I blew the OEM on track…so it was a full mill replacement from sadly a now defunct but back then trusted source.
So anyway…bla de bla…5 speeder way to go. Don’t forget the DVLA & Insurance changes.