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Mazda gearboxes....... (some b'stard told me it was impossible so I had to do it!)

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Have now finished the adapter ring. Quite happy with the way it turned out. There was a certain amount of fettling required for the final fit but once that was done it dropped into place nicely - and,

Hello Nick                  How about a stretched limo look? The Satnav had locked onto this? but the view was worth it and me and the Memsahib had a nice picnic and a nice ice-cream on the

Run out of excuses to put it in properly..... quick photo line-up first though Our victim is the one in the middle.... It then got wrestled into place (I'm getting better at i

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Unmolested box in the background.
Easy conversion moves the remote forward the distance between the bolt holes - 104mm. (yellow)
I think you could just about get 175mm and retain the original selector mech (orange)
To match Triumph you need 240 mm (red).  It's less easy......

Meanwhile, at the other end I've been making more swarf,

And now have a ring I can bolt the BH to...

The middle is still in the ring as I have more turntable machining ops to do yet.


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Have now finished the adapter ring. Quite happy with the way it turned out. There was a certain amount of fettling required for the final fit but once that was done it dropped into place nicely - and, pleasingly my centering ring dropped into place without any further messing about.....

I made a lot of swarf...... ring finally separated 


The players......70673EE5-45F6-4780-ACB8-3337084F9112.jpeg

ring in place


and centered 


It’s away to be welded now..... Time to revisit the selector mech.....:pinch:

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I’ve got a rotary table. Not a great one but it works. Useful bit of kit though I’m not sure it’s supposed to be used like this.

This project represents the outer limit of what fits on the machine....... usual story of me trying to run before I’ve learned to walk properly.....

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  • 2 weeks later...

And welded..... he did a great job :smile:


Beginning to have a plan for the concentric clutch too, though I’ll be checking this little lot all fits together and onto the engine before investing.

The shift mods are coming together too, though some way to go.

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So the welded object went  back on the mill to be faced flat and to length.  Some fettling was also need to remove excess weld from a short arc at the bottom before the bell would fit.

After checking that the bell did pull down flat and snug, the front casing was re-united with the rest of the gearbox


And the bell fitted



Then, in order to try it on the engine to check fit and concentricity I needed to make a sleeve to match the input shaft Spigot OD to flywheel hole ID.  These turned out to be rather close in size and odd sizes so the quick and dirty route was to split a short length of 15mm copper pipe.  Flywheel pushed on to prove the concept.....


Then the flywheel was bolted on the spare engine and the gearbox fitted straight on........


.....Phew.  It works.


I will get the flywheel machined to take a ball race as used by Mazda though it will probably have a smaller OD than the actual Mazda one because a) I'd like that to be the same as the Vitesse one (Toyota bearing is a bit smaller) and b) the Mazda one would need a bigger hole than I'm comfortable with.

Happy with this bit.  Now we have the concentric clutch (not too hard) and gear selector mech (fairly tricky) to deal with.  Then things like speedo drive, mounting and whether there is actually any chance of it fitting in the car without major hackery.....


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Clare Rule of Crapengineering Uk makes a concentric clutch adapter for KL V6 to mx5 gearbox conversions. I have it from her that it will work with the standard mx5 set up too. 


Should take you to the files section. I've attached file to here too but I'm not sure itll open. 

Easy enough to make by the looks of it. 








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Thanks all, and especially Arlo for posting those pics. I was aware of the Crap Engineering stuff, but had only seen the single sanitised pic that appears on her website as I don’t do Facebook. So the ones you posted offer much more detail.  I can make that. Would be interesting to know if the exact donor for the concentric slave is named anywhere other than the vague “Corsa” given in the website.  Though I do have to keep in mind that I’m not using a Mazda bellhousing or clutch cover......

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This is the one I'd say. 

The difficult bit for the above cylinder is that it requires a machined channel for the O ring seal that sits under it. I was looking at a toyota  2014/16   CSC013  one for my mx5 engine swap. I dont know the specs however as I haven't pulled one out at the wreckers yet to check. There will be plenty of others that will likely work



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  • 4 weeks later...

I haven't been entirely idle on this.  I've been at the mill again, lightening surprisingly hefty chunks of steel in a very specific way.....

Trying to recreate this "proof of concept" that Chris knocked up from objects found in the scrap pile, which actually worked, in a more robust manner.

selector concept.jpg

The harder part is the knuckle that goes on the selector rod.  This has a socket for the ball on the base of the gearlever which rotates it in an arc around the selector rod to select the gate and forward/back to select gears.  In front of the socket is a set of ramps which interact with a sprung ball plunger to define the gates.

This is a chunk of steel that started at approx 40 x 100 x 60 having the first of the angled ramps put in

selector block 1.jpg

A second, opposing ramp is then cut on the other side.  This one has a step in it as we need to divide it in two to separate out reverse
Selector block 2.jpg

Basically, the bottom of the V defines the 3/4 gate with the ball plunger centering it. To move the lever either way towards the other gates you are compressing the plunger

Forming the rest of the shape
Selector block 3.jpg

Doing things in the right order and not cutting stuff off too early to leave myself with nothing to hold required a certain amount planning......

The still somewhat rough finished object tried on for size....
Selector block 4.jpg
In this pic you can also see the support bearing block on the left.  There is an oilite bush in there and there will be oil seals.  I may yet use a linear bearing if I can find one the right size

Selector block 5.jpg

Still a way to go but I reckon I might build the enclosure/gear lever housing before I invest any more time to make sure it does the job.  Hope so - there are quite a few hours in this.


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  • 1 month later...

So, I am still working on this. The MX rear housing lost a bit of weight on Sunday when I chopped most of the mount for the backbone frame off it. That was a bit of a game. May be some more to go.....

........although, I removed the tunnel cover today (still a horrible job!) and discussed the matter with my tape measure. The tape measure had a good laugh......

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Wrestled the gearbox out this afternoon.  What cow of a job.  Never taken one out of a compete GT6 before.  In deference to my pale coloured interior I took seats and carpets out, which was just as well as it took me a a fair bit of pushing and shoving (and some cussing) to learn the sequence of moves that get it past the heater nozzles - not alot of spare room there - Vitesse is very much easier.

Anyhow..... that allowed this to happen:

Triumph 3 rail/D-type vs. MX5 NA (with bits missing)


Then....... there's no way the MX box is going in the car without the engine coming out or a big chunk of tunnel coming out (and I'm not ready to take that plunge yet).  However, the rear casing comes off pretty easily and the tape measure can accurately tell me where it needs to go.....

.... which is here

.... and it slots right into place, albeit with very little room to spare.




Looks might it might just go.  Low compliance mount needed though!

Also, speedo cable access looks to be between improbable and impossible and tending to the latter.....

I'm feeling more positive about it than I was yesterday

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This gives an idea of the scale of the cut needed to the tunnel..... 


Note the white line on the sound deadening with the MX5 arrow pointing at it.....

If I were to do this (still on the fence pending a successful outcome to the shifter mods), I'd carefully cut the whole chunk out as one and weld an overlap strip to it so it can be put back with bolts.

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That's a big chunk to lob off, but bolted back on, it would be hard to notice. Didn't appreciate how long the gearbox is compared to a Triumph. Short prop needed. My daily driver for the past eight years has been a mk1 eunos.

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That is a very big chunk to cut out!

Do you need to take it off? If the front end of the propshaft is a sliding joint then you don't need access for bolting that up.

Realise it means that without doing so getting the gearbox out is also an engine out but with the handbrake in the way anyway a gearbox removal will be a bit of a bu@@er regardless.

And getting the gearbox out of the back of the six is a lot more work that with the four. Especially with the GT6 heater box and the extra cold air outlets - as you have now found out.

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It's not that big a chunk - and only tin.  Plus the handbrake comes off in about 30 seconds

Frankly I'm not even remotely interested in an arrangement that requires engine removal to access the gearbox/clutch.  Especially as this will have a concentric slave.  Remove bonnet, then best part of 250 kgs of engine and box..... and you'd still have to remove half the interior :pinch:

Yep, I have done gearbox removal on every other Triumph (bar TRs) and none as awkward as this, though the 1500 Spit box must be a fairly close second given that it weighs as much as a small planet.  Was no fun hauling it in and out of my Herald as I recall.

Still contemplating OD repair..... but it would still be a noisy, leaky fragile thing.

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  • Nick Jones changed the title to Mazda gearboxes....... (some b'stard told me it was impossible so I had to do it!)

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