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

Nick Jones

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Not sure this is going anywhere... but we have a growing collection of Mazda gearboxes.  An RX8 5 speed, and MX5 NB 5 speed and most recently an MX5 NA.

Decent gearboxes.  Tough enough, nice change, reasonable ratios.  Cheap.  Really.  These three in total have cost (much) less that the parts alone used for the GT6 gearbox rebuild.  And while that works well enough, it is not as quiet as I would like (spoiled by Toyota!), and has a dodgy overdrive - reminding me why I went to the fairly significant effort of putting the W58 in the Vitesse.

Anyhow...... there is a reason (well, several in fact) why people aren't putting MX5 (or RX8) gearboxes in small chassis Triumphs.  It's not easy.

- Though they look quite small, in pictures and even in the metal, they are not.  Actually 140mm longer than the W58. 

The red arrow shows where the gearstick need to be to match the Triumph box.  There's great chunk of aluminium on the side of the tailshaft housing which needs chopping off.

- The bellhousing is integral to the front half of the casing.  At first glance,


even second glance,


it looks like you might be able to do something on a 6 cylinder with a new engine backplate and perhaps the Mazda starter.  The flywheel being (just) too big to fit in the bellhousing.........


is very unhelpful though.

- Chopping the bell housing section off is possible but you won't get a convenient flat surface to drill and tap.......


There is an adapter plate available from Retro-Ford to join them to a Zetec SE...... which might solve Chris's problem

Or this from Vitesse


Bit over my budget though!



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A martey with an SP250 is faffing about with an MX5 conversion.

His plan is to get a new flywheel made (£££) so he can use the MX5 clutch and starter, along with an adapter plate. I guess he should get a batch of 10 made up, bound to be takes if he can get the flywheel and plate ciosts down to about £300. Makes the boxes look expensive, but compared to the NZ w58 conversion it is a steal....

Cureently the R*8 boxes are flavour of th emonth, but I expect the supply will soon run out. Then the MX5 conversions will really get under way.

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13 hours ago, Nick Jones said:

That's not that much more than a T9 conversion. Perhaps not within everyone's budget but there will be many who would not hesitate at the cost.

 I have always had to do my projects on very tight budgets and I get great satisfaction achieving my improvements at a fraction of the cost of off the shelf solutions. Saving the money allows me to do more improvements or to shell out for the items not available for a "bargain" at the right time, they turn up a few days after you have made the "painful" purchase. 

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I looked really hard at this once- before switching entirely to mazda engine and box.

The RX7s use similar boxes- differences are mostly in the casings.

The rx7 series 1 box. The bellhousing on this fits the mx5. It's a little wider and a bit shallower meaning it's not quite as long as the mx5. There are fewer bolts mount it to a back plate so, simpler. A couple of good points are that the clutch fork operates from the top of the bellhousing- so wont hit the chassis rail like it will on the mx5 bellhousing. Also the starter is mounted inboard on the other side (where the slave is on a herald bellhousing) although I cant verify whether that will hit the chassis rail- I think it's close, but will sit above.

Moving the gearlever up couldn't be easier on the mx5 box- it's about 30min job. Itll get close to where your arrow is- probably within 2 inches without getting really inventive. The lump on the side is easy enough to grind off. 

However, the box is just a bit longer than a type 9, so on a six, where you can't move the engine forward, you are getting into funky prop angles and would need to move the handbrake/tunnel back a bit. 

Also the speedo drive- I ended up cobbling a right angle drive to it and it *just misses the chassis rail without inner cable chewing bends. But- later mx5 NB series use electronic pick up that can be easily retrofitted- whether converting the gauge is easier?

Pictured rx7 S1 box

Screenshot_20200711-001528_Trade Me.jpg

Screenshot_20200711-001521_Trade Me.jpg

Screenshot_20200711-002854_Trade Me.jpg

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Thanks for the RX7 pics. Interesting variations there. Pity that the older Stuff is really quite rare in the UK now.

Background to this exercise is twofold.  I have a long-standing dislike of the original Triumph gearboxes - simply not strong enough for the duty, especially on the 6 cylinder engined cars. I do appreciate their nice ratios (6cyl) and decent shift quality, which is why I went to some effort and expense to rebuild the GT6 unit. Thing is, in spite of stripping 3 complete boxes, I still had to buy major components and get machining done to recover others.  This has won me a gearbox that works reasonably well but is noisier than I would like and has an overdrive that doesn’t work as it should. Meanwhile, I can buy a complete working MX5 gearbox for less than one (slightly dodgy copy part) Triumph synchro ring......

On the other hand, Chris is still considering an engine swap with the Ford Zetec SE 1.6 plus MX5 NA box being the front-runner Until very recently.

Then he discovered the world of Suzuki G an M series engines and the fact that they can be fitted to Suzuki 410/ 413/ Samurai/ Vitara/X90 RWD gearboxes........ These gearboxes are very small and light with (in some cases) decent ratios and actually pretty tough.  So now that avenue is being explored.  A friend locally has a bit of a Suzuki “problem” and has let us have a box on approval......

MX5 box sat on the spare chassis with the front face in the 6cyl position......


look how far back it goes.....


The Triumph box gear-lever is roughly in line with the middle outrigger.

The Suzuki box though.....


Obviously the lever needs a bit of reduction surgery.....but 

Now this is no good for a 6 cylinder Triumph lump, but with 100 bhp stock available from a variety of compact, lightweight Suzuki power plants, perfect for a Spitfire. Engine and box seem to come in at a little more than 100kg!

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1 minute ago, mpbarrett said:

Interesting, what do you do about the flywheel? Can you modify a Suzuki flywheel or adapt a Spitfire one?


We’re not considering trying to fit the Suzuki box to a Triumph engine. That would be hard. Very hard.

It’s a means of getting a RWD box on a light and efficient modern engine.

Possible fly in the ointment is that the gearbox mates to the G series engines. The 1.3s directly and the 1.6s with some simple mods. Performance versions of these are relatively few. The Swift 1300 GTi from the late 90s would be perfect. If we can find one.  The later M series are much more plentiful and several variations has numbers as good as or better. However, it’s not entirely clear how well these mate to the gearbox. Research continues.......

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More messing about today.  Having collected a few specimens to help my thought processes (thanks Mark)  I now have a Vitesse bellhousing plus the bellhousing from a 2000/2500 BW35 auto and matching saloon engine backplate.

I've also worked out how to take the front casing off the MX5 gearbox (easy).

Top - MX5 NA box with front housing separated.  Upper middle - Vitesse/GT6 bell, lower middle, T2000 auto bell. 


The conclusion is that in order to stand any chance of using this box, the front casing is going to need radical surgery with roughly the front 175mm removed.  The Vitesse/GT6 looks like a non-starter but I think it would be fairly straightforward to make an adapter ring to weld to the cut-down casing and bolt the T2000 bell to that.  This approach would require a concentric clutch slave.

MX5 bearing cover just about fits into the inner diameter......

So possible, but not particularly easy.  Not the only challenge to overcome either.

Then I offered up my very rare (in UK) W58/22R bellhousing,  just for because I'd found it earlier looking something else.....

And that looks like you could make a new backplate to get the job done....... Hmm.  Thing is though, you can buy an MX5 box for < £50 and W58s are > £ 800 and rising - if you can find one that hasn't been smashed by the drift brigade.  I have a spare W58 but......  May invest a couple of hours in making an MDF backplate though.


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So this could be a red herring....... but, I'm trying to discover whether I might be able to obtain a gearbox front housing for the MX5 gearbox that will bolt right up to a Triumph back-plate.  And while that is a possibility I'm reluctant to start hacking a perfectly good casting about.

Any how,  I mentioned above that I'd come across my "special" bell-housing for a W58 gearbox.  This didn't feature in the original Vitesse conversion as I didn't have it then.  I knew they existed and reckoned there was potential, but I couldn't find one.  Possibly never fitted to a UK market vehicle.

The one here came from the USA.  IIRC it came from a Mk1 Hilux pickup with the 22R petrol engine.  Very reasonably priced and the guy didn't even blink when I asked if he would ship to the UK.  It's been sat here for years, still with US mud on it.  Point about this BH is that the starter housing is on the right, quite close to the Triumph location and I wondered if it could be fitted as it is using a bespoke back-plate - which is fairly easy to make.

With all the bits to experiment with close at hand, it seemed rude not to.

So I grabbed a piece of 9mm MDF sheet and used a stray Triumph backplate to template the engine bolt positions and the round hole in it which is handily concentric with the crank to find the crank centre.  We also marked the flat on the bottom of the backplate as a clocking aid.  Then used a hole saw to make a round block, drilled a 12mm hole in the very centre of that to go snugly on the gearbox input shaft, centred this over the crank centre and screwed it down.

This left a flat board lying on the floor with a  raised section in the middle with a hole for the input shaft spigot, so we updended the gearbox and popped it on.  Turned out that the flat marked from the Triumph plate lined up very handily with the flat on the Toyota BH, making the clocking pretty obvious.  Next step was to use the BH as a template to drill through the board to get the outer ring of holes.  Easy.  Then draw round the outside, pull the box off and cut round with a jigsaw.

At this point there was no good reason not to bolt it to an engine......




Chris managed to find the original spigot bush I made for the Vitesse (now replaced with a proper bearing) and I found my spare clutch plate... 

Not completely issue free


Two pairs of key holes are really rather close.  This can be got around.  Can probably turn the gearbox a few degrees clockwise relative to the engine, which will also put the starter nearer the Triumph position but threatens to put the clutch slave into the chassis rail..... the art of compromise.....

Then the box fitted up

Looks proper enough

Starter position

We marked the start centres for both Triumph and Toyota positions and they are within 1mm so, as Toyota starters have previously formed the basis of a starter that fits a Triumph (have a CC converted one on the Vitesse) I'm confident there with be a standard item that with bolt right up and work.  Just don't know standard to what at this point.

Had previously offer it up without the clutch fitted to see how good the face to face dimension was....

NOt bad.  Could probably do with the BH being shorted by 3 - 4 mm.  I can do this easily enough but would wait until the steel plate were done before committing.  Looks like the standard Toyota clutch release system will also work, though I am a bit wary of this as this is almost exactly what I have on the Vitesse and it has some unexplained oddities!

In summary - I reckon this is a viable, even straight-forward option.  There are other challenges involved which largely overlap with the challenges involved with getting the MX5 box in.  Ratios are very similar though the W58 has a slightly taller 5th. 

Thing is though - I bought two MX 5 boxes for £ 40.  W58s are now north of £ 800 - if you can even find one.....

Decisions :confused:

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Thanks Roger!  Interesting.  Not least because it suggests that a TR4 flywheel is smaller than that the 6 cylinder ones.  My flywheel does not fit in the Mazda bell....... which means my approach has to be different.  I've spoken Vitesse Transmissions to enquire whether they felt like selling me just a front casing, but suspect it is a long shot.

Anyway - I'll be keeping an eye on that.  

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So returning to the MX5 gearbox after the Toyota digression:

I stripped the flywheel and wooden back plate back off and refitted the saloon back plate, flywheel and BW35 bell.  I was then able to offer  up the partly dismantled MX box

This showed that the relatively short input shaft means that the pilot bearing will have to be in the flywheel (normal for the 2000/2500).  I did this for the Vitesse too.  Will get the flywheel machined to take a ball race - probably try to find one with the same OD as the one I use in the Vitesse so the flywheels will be interchangeable..


This means that the tip of the input shaft needs to be flush with the bell front face.  It's 10mm recessed on the Mazda.  THis gave me the dimensions I needed to have proper measure (well, ok, eyeball with steel rule and tape measure).

Then I got a bit carried away.....

Oops......... that's a bit final.....:blink:

Popped on the mill to get a everything flat so I could measure properly......

Mill is a bit small and I have to move the casing 4 times to get everything......... which is not ideal, but eventually I get it flush with the machined surface in the centre, 155mm shorter than it was. 



As the input shaft tip is 145mm from this face and the BW bell is 144mm face to face, this is actually where I want it - except I'm planning to weld an adapter ring to the gearbox casing and bolt the bell to that so I'm going to need to take another 10 - 15mm off to accommodate that.  Though not at the bottom as we'll be through to the oil if I do that there so my ring might be more of a horseshoe......


Incidentally, fun (but useless) fact for the day - MX5 input shaft bearing has the same dimensions as the main drum bearing in a Bosch Classixx 1200 washing machine......

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So question for anyone who has a Vitesse/GT6 gearbox kicking about and accessible to the tape measure.......

I could do with the dimension from the engine face of the bell housing to the gear lever pivot centreline.  (It’s around 560 ish I think, but need moderate accuracy!)

Also the dimension from top face of the remote (where the gear lever pivot ball sits in) to the output flange centreline.


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Hello Nick


I just found 2 x 3/16" ball bearings under the gearbox!

Still I have lots of Motorcycle bits in there as well.

I like your milling machine much better than my Chinese one (Envy) Bridgeport would be better but I can dream? (I could afford one one but not sure how I would sneak it in!)


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Thank you :smile: 

585 better than 560..... but TBH getting the Mazda box under about 640 will be a major challenge.....

I was offered a single-phase converted, CNC Bridgeport when Dennis retired.  Was a fair chunk of cash and would have to have been dismantled to get it here and in the garage.

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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 way home and only covered 78 miles in total

Its an old quarry workings at Clee hill by Ludlow


Ps met a man at ice cream shop that said he a Spitty and a TR250 plus more expensive ones but was in something tin roofed modern on a nice day!!! and when I said we usually do about 5000 miles a year in he looked shocked!!!!!



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Nick, did you see the picture of the gearlever setup in the "Chignell minor" TR6? He posted a pic somewhere...  essentially it looked like they had cut the MX5 gearstick about an inch up from the pivot, welded a bit of flat bar to that and brought it forward, then welded the gearstick to that.

From memory of a saloon box in my vitesse, the saloon/TR box has the gearstick is near-identical position to the vitesse box as I used a vitesse tunnel. So it may just work. Of course, you could do a Clive and move he handbrake rearwards. That was easy :whistling:

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  • 4 weeks later...
On 7/31/2020 at 7:55 AM, zetecspit said:

Nick, did you see the picture of the gearlever setup in the "Chignell minor" TR6? He posted a pic somewhere...  essentially it looked like they had cut the MX5 gearstick about an inch up from the pivot, welded a bit of flat bar to that and brought it forward, then welded the gearstick to that.

Sure did.  But that's on a gearbox that has already had the remote moved forward about 120mm ( relatively easy) and there is no room for that extension bar malarkey on a GT6.  No doubt works just fine on a TR5/6, and maybe a big saloon, but does not meet my design criteria. 

On 7/31/2020 at 7:55 AM, zetecspit said:

Of course, you could do a Clive and move he handbrake rearwards. That was easy :whistling:

Yeah... right :huh: some new definition of "easy"  (might be easier than shortening the remote on an MX5 box though)

I'm not moving the handbrake and I don't want to hack up the tunnel/cover (might have to compromise a bit on that one).

So, mechanical design engineer (graduate 1st class no less :smile:) doing a bit of CAD

CAD became this proof of concept / working model


We can actually select gears with this believe it or not.  There is a further development added now (I don't seem to have a picture of this) which defines the gate.  We have yet to come up with a method of preventing the selection of reverse gear whilst looking for (non-existent) 6th.  It's going to be medium tricky doing this nicely in a long-term way but I do now feel it's possible.

Meanwhile, at the other end, some big chunks of aluminium arrived

I have actually got a fair bit further with this but I can't find the pics I thought I'd taken........


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11 hours ago, Nick Jones said:

Sure did.  But that's on a gearbox that has already had the remote moved forward about 120mm ( relatively easy) and there is no room for that extension bar malarkey on a GT6.  No doubt works just fine on a TR5/6, and maybe a big saloon, but does not meet my design criteria. 

Yeah... right :huh: some new definition of "easy"  (might be easier than shortening the remote on an MX5 box though)

I'm not moving the handbrake and I don't want to hack up the tunnel/cover (might have to compromise a bit on that one).



The handbrake move genuinely was pretty easy. I cheated, and used an MGF handbrake (dimensionally identical to the Triumph one as far as I could measure, but comfier grip but importantly better mounting option) also the MGF rear brakes/calipers and shortened cables. A little bit of thought, but nothing difficult to overcome. Saying that, if doing again I would use VW rear calipers as MUCH lighter.

I am liking the progress with the gearbox. Though struggling to envision how the latest iteration compares with the initial "easy" shortened version That is a hint!

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32 minutes ago, zetecspit said:

Though struggling to envision how the latest iteration compares with the initial "easy" shortened version That is a hint!

The Mk1 (NA) MX5 box (only!) has a separate bolt-on remote housing held down to the rear casing by 4 bolts with a single selector rod going forward enclosed by a tube with rubber seals at the end. You can shuffle the whole thing forward by lopping the front of the remote casting off, reattaching to the casing using its rear holes with the front holes in the casing, fashioning a new support bracket to link the rear to the unoccupied rear holes on the rear casing and shortening the selector rod and tube to match. Same principle as the T9 mod but no welding needed.

There are a couple of documented how-tos on the web with slightly different approaches. IIRC one gains 100mm (easy) and the other 120mm which is harder as represents the limit of the “easy”.

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Yes, saw some of those articles when I was considering the future of the Toledo. (more on that at some point)

Could do with a pic with the unmodified box next to the latest version :smile:

All this stuff is interesting, as the T9 box I have is OK, but despite a refresh is still a bit clunky in 2nd and 3rd. I could just put it in for a pro build about 1K. But alternative boxes hold great appeal! (have even though of RX8 six speed, with a longer diff to offset the stoopid first gear)

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