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my new gearbox? (Mazda MX-5 to TR)


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Ups, the adaptors are already delivered, I'm really surprised about the laser cut surface! Tomorrow will be first fit, please keep fingers crossed for me.  

Thanks Russell and Andi, thank you very much, all worked well, fit was 100% on first attempt, the 8 mm drills are exaxtly to the point they have to be for the 5/16" bolts! Btw, the bar is on

Talking of gearbox changes, back in the 8o`s when I was involved with Jaguar racing we converted a V12 XJS from a GM 400 auto box to a Cosworth T6 manual 5 speed by a cut and shut of the two bell hous

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Good evening everybody,

about 1 kg is off the gearbox tail

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You might remenber this photo

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Finally I made a modification to this, sadly I cut through some blowholes...

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You have seen on this photo how the gear box body will touches the frame

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This will not be the case anymore

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Ready to clean, this was a short chapter (but I have to do other modifications on the front end).

Ciao, Marco

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from the ordered aluminium I made this tube,

the o-rings are also in but sadly I ordered the wrong size.

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So today I cleaned the gearbox tail and put the selector shaft in pieces.

It is fulcanised in the upper solid metal piece, looks so harmless but was an anoying job.

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Also I did a thread repair on the speedo drive.

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This should work

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ready, waiting for the seals

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Before I bolt it together I hope for an answer from Mazda:

I asked them for the availability for "TR"-suitable speed cogs: 1 turn of the shaft must be 0.4 spins of the speedo cable.

Ciao, Marco

 

 

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Hi Marco, Having no practical engineering experience, It has been very interesting following your project. +1 for the pictures helping us novices. Keep them coming and as for the "wrong o rings " I call them no rings the amount of time I have got the wrong ones :wacko:

 

Paul

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Hi,

the o-rings have been in yesterday and to be prepared for your enquiry I ordered 6 sizes, each a minimum different.

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I chosed the ones which give a reasonable tight fit.

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I painted the steel plate black and had to cut a bolt shorter.

The next photo may be a help for those who have problems to make an already short bolt more shorter on the grinder bench.

A short piece of steel with different sizes of threads is a great help, locked with a nut you can work on the vise.

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All bolts locked it fits and the selecotor shaft still slides without friction.

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Final check (with a M6 bolt in) before I press the roll pin in its position:

- can I assemble the tail on the gearbox - yes

- is the shifter upright in both directions (forward and sideward) - yes

- do I get all gears in - yes

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That's it for today, sadly my wife gave me some other challenges....

Ciao, Marco

 

Edited by Z320
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Time for assemble, this is the shifter lever with a new gaiter.

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For some of you might be interesting what is inside this housing.

From the left a spring loaded piston with 3 positions / 2 steps, with no gear in it holds the lever in the N position between 3 and 4.

To move to N and 5 you have to press against it, for R some more. Against the steps is to load of a sping loaded steel ball from the rear.

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Inside you see a pin and a wing on the "shifter block", this allows not to shift from 5 to R,

to do this you have to press the lever against the piston and spring loaded ball in the position R.

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From the left side there is a cover with a spring loaded pin, this holds the lever also in the position 3-N-4,

to move in 1-N-2 you have to press the "shifter block" against the pin, the sping inside is the weakest of all 3.

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The sealant on the cover is "Dirko grau" (silicone), I love that, it's "not visible" on aluminium.

Last time left side, responsible for 5-N and N-R

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right side for 1-N-2

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Very polite of this Japanese engineers: you cannot mix the parts, each ones position is self explaining.

Oil channel to the rear bearing is in again, tomorrow it will move back on the gearbox, than see what comes next.

Ciao, Marco

Edited by Z320
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Those @!"&%$!!@ Japanese engineers!

Yesterday I failed with fitting the tail on the gearbox and was afraid of dismantling all what I fixed.

From the MX5 manual (online) I know how to put the tail off - it should be easy to put it back the same way?

But there is no description about that.

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Yesterday it did not work and I have been real desperated,

so today - with a lot of patience - I had a very close and long look....

Best was to put the shifter lever, springs and pistons off to get the nose on end of the shifter shaft

as much "down" in the position of the 3-N-4 fork, then slide the tail down and twist the nose it anti-clockwise.

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This is only possible with the shifter block in the R position.

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Ready, this is the position

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last look through the gap to the nose and forks

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Slide it down, twist it anti-clockwise, the nose will match in N between 5 and R, match the dowels, 5 mm more down -  ready.

Knowing this and after practicing it some times this is only a 5 seconds job, tomorrow with sealant.

Ciao, Marco

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Hi there,

all was assembled and the shifter working well, when suddenly the gearbox sticked in R!

No way to get it work, so I had to put the tail of again and found the forks in this position:

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R is in and the nose on the selector shaft probably in the O marked position, shifting back to R not possible.

OK, I did all a second time, tested the shifter, worked well ...then suddenly sticked in R again, @&%$!!@ - tail off one more time.

A serious problem, at the German MX5 forum no anser to my question,

but Youtube is my friend and Mike the Miata King told me all about the gearbox sticks in R.

So what can we all learn from this for our daily life,

keep it always in our mind and best write it in big letters on the wall of our garage?

NEVER SHIFT A MX5 GEARBOX ON REVERSE WHILE THE REVERSE SWITCH IS NOT IN!

Ciao, Marco

 

 

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So now I continue with modify the gear box housing.

The part above the red line has to be cut off (will touch the bulkhead) but first the left hole has to be drilled through.

This must be for a dowel on the MX5 engine?

qrcvDtTiMjDucPm2k-KSGyUtBOZTglUcqYsuiTw1

When I made the adapter plate I realizes I have to do this because the next drill left of it is to close to a TR stud.

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Here on this offset the drill should come out - this surface later I have to level.

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A plug drilled 9 mm helps to guide the 9 mm drill

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KMV0UZA863wCQdK_PnojI6PCVYZtu_w5SNNZlAiY

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Next I used a M8 x 9 x 15 mm flat countersunk drill to level the surface

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Space enough to use a M10 x 10,5 x 18 mm flat couthersunk drill and drill the hole up to 10,5 mm (bolt will be 3/8" UNF)

Ciao, Marco

 

 

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14 minutes ago, Z320 said:

So now I continue with modify the gear box housing.

The part above the red line has to be cut off (will touch the bulkhead) but first the left hole has to be drilled through.

This must be for a dowel on the MX5 engine?

qrcvDtTiMjDucPm2k-KSGyUtBOZTglUcqYsuiTw1

When I made the adapter plate I realizes I have to do this because the next drill left of it is to close to a TR stud.

S6L1fzTep3_M53vt0uxz-BesQAzoRDh0wB_Rn3N7

Here on this offset the drill should come out - this surface later I have to level.

QZfniQpVdiqpfmNJzlyU1iwz2eyFYMF9MniANxYq

A plug drilled 9 mm helps to guide the 9 mm drill

ixpJ9Rl8NNoNwdGoYYuDipRX04VpHHru4kyx47Bw

KMV0UZA863wCQdK_PnojI6PCVYZtu_w5SNNZlAiY

54MaAPrOpi_wrQaRBAPQx6fWOAMJfsSvnsecZkeD

Next I used a M8 x 9 x 15 mm flat countersunk drill to level the surface

U1IxqdKJR1-1HoywbYRLdylZDWjUY06TrQdH31ty

Space enough to use a M10 x 10,5 x 18 mm flat couthersunk drill and drill the hole up to 10,5 mm (bolt will be 3/8" UNF)

Ciao, Marco

 

 

Why drill 10.5 mm for 3/8" bolt when 3/8" is 9.52mm?  For me that is wobbly.

Peter W

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Hi Peter,

I do this because you can get the flat countersunk drill M10 only with 3 pin sizes:

- 8.5 mm (to cut a thread)

- 10.5 mm (small gap to M10)

- 11.0 mm (wide gap to M10)

What do you recommend?

I could make a bush 8.5 mm x 9.00 mm and use the 8.5 mm one, later drill 9.5 mm...

Ciao, Marco

Edited by Z320
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