Hi, I find it interesting that you mentioned your 94 transmission has a blue speedo ring gear they are usually yellowy/white for that year in all the transmissions i've seen (they changed in December 1991 as far as i'm aware), we sell the late model speedo ring, see here: https://www.puremr2.com/index.php?route=product/product&product_id=177&search=speedo but maybe you have had a earlier model transmission swapped in at some stage? Maybe there is a possible mismatch between the speedo sub-gear assembly drive cogs and the transmission drive cog if you're running a electronic sender. Do you know the history of your transmission?

miyagi
Should I have to remove the box to repair the speedometer drive gear I'll would much prefer not having to remove the whole motor and gearbox assembly.

Obviously the advantage of doing it that way is that you don't need to disconnect the wiring loom, coolant, and  A/C pipes. A PITA to put all that back, especially re-bleeding the system etc.
 
But to remove the trans with the engine still in the car if you want to do the work yourself you will need to read up on it since it can be a tricky job, depending on what facilities you have. 
 
Things to consider:
First how to safely support the car, then after removing the rear X member suspension and drive shafts, you'll need to work out how to safely support the engine on the passenger side, since you will only have one engine mount left on the driver's side.
IMO a block of wood under the sump on a trolley jack is a risky operation; if it slips - disaster, although I'm sure people have used it. I solved this problem by fabricating a bar across the strut towers so I could securely support the engine from above.

The whole assembly will also need to be lowered slightly on the passenger side so the trans. will clear the chassis to get it out, and transmissions are heavy suckers so you'll need something to raise/lower it unless you have been spending a lot of time at the gym.
I had the use of a car hoist for this job as well as an engine crane, and trolley jack.
Even so it was still a tricky operation, but quite feasible.
 

Before the big pull apart... What state are you in?
Is it worth trying another cluster or new speedo sender unit in case something is dead without obvious signs? If you are in Brisbane I have spares (not to sell just to try)...

TonyMR2,
I am in Perth, Western Australia and very much appreciate your offer, however I have ordered and waiting for the arrival of the gear driver and follower.  Process of elimination should do the trick and hopefully I will have the solution in the near future.  Many thanks for your feedback, cheers Miyagi.

Hi Guys,
Process of elimination has proven successful by the use of an endoscope to establish that the Differential plastic drive gear (blue coloured gear) is the issue.  Safely raised vehicle on rated stands, with assistance operated engine and drive assembly, place endoscope in the speed sensor and viewed on screen only to indicate ovality on differential drive gear.
 
I'm very exited to have successfully removed the complete engine and gearbox assembly (achievable with no assistance, under carport using standard equipment) which I considered a relatively easy task to accomplish as there wasn't too many major obstacles.  A great learning curve and also knowing that removing the whole assembly is definitely the only way to go as it all makes sense to inspect all other components while it is out of the vehicle.
 
I would like to ask for some suggestions regarding repair of the gearbox (E153 Turbo)
1.  Is it achievable at home with some specialist tools
2.  Spend the money and have professional transmission shop to repair ( recommended outlets in Perth, Western Australia)
 
Many thanks to all the feedback you guys have provided and have a great day.
 
Kind regards,
 
Miyagi   

Hi Pure MR2,
In reply to your question regarding history of gearbox Turbo E153 with speedometer issue having blue coloured plastic speed differential gear.
 
Obtained assistance from my friend in locating the gearbox number situated under the clutch fork rubber boot indicated S01104255.  Would you be able to provide additional details with the numbers provided.
 
Many thanks and have a great day
 
Miyagi 

I believe I am good with tools, good with engines, family mechanics. I am mid of two gearbox rebuilds (early and late boxes, new synchros, new lsd, bits and pieces), however the work is being done by someone who I hold very high as to having a professional level of knowledge, experience and skill - who also has some of the specialist tools (custom made). Forever grateful.
Personally a professional is worth the expense/importance of a good gearbox.

With the gearbox out you might be able to inspect any broken teeth on the internal ring.

Why I am posting... Remind me / Pm me if I don’t repost, I have both mechanical and speedo drives (different ends from memory), I have both blue (early model box) and white (late model box) speedo rings (from memory they were different diameters/sat on the final drive differently so are not interchangeable). Before cracking the box and starting down the buy parts rabbit hole of rebuild let me check the parts. Again, it’s only from memory, I can check. Otherwise maybe PureMr2 also has a blue ring to compare size to. If these are different then might be another issue you have.

Tony MR2,
I trust you are in great health and spirit.  I sincerely appreciate your interest and guidance.  I would like to PM you however not familiar on how to do it (is it through Facebook).
 
After an extensive search of the blue plastic differential gear part # 334181-17010 (confirmed to be a discontinued component) worldwide including USA, Canada, Japan, Australia and Russia.  I was introduced to a Japan Auction site by a very knowledgeable and trustworthy MR2 enthusiast friend of mine.  Very fortunate for me I managed to win a brand new blue plastic gear matching part #.  Since then I noticed that another gear is now on auction for an additional 7000 yen from a different seller.
 
Thanks to both you and my friend to confirmed that the two gears are of different dimensions.  My friend informed me that the E153 turbo box I have is a November 1990 build, which as you have mentioned blue plastic gear for the earlier model box.  PureMR2 has also kindly assisted however they only have the white gear available at a half the price (great if it was white).
 
Thanks again for your interest.
 
Miyagi       

I checked the mechanical and electronic speedos for consistency in length / speedo gear width and teeth - both being the same only that the electronic speedo gear shaft is longer (longer as in a sitting inside the speedo sender, however depth of the speedo gear inside the box is the same on both). So both mechanical and electronic speedo senders (gears) should not cause any compatibility issues regardless of the inside ring colour.

I couldn’t find the blue ring to compare to the white however from memory different mounting as in can’t be swapped (couldn’t use my old non lsd early model speedo ring with lsd diff - had to buy the white).

Process of elimination, if you have tried, swapping the cluster, swapping the electronic speedo drive unit, tried spinning your speedo drive gear with a drill and output is consistent at a static speed, that would support the look into the gearbox.

But if guidance. Gearbox rebuild parts ordered last year, basics: seals, bearings, square bushing, drain bolts, selector boot (basics to rebuild / refresh, not including any synchros etc) with postage was $300+

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