More 5-speed waffle... MX5?

Willy Eckerslyke

Well-Known Member
I'm still in the thinking stage of a 5-speed conversion for my 2000TC and noticed that Mazda MX-5 gearboxes are extremely cheap and plentiful. Just wondered if anyone knows anything at all about them? They appear have a good reputation for longevity and a superb gearchange and are very compact though the bellhousing looks very long. As far as I can see from photos on the web, the bellhousing is removable - need to confirm this though.
The gearchange looks to be a single rod type which should allow its position to be modified if necessary.
Any thoughts?
 
We always used Supra boxes back in the day on V8s, as they could easily handle the engine..
 
Yes I realise that Supra boxes are ideal, but they're also scarce and expensive in the UK. So I'd pretty much decided on an LT77 or R380 until this idea popped into my head. :)
While I doubt if an MX-5 box would be strong enough for a V8, they are able to handle a 1.8turbo while being raced, drifted and generally abused in the Mazda so I'm thinking it ought to be strong enough for a 4-pot P6, though the Rover is 200-300kg heavier.
 
I've had an MX5 box on the bench and I'm not convinced it would be a good swap. The bell housing is cast complete with the gearbox casing so any adapter plate would be quite big. Also there's no tail shaft - the propshaft has a splined end and slides directly into the gearbox so you'd need to make some sort of hybrid propshaft.

The power characteristics of the 1.8 MX5 engine are similar to the TC engine so that side of things will be fine.

It's a nice gearbox though so it would be good to see if you can make it work.
 
Ah, thanks for that. Whether the bellhousing is removable or not is the main thing I couldn't confirm by searching the web. Sounds like a non-starter then...
... unless I also fitted the Mazda engine to go along with it! (don't worry, I wouldn't dream of such a thing.)
 
Nice idea. Spent a lot of time driving my mother's Mk1 MX5 and it is a delight.

Hasn't the Ford Sierra box been done in the 4cyl before?
 
Willy Eckerslyke said:
Ah, thanks for that. Whether the bellhousing is removable or not is the main thing I couldn't confirm by searching the web. Sounds like a non-starter then...
... unless I also fitted the Mazda engine to go along with it! (don't worry, I wouldn't dream of such a thing.)

It might be possible if you could make a new back plate for the engine block.
 
PeterZRH said:
Hasn't the Ford Sierra box been done in the 4cyl before?

Yes. The guy I bought my (as yet unfitted) LT77 four pot conversion kit from had fitted a type 9 to his car & he was very pleased with it.
 
One reason for my confusion about the bellhousing was this post where someone's talking about splitting 2 types of Mazda gearbox:
http://www.locostbuilders.co.uk/viewthread.php?tid=191454
Perhaps it's the RX8/RX7 that has a removeable bellhousing?

Ford Type 9 'boxes are getting scarce and sought after now I believe, so no longer a cheap option.

I wondered about the BMW E30 'box too, but after measuring the similar one in my E28, decided that it would be too much of a squeeze.
 
It looks like the 6 speed ones have a more conventional separate bell housing arrangement.

No one ever seems to mention using Vauxhall Omega engine and gearboxes for for transplants, but the specs look quite promising.
 
testrider said:
It might be possible if you could make a new back plate for the engine block.

Hi, yes I thought that, They both have 8 1/2" clutches so the next problem is would the Mazda
bellhousing go over the Rover flywheel?

Colin
 
The Rovering Member said:
PeterZRH said:
Hasn't the Ford Sierra box been done in the 4cyl before?

Yes. The guy I bought my (as yet unfitted) LT77 four pot conversion kit from had fitted a type 9 to his car & he was very pleased with it.


I bet. Much nicer than the LT77 (IMHO).
 
Hi, Like type 9s Omega boxes are scarce and expensive because they are used behind Saab
engines in RWD conversions.

Colin
 
testrider said:
It looks like the 6 speed ones have a more conventional separate bell housing arrangement.
Hmm, food for thought. Except that I'm not a fan of 6 speeds, and these have a lower 6th than the 5 speed's 5th according to one page I read.
testrider said:
No one ever seems to mention using Vauxhall Omega engine and gearboxes for for transplants, but the specs look quite promising.
They last well too - my mother's estate did 470,000 miles!
But if they're anything like the Carlton, the 'box is seriously big and heavy.
 
colnerov said:
Hi, Like type 9s Omega boxes are scarce and expensive because they are used behind Saab
engines in RWD conversions.

Colin

Really, that's interesting! Last time I looked you could pick up a 2.2 Omega manual for about £600 which doesn't seem to bad for a decent engine and box, particularly if there's money to be made from the rest of it. But if they're a big ole lump then it's probably not worth it.
 
You know, perhaps the 6-speed MX-5 'box would be OK after all - if I swapped the diff for one off a V8. I.e. dropping the final drive from 3.54 to 3.08.
That could make for quite an interesting combination even if 6th was only used on special occasions.

Shame the 5-speed's unsuitable though. When I said they were cheap, I hadn't even spotted this listing:
http://www.ebay.co.uk/itm/121253041658 Clearance price of £19.50 complete with a warranty. What! :LOL:
 
Just a quick observation on the MX5 5 speed 'boxes, the pinion sits behind the bellhousing lip unlike most Rover gearboxes where it protrudes, and the bellhousing tapers in almost immediately where the Rover flywheel needs a straight section for clearance assuming they are of comparable size? Be warned with the 6 speed 'box, most modern gearboxes that I've seen don't have removable bellhousings, they often have seperate front and middle/rear casings, but the front section is generally more integral to the gearbox unlike the original 2000 type gearbox had.

Honest opinion is you need to start physically comparing any possible donor gearbox with an original side by side, beyond that it's just uneducated speculation.
 
As the owner of a '90 MX5, they are very nice gearboxes to use - a nice smooth shift.

That said, the gear ratios of my MX5 really wouldn't suit a P6. You'd need to ensure you have a suitable diff ratio as otherwise you'll quickly be frustrated with it on the motorway - I don't know how the 2000 diff ratio compares to the MX5.

I think the 6 speed boxes have lower (i.e. more revvy) gear ratios than the 5 speed, so would need an even taller diff. The 6 speed box MX5s already came with a higher diff ratio than the 5 speed to compensate, and have a similar overall ratio to the 5 speed in top gear.
 
sowen said:
Honest opinion is you need to start physically comparing any possible donor gearbox with an original side by side, beyond that it's just uneducated speculation.
Nail on head there Simon.
Prices of used 5-speeds would have made it feasible to buy one just to experiment, but 6-speeds currently start at around 300 pounds which is a lot to waste if the idea's a no-hoper.

Tofufi, your post about the ratios confirm what I'd read. That's why I mentioned moving to a taller diff off a V8 P6.
 
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