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Possible support NC 6 speed gearbox #639527
23/05/20 02:24 AM
23/05/20 02:24 AM
Joined: Sep 2009
Posts: 5,056
Köln Germany
Heinz Online content OP
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Heinz  Online Content OP
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Joined: Sep 2009
Posts: 5,056
Köln Germany
Actually I wanted to surprise you with the result, but it is probably more difficult than I thought. That's why I need your advice.
I have a 2014 4/4, and unfortunately you can't easily switch the final ratio. There are no other gears/teeth that can be changed easily. Williams and Techiques have confirmed it. I would need a complete new rear axle but that is not adequate in price. Not that my car is a slow driver. Everything is very good, the power-to-weight ratio is correct. But on the B roads where she is in her element it would be simply nicer if I could use more of the full revs out of the curves.

So I had a new idea. I'm thinking about to swap my MX5 NC 5 speed against a NC 6 speed gearbox. In this case the first 5 gears come closer together and the sixth gear is almost comparable to the fifth gear of the old gearbox. It is by calculation the same effect than to swap the 3,73 final ratio against a 4,1 final ratio, but in this classic case the cruising gear for the Autobahn is gone, and as seen above another gearbox would be the only way to make a reasonable change anyway.

Here you can see how it works in the MX5 NC. Left is „our“ 5 gear but with a final 4.1 ratio. Right is the 6 speed with „our“ final 3.73 ratio in the Mazda as well. But the Mazda has smaller diameter in wheels.

[Linked Image]

And as the diameter of our wheels is bigger, there is no fear the final ratio would be too short at all.

So much for the wonderful theory. But the practice seems much more difficult. On the Mazda, the hose of the clutch pedal is attached to the bottom left of the gearbox in the direction of travel. But in my 4/4 it is attached at the top on the right side in driving direction. To make it even harder there are additional parts from Volvo to make it fit (you can see and read it written on the parts). Additionally it looks like new openings in the NC 5 speed gearbox are cut out at this place. In other words, Morgan did not make the conversion easy, and we can be thankful that Morgan did it with all the effort to get us an NC gearbox.

There is another aspect to be added. Is the 6 speed gearbox similar on the inside so that the Morgan conversions can be done there? Maybe there is perhaps not enough space inside the 6 speed gearbox? because some of the mechanical parts that are mounted outside the Mazda seem to have moved inside the gearbox.
Conversions on the outside like other mounting points are simple things in comparison.
Also the adapter plate between Sigma engine and Mazda gearbox can be easily attached to the new 6 speed gearbox. The outer dimensions are the same. But the inner ones?

So if someone has experience, I am grateful for all instructions




'14 4/4 graphite grey
Re: Possible support NC 6 speed gearbox [Re: Heinz] #639535
23/05/20 06:59 AM
23/05/20 06:59 AM
Joined: Feb 2016
Posts: 2,623
East Harling, Norfolk UK
Richard Wood Offline
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Joined: Feb 2016
Posts: 2,623
East Harling, Norfolk UK
This conversion was briefly discussed for the M3W which having a relatively narrow power band would, despite its light weight, benefit from a closer set of ratios. I think the issue was width of the 6 speed box though. Not sure how that would affect a four wheeled Classic.

Last edited by Richard Wood; 23/05/20 08:21 AM.

Richard

2018 Roadster - Red/Magnolia - "Morton"
1966 Land Rover series 2a SWB
1960 Velocette Venom
Re: Possible support NC 6 speed gearbox [Re: Heinz] #639553
23/05/20 08:07 AM
23/05/20 08:07 AM
Joined: Sep 2016
Posts: 331
Chester, UK
Grumpy2 Offline
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Grumpy2  Offline
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Joined: Sep 2016
Posts: 331
Chester, UK
I can offer another snippet of info as an owner of two MX5s both with 6 speed gearboxes.

Theres a well documented weakness with the 6 speed box having an very notch shift between gears 1 and 2 particularly when cold.

I'd suggest trying an MX5 to see if you can get on with it. You will certainly not get fast and smooth changes in those lower gears.

Gary


94 plus 8 in Westminster Green - I think!
Re: Possible support NC 6 speed gearbox [Re: Heinz] #639586
23/05/20 09:23 AM
23/05/20 09:23 AM
Joined: Sep 2014
Posts: 1,594
London
MOG 615 Offline
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London
Morgan enthusiasts over the years have always tackled projects like this , so if you feel you have the resources to make it work then I am sure it would give you a lot of pleasure (and not a small amount of pain!)

However , you mention that a new axle is "not adequate in price" . I would estimate that changing the gearbox , especially for a first time ever would be MUCH more expensive in both time and money.

As Gary says the 6 speed box does not have that wonderful "rifle bolt" action of the 5 speeder, so you would lose one of the better features of the Sigma/Mazda box drivetrain. I would plug into the M3W discussions and follow those up initially. There are some very worthy and experienced engineers out in that community who can almost work miracles.

Last edited by MOG 615; 23/05/20 09:27 AM.

Andy G
1999 +8 , Indigo Blue.
Ex-John McKecknie/Mike Duncan 1955 +4 racer.
Re: Possible support NC 6 speed gearbox [Re: Heinz] #639592
23/05/20 09:32 AM
23/05/20 09:32 AM
Joined: Sep 2009
Posts: 5,056
Köln Germany
Heinz Online content OP
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Heinz  Online Content OP
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Joined: Sep 2009
Posts: 5,056
Köln Germany
Thanks Richard, I will try to find the M3W thread. The text below, re Gary, is about the 6 speed characteristics. So I know, there are so many conversions in the Mazda NC world, e.g. you have to sacrifice one of three bolts for the starter mounting etc.

What I need to know is, first at all of course will the 6 speed fit into the 4/4 but secondly also, what in all did Morgan already to change re the 5 speed to make it fit and work in the 4/4. This should be measures I have to do with the 6 speed as well anyway (if it fits in size).



Thanks Gary. Regarding the smoothness I would be fine with the NC 6 speed. My son has a beautiful NA. He has installed an NA 6 speed himself, and it is very good. A little tighter maybe, but very defined. I have read many German, US, UK Mazda forums. My summary is that quite a few people share the problem with the 6 speed that you describe, Gary, and secondly, that you cannot shift into first gear before tight hairpin turns until the car is stationary. This is what people report with a converted 6 speed as well as others with original 6 speed from the beginning. But I would accept it this way if I have a more vivid drive in 2th to 5th gear. People recommend to chose a NC series 3 or series 3.5 gearbox.
As a counter-argument it seems that often at 6 speed the clutch opening travel was wrongly adjusted. There are some reports where the opening travel was corrected (further up) without the closing force decreasing when the pedal is released. But the ease of shifting increased.
There are even post claims that even the garages and sometimes even Mazda itself have set the 6 speed too little opening, and that's why it has its reputation. If I can't shift into first gear while driving, it doesn't matter with the newer shorter second gear.


'14 4/4 graphite grey
Re: Possible support NC 6 speed gearbox [Re: Heinz] #639599
23/05/20 09:45 AM
23/05/20 09:45 AM
Joined: Sep 2009
Posts: 5,056
Köln Germany
Heinz Online content OP
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Heinz  Online Content OP
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Joined: Sep 2009
Posts: 5,056
Köln Germany
Andy, I just saw your post. A diff ratio conversion as it would be possible until ca. 2011 MY or so in ca. was around 1.600 GBP, but a new complete BTR rear axle with a 4,1 ratio would be more than 6.000 GBP. If I find a good in shape low milage NC 3.5 6 speed box, it would be ca. max 800 € (best from a donator car with a crash, where it is still built in to check it).

If it should work out to be possible to change it, it would be a winter project 600€ to 800€ to spend plus a lot of pain for free, and surely some unspeakable curses smile


'14 4/4 graphite grey

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