Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Mazda gearbox convertion

Hi, I'm thinking about getting rid of my old 4 speed gearbox from my old plus 8 for a Mazda 5 speed convertion from vittese. Has any one had one fitted ? Can you tell me how it is, any information would be good. Is it worth the £3000 ??

If you’ve got a Moss Box you’ll make it less valuable . If you don’t like the gearbox I’d swap for a more modern Plus 8.

No it's not a moss it's the rover 4 speed box and it is not in good condition

Rory, I recall you saying 4 years ago that the car was your parents' car, much loved an one of the Plus Eight Lightweights.

As there were only 19 (if my memory is correct) of these cars produced, I would consider carefully a change of gearbox, particularly a non-Rover gearbox as it may undermine the car's value.

An additional consideration is that you mentioned to me in 2013 that your parents bought the car new.

Obviously, it is your decision as to how you wish to deal with the gearbox but thought that I'd respectfully offer some thoughts.

Finally, I converted my 1976 Plus Eight from a Rover 4 speed to a 5 speed in 1988 and am happy to guide you through the changeover.

Obviously the car is for driving, not a museum piece. The Mazda box is fabulous.

I would change it, and keep the old box and all the bits to convert it back if ever you decide to sell it to a collector. In the mean time keep the car driveable and enjoy it.

Just my thoughts on the subject.

There are a number issues to consider before embarking on a change of gearbox.

1) Originality and whether this is important to you now or potentially in the future especially if your Plus 8 is one of the 19 Lightweights.
2) your wheel size and whether you are running on 5.5J 15" wheels or the 14" Millrace wheels that were introduced for the 1975/76 Lightweights and 1977 onwards 5 speed Plus 8s; the LT77 allowed smaller wheels and lower profile tyres whilst allowing the tyre rolling radius and therefore overall gearing to remain more or less the same as the earlier 4 speed cars.
3) the distance from the bellhousing to the gear lever position; note that the Mazda gearbox conversion is aimed at MG Bs and both 4 and 8 cylinder cars used the same all-syncho 4 speed gearbox (Dave W, can you confirm?) and this is not the same gearbox as the Rover V8 4 speed gearbox.
4) clearance to the handbrake lever may be compomised as the lefthand side of the Mazda gearbox is bulky and may cause fitting problems.
5) potential mounting issues although your car will have a variant of the 5 speed chassis and this together with the centrally mounted clutch slave cylinder should mean that this part of the changeover may be relatively straightforward.
6) a new gearbox mounting will have to be welded in.
modifying the handbrake lever mounting (necessary for the LT77/R380 and almost definitely required for the Mazda 'box.
7) modifying or re-making the gearbox tunnel cover together with associated re-trimming bearing in mind that this could add a lot of cost to the project.

You may find it easiest to go down the LT77/R380 route; second would be to consider the Borg Warner/Ford T5 gearbox as fitted to Ford Cosworth Sierra, Mustang and TVR - there is a lot of experience with this gearbox in competition and it is renowned for its torque capacity. None of these may have the sweetness of gearchange in comparison with the Mazda 'box but bear in mind that your Morgan is over 40 years old, has a relatively slow revving V8 but will pull the socks off more modern engines.

You may find the following link useful but note that the thread only starts at the beginning of 2017:

http://www.v8bb.co.uk/viewtopic.php?f=2&t=918

There appears to be insufficient experience to comment on the longevity of the Mazda 5 speed gearbox combined with the Rover V8. Bear in mind that it is low down torque that destroys transmissions rather than brake horse power.

Finally, don't necessarily write off your 4 speed gearbox, they are more than adequate particularly if the engine is relatively standard and especially if maintained with modern synthetic oils.

Did the swap and car drives much, much better with the Mazda Box. No strings attached but Vitesse gave me great service. just do it.

Out of interest Paul, what model and year did you undertake the conversion?

I agree absolutely.

Fit the MX5 box, then clean up all the bits needed to fit the Rover box, perhaps even get a re-conditioned Rover box if the original is beyond repair, and keep for the fastidious collector who might want to convert it back.

Is the MX 5 box strong enough? As has been said, torque is the issue. Well, the MX 5 box is the one bit of the M3W transmission that doesn't seem to fail...
Talking to my MX5 obsessed pal he says that the box will take 200 ft/lbs for ever and up to 300 ft/lbs if not thrashed.

How much torque does the Rover V8 used in the car produce? I'd guess no more than 250 ft/lbs. So it should be fine.

Hi yes it is my dads old car, it is a lightweight 1976 ( R8066) you have a good memory?