6-Speed Gearbox

[Ianashdown]

Not wanting to hijack staggmatt’s thread on the 5-speed conversion I thought I’d start a new thread.

In a previous life I was a transmission designer for Hewland and I’ve been looking at possible donor ‘boxes for conversion for use in an Elan, or any TC based car. The Ainsin AX6 transmission, used in the MX5, is available new or used and would seem to be a good candidate. It’s more or less size appropriate and offers six-speeds. The ratios can be made to work I believe.

I think it would take a new Bellhousing and Tail casting, but these don’t seem to be too difficult, so just the center section would be used.

These days low volume castings are a possibility and only a few internal parts would need to be made or modified.

I’d be interested to hear the feelings of this group if such a ‘box were available as a no-mod replacement kit. I’m sure there is a price point at which this would be acceptable, but at this time I have no idea of the cost of a new unit, the machined castings, internal parts etc, but I’m willing to initiate a feasibility study to see if it’s viable or not. I realize that there are other potential applications so on the basis of ‘if you build it, they will come’, it might be worth the exercise.

Please let me know your thoughts.

Ian

[Frogelan]

Ian,

Retroford have recently announced a Ford engine to Mazda adapter made from billet aluminium. However, there is no clarity as to which engine or gearbox to my knowledge, but a simple telephone call can probably solve this.

I have no idea as to whether the gearbox would otherwise fit. It would be also possible (I think) to do an inverted extension.

In the research that I have done, it would be also possible to use a ZF 5 speed but these gearboxes are expensive. There is a Burton bellhousing but the starter motor position is on the exhaust side.

Andrew

[Ianashdown]

Hi,

I’ll need to do a cost evaluation in addition to the technical study to truly understand the suitability, or not, and the possible options. The AX6 seems like a good candidate as it’s available new and plentiful used at reasonable cost.

I had a ZF S 5-18/3, which was stolen, and I think it would also be suitable. It is ‘only’ 5-speed and I don’t think currently available new, and as you say, expensive used.

Living in Southern California, freeway use is almost impossible to avoid, so having a nice relaxed overdrive would be very nice.You’d then have 5 gears for the fun roads!

Ian

[Frogelan]

Following my earlier note:

- I could not see the reference on the Rétroford website (but there are other new products missing as well).

- the ZF box is remanufactured by Elite in GB and a firm in Australia. It is, imho, probably the best 5 speed ever made and has motor sport credibility!

- One solution for the fast roads in the US would be a 3.4 diff which are now available.

- It is possible to find the ZF in Europe with less exciting ratios but it is still expensive.

I agree that the reasonable solution is the Mazda box but I think I will buy a S5 18/3...

[Ianashdown]

Are the two outfits building the ZF building a drop-in solution?

Ian

PS. I sort of know Elite. I designed a ‘box for the company when it was Staff Silent Gear Co. Maybe they will talk to me . . .

[alan.barker]

I think there was a 6 speed project with Spyder in the past and Myers that was shelved.
Have a look at past post.
Alan

[alanr]

As Alan says the 6speed Mazda box conversion nearly came to fruition once. Spyder were going to produce the conversion but for whatever reasons it never happend or worked.
All been discussed previously see below.:-
viewtopic.php?f=31&t=33557

Alan

[Frogelan]

Reply for the two Alan's...

I respect what Spider do, however, their CRM is not their strong point!

I will contact Rétroford to see what they are upto. GB Sportswear have a clever external linkage.

A

[jono]

Has anyone considered the Caterham 6 speed? - a lovely box with great ratios.

[RobertMaulden]

Hi,

I’ll need to do a cost evaluation in addition to the technical study to truly understand the suitability, or not, and the possible options. The AX6 seems like a good candidate as it’s available new and plentiful used at reasonable cost.

I had a ZF S 5-18/3, which was stolen, and I think it would also be suitable. It is ‘only’ 5-speed and I don’t think currently available new, and as you say, expensive used.

Living in Southern California, freeway use is almost impossible to avoid, so having a nice relaxed overdrive would be very nice.You’d then have 5 gears for the fun roads!

Ian

This ZF box is available new in the UK (the serious Escort / Lotus Sunbeam rally boys use it) but the last time I looked it was circa £3500 + VAT. Used, they do appear occasionally, but expect to pay circa £1500 (& then the cost of a rebuild)

[gav]

That info about the ZF boxes sounds about right.
I have an old one that I am thinking about fitting back in the sprint. I changed diff ratio to 3.38 which is great for motorways (around 3100 at 70 with the MT75 box) but I am still unhappy with 1st gear on the MT75.
The ratios on my ZF are
1st. 2.99
2nd. 1.76
3rd 1.3
4th 1.1
5th. .874

You do have to be careful with the ZF ratios as some S5-18 boxes have higher first gears. The only downside to me is that I need to cut out some GRP at the top of the tunnel for the gear change housing which protrudes through the tunnel by a good few inches.
Also I have a space frame chassis so it fits in the gap between the outer box section - to fit it into a folded chassis would I suspect require some engineering around the change unit

[gav]

Oops - Just had a look at the Elite site - their S5-18 new boxes are £5,250 plus VAT

[gav]

.......and the ratios are really for rallying starting with first at 2.3 and 5th 1.0

[jono]

For anyone interested in ZF, Wayne Lee is your man (based a few miles from me and probably the World's leading authority - even ZF in Germany call him for advice!):

https://www.motorsporttransmissions.com/home

[innesw]

I would be certainly interested in the project and happy to stump up some costs to be an "early adopter"

What interests me is the choice of gearbox, I have small amount of experience with MX-5s/ Miata's
The 5 speed box is considered to have the better shift (a lovely mechanical snick-snick) I have used both and the 6 speed I personally found shifting into 6th a bit rubbish at first, also not a fan of the position of reverse.
Both can easily handle the power of our little twincams compared to what people torture modified turbo mx5's (200+ hp upwards).

The 6 speed box only offers a slight benefit over the 5 speed in terms of ratios (I would be a little brash and describe it as "2x overdrives" in the 6 speed with the diffrence at 70-80mph being roughly 200-300 rpm over the 5 speed but a benefit in RPMs can't be denied.

Has anyone considered the Caterham 6 speed? - a lovely box with great ratios.

My understanding Jono is that the Caterham Sigma 6 speed is a modified Type 9 i.e. to get shifter in the right place you essentially need to build a Voigts gearbox. (albeit 6 speeds! - maybe, possibly not)

https://caterhamparts.co.uk/194-gearboxes

The Caterham (MX5) 5 speed is what excites me (picked for the good shift), no bellhousing but shifter position on the tail housing would need shortened or a custom tail housing cast, quite a few good threads out there shortening the shifter (these use the early NA mx5 gearbox tail housing).

Below is a thread of one shortened by ~4 inches for an Austin Healy Sprite.

http://the-mite.com/mite18.htm

Another thread shortening by a whopping ~9inches for a ?TR2-3

https://www.tr-register.co.uk/forums/in ... tr/page/6/

Innes