40 replies to this topic

[StraightCut]

Hi all,
6 speed gearboxes, are any available? I been lead to believe Jack Knight Developents are the only available 6 speed gearbox...Does anyone have one they want to part with or know where I can chase one up.... would work well in my special Mini project ...
I know it's a long shot but I can only ask....

[mab01uk]

Some info and photos of JK 6-speed in link below.

 

Jack Knight 16V And 5 & 6-Speed Gearboxes:-

http://www.theminifo...peed-gearboxes/

 

 

You might also like this box from Swiftune but only 5-speed......!!

 

Quaife-Swiftune 5-Speed Sequential Gearbox

http://www.theminifo...ential-gearbox/

Edited by mab01uk, 12 September 2017 - 11:41 AM.

[mini13]

jack knight are gone, I wouldnt touch a JK box as getting parts will be tricky.

 

about the closest is going to be a quaife 5 speed box

 

http://www.theminifo...ential-gearbox/

[Spider]

Trans-X did them as did KG Engineering in Melb.

 

There's a few guys doing them using Bike Gear Sets, apart from being quite useless ratios for a car, they also are a dog box.

 

I don't think there's any currently available.

[Ethel]

It'd have to be quite a special Mini to run an A Series and need 6 cogs. Taking into consideration the weight, rpm and speed ranges a 4 speed Min that tops out not far north of 100mph will be as well equipped as something weighing twice as much, using half as many gears again to go half as fast again.

[r3k1355]

IIRC there were always issues with Jack Knight boxes being weak?

 

KAD do a 5-speed box.

[StraightCut]

Thanks for the replies fellow Mini addicts..., yes that is a lot of gears but this roadie has its weight down to about 650kg, well trying my best to reach that, running low profile tyres with a Diameter of about 520mm, and a very low 4.2 diff, so a 5 speed is a minimum, 6 speed would be great..
As per strength, some time ago i have spoken too and seen a racer with one... look bullet proof to me, and the Race Mini had some stick too.
Love the idea of the 5th and 6th located on the other side of the pinion gear.

So pretty interested in one, I know it won't be cheap.. but want to find one...

So if anyone knows of any, I'd be happy to hear from you...

[nicklouse]

those are big tyres compared to standard Mini tyres.

 

weight is nothing special.

 

and the 5 and/or 6th may not be over driven so will not give a higher top speed. some will but most are more likely to be still a 1:1 output so you can have a better selection of gears for the corners on a race track.

[Orange-Phantom]

IIRC there were always issues with Jack Knight boxes being weak?

 

KAD do a 5-speed box.

Absolute Rubbish!  The Jack Knight 6 Speed (Dog Box) is pretty much bullet proof.  I know a few people who have them and race with them.  (I have one myself, and no I'm not selling it).

 

The KAD 5 speed box is not overdriven in 5th i.e. 5th is 1:1.

[Dusky]

IIRC there were always issues with Jack Knight boxes being weak?
 
KAD do a 5-speed box.

Absolute Rubbish!  The Jack Knight 6 Speed (Dog Box) is pretty much bullet proof.  I know a few people who have them and race with them.  (I have one myself, and no I'm not selling it).
 
The KAD 5 speed box is not overdriven in 5th i.e. 5th is 1:1.

My dad broke one once, iirc it had something to do with a misshift after he fitted a quickshift. But its 10 years ago and I was quite Young then 😁

[nicklouse]

 

 

IIRC there were always issues with Jack Knight boxes being weak?
 
KAD do a 5-speed box.

Absolute Rubbish!  The Jack Knight 6 Speed (Dog Box) is pretty much bullet proof.  I know a few people who have them and race with them.  (I have one myself, and no I'm not selling it).
 
The KAD 5 speed box is not overdriven in 5th i.e. 5th is 1:1.

My dad broke one once, iirc it had something to do with a misshift after he fitted a quickshift. But its 10 years ago and I was quite Young then

 

again JKD made different types of gearbox. syncro, involute dogbox and, dogbox.

[StraightCut]

Going by the literature I have collected and again to the Racer I spoke to a few years ago, 5th and 6th is definitely an overdrive, will need to find the paperwork to see exactly what the ratio was.

Yes 13" tyres are big, with low profile tyres...hence the low diff ratio.... and hopefully one day a 6 speed JKD G/box.....

[Orange-Phantom]

 

 

 

IIRC there were always issues with Jack Knight boxes being weak?
 
KAD do a 5-speed box.

Absolute Rubbish!  The Jack Knight 6 Speed (Dog Box) is pretty much bullet proof.  I know a few people who have them and race with them.  (I have one myself, and no I'm not selling it).
 
The KAD 5 speed box is not overdriven in 5th i.e. 5th is 1:1.

My dad broke one once, iirc it had something to do with a misshift after he fitted a quickshift. But its 10 years ago and I was quite Young then

 

again JKD made different types of gearbox. syncro, involute dogbox and, dogbox.

 

Yes very true!

 

The involute 6 six speeds were very strong.  I do recall the 5 speed syncro boxes could be a bit problematic with the syncro's.

[Deathrow]

Going by the literature I have collected and again to the Racer I spoke to a few years ago, 5th and 6th is definitely an overdrive, will need to find the paperwork to see exactly what the ratio was.

Yes 13" tyres are big, with low profile tyres...hence the low diff ratio.... and hopefully one day a 6 speed JKD G/box.....

 

Have you not visited the topic mab01uk linked? http://www.theminifo...peed-gearboxes/

The brochure includes a list of the gear ratios from all the different flavours of the JK 5-speed box.

I think you'd be very lucky to come across a 6-speed JK box these days, the brochure states that JK designed a custom gearbox casing to make it work.

Can you explain why you want 6 gears? I'm not sure I understand what the weight of your car and the diameter of your wheels means for needing more ratios when the end points are largely in the same ballpark. Or are you planning an engine with a very narrow power band?

[mab01uk]

There was an interesting 7-page article in the August 2017 issue of Miniworld magazine on the development of the ERA Turbo Mini's, including some interesting background on the 'almost' development of a Rover production 5-speed gearbox for the Mini......

ERA were concerned that the extra torque delivered to the standard gearbox had already caused idler gear and other problems in the Metro Turbo. ERA solved the idler gear problem with a Jack Knight modification but Rover insisted under their warranty terms on limiting the engine torque to 90lb/ft which meant performance was not as scintillating as the original raw ERA prototypes had demonstrated. Rover provided ERA with a copy of their test schedule they had formulated for the Mini, one of the tests was to drive in reverse for 2 miles at 35mph. Rover said this was because the cars they had sold to the Police would often have to reverse for long distances down motorway hard shoulders. ERA took six standard Minis on loan from Rover to Bruntingthorpe aerodrome to put Rover's reversing theory to the test......however all the standard gearboxes broke and it later transpired that Rover had almost never managed to get a car past the test they'd set!
Jack Knight was part of ERA at this time so a 5-speed JK gearbox was tested in the ERA Mini and found to be superior to the standard 4-speed. Despite this Rover management declined investing money on the tooling for a production 5-speed box as the Mini was thought to be nearing the end of its life under Rover plans in the late 1980's (pre-BMW takeover). ERA engineers were confident it could be done with modest investment, they even proved this by secretly modifying a factory production casting die with the aid of the helpful Rover production line staff on the night shift, this produced suitable blank gearbox casings, proving Rover could have done the job for only a few pounds more than the standard box. In retrospect a five speed box would also have updated and transformed the original Mini and Metro but it seemed Rover management at the time possessed very little imagination and were reluctant to invest for the future. Delays in getting parts from Rover and dies for the gear case, meant that the ERA Mini was launched with the standard 4-speed box although some ERA Minis were retro-fitted with the JK 5-speed box.

Edited by mab01uk, 13 September 2017 - 07:30 PM.