15 replies to this topic

[DaveGrohl99]

I Presume im not the first and wont be the last in a classic mini who wishes they had a fifth gear!
My car is a 1293 and highly tuned it flys trough the gears but is screaming for more in 4th.
A 5th gear box is unbelievably expensive so I'm asking about a different route of changing the ratios !
What would you guys suggest and whats the best cost effective way to go about it ?
All help appreciated!!

[nicklouse]

Well as most 5 speed boxes are still 1:1 you would gain nothing other than having more gears to change through. (Yes some have overdriven 5th)

Change your final drive ratio to give a crusing revs thst you want.

What FD do you have now?

[DaveGrohl99]

I don't know thats the problem !

[Midas Mk1]

What's the revs at 70 in 4th? Use the guess works calculator to find out, 3.2 /3.1 is a happy medium.

2.7 kills all performance but is nice for sitting at 80 all day long, but even with that its never gonna be like a modern cruiser.

[DaveGrohl99]

4-4.5 revs

[Cooperman]

There is no easy answer to the problem of gearing with a classic Mini.

If the engine is 'highly tuned', that is it is very modified to give more power, then the power band will be narrower than standard, so wider ratio gears are not an option.

Remember, you are driving a car designed about 60 years ago and gearing was for the driving conditions back then.

4000 rpm at 70 mph is not at all bad for an old car ad an A-Series engine will cruise at 4000+ rpm all day long with no problems.

The basic gears on a Mini are well and evenly spaced and, as 'nick' says, the top gear will always be 1:1.

Just enjoy the retro-driving as it was in the 1960's - that's what classic Mini driving is all about.

[carbon]

If that's a true 70mph then you're final drive is lowish. Might be a 3.44 or 3.65.

 

A 3.44 would give about 4,250 rpm at 70mph

A 3.65 would be about 4,500 rpm at 70mph

[Cooperman]

The 3.44:1 is the ideal FDR for a modified road 1275, unless a really hot cam is fitted when an even lower one may be needed to keep it 'on the cam'.

 

The Mini is not a modern car and it really can't be made to go like one. The pleasure is the retro driving experience.

[Sprocket]

Lets get one thing straight here right away............. Most of the A series five speed gearboxes are an overdrive fifth, fourth is still 1:1.

 

Only the KAD straight cut five speed is 1:1 fifth.

[Spider]

Some of the JKD Gearboxes are also 1:1 in 5th.

[Spider]

There ware around 60 Minis built in the factory, fitted with JKD 5 speed gearboxes, so, depending on your point of view, you could say they were a factory item, albeit, limited run.

 

Sadly that JKD of that era no longer exists.

 

A cheaper option to a 5 speed gearbox would be to fit a final drive ration that will run at around 3800 - 4000 RPM in top gear at your desired cruising speed. Couple that up with standard, or if you can find a good set, twin line gear set and that's a happy medium next to a 5 speed.

 

From my experience, the A Series engine is happy singing along day after day at 4000 RPM. It is fast compared to more modern engines, but I've found no ill-effects from it.

 

However, fitting to tall a final drive - if too tall - will kill these engines in short time from labouring the engine while trying to drive around 'normally'. They also take all the fun out of them.

[Sprocket]

Some of the JKD Gearboxes are also 1:1 in 5th.

the only  tive speed box with 1:1 fith is the KAD, it always has been. it is all to do with how the five gears are fitted in the box. KAD are the only company to have sqeezed in all five gears into the same place all others have four gears. any gearbox that has the additional gears on the other side of the centre web is an overdrive fifth including the JKD.

[mini13]

I'd like to see more info on those JKD boxes as Ive never seen one. I guess its possible if you swap the gearchange pattern about, not sure why it would be of benifit though.

 

there was another 1:1 top 5 speed back in the dim and distant, the collotti, bit to be honest its probably best forgotton!

 

http://mk1-forum.net...61d2fa5fd2ef761

[tiger99]

The economy models, 998 City E and HLE, had higher low down torque than standard and ran a 2.95:1 final drive. They were excellent motorway cruisers, as far as a little car like a Mini can be. That same ratio would be good for a 1275 with a wide power band, but if your engine is highly tuned it is likely that it is somewhat peaky and you would have problems with lack of torque low down.

 

The injection models with mapped ignition etc maintained good low down torque and could run 2.76:1.

 

With a narrow power band you need close ratio gears and because the car needs to be useful over a wide speed range you need more of them. That is why you seem to need at least one extra gear.

 

I think that a 1275 engine with a broader power band and a 2.95 FD would be ideal, but that would usually come at the expense of absolute peak power. Sometimes less is more...

 

Do you have a power and torque curve for your engine?

[Spider]

I'd like to see more info on those JKD boxes as Ive never seen one.

 

The ratios were 1st - 2.567:1,   2nd - 2.1:1,   3rd - 1.579:1,   4th - 1.2:1 and 5th 1:1

 

They were around in the 1990's, maybe earlier.

 

 

 

These were made well before KAD did theirs. KAD started from the JKD 5 speed with 1:1 5th and developed it further.

 

<EDIT: Here's the last page from that 2008 JKD Price List that has a drawing of the Gearset layout used in these JKD 5 Speed Gearboxes with 1:1 5th;-

 

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Edited by Moke Spider, 22 April 2017 - 10:55 PM.