For reference, 3.44 final drive will result in approx 16 mph per 1000 rpm, 3.1 final drive approx 18 mph per 1000 rpm.  So at 60 mph, on 10" tires, I was spinning the engine at 3750 with 3.44, 3400 with the 3.1.  Not a huge difference but enough that I was glad that I made the change. 

So I looked around.  Found a website that you can plug in the numbers and determine your approximate gear ratios.  When I plug in the speeds and engine rpm's it looks like my final drive is higher than the 3.44 Jeremey was talking about.  Our host shows a 3.10 and 2.76, curious????

That's what I tell to anyone that asks.  Consider where most of driving your mini occurs.  The cylinder head/camshaft combination on my engine produces a lot of torque so the 3.1 final drive is fine around town and on secondary roads, particularly on 10" tires. If you have the occasion to take it on longer trips, you'll be glad you opted for the taller gears.  I've driven my car to several events up and down the west coast, to East meets West events in Winona, MN and Milwaukee, WI.  The only time that I noticed a difference was when climbing long uphill grades, like the Rockies.  To be fair, a couple of friends who have the 5 speed say they have the advantage of closer 1-4 gear ratios and the luxury of a 5th gear 'overdrive'.  But I agree with Jeremy.  

I finally got to talk to Jerremy up here in Oregon.  He suggested changing the final drive to 3.1 from the probably 3.44.  Cheaper than the 5 spd and then with the issue of weakness in some 5 spds, it might be the way to go.

...beat me to it

Interesting observation about 5-speeds (from Suzy) is that they're great in LHD cars but the lever sticks into the back of your leg in 5th in a RHD car.
I still want one though, as the ability to have a nice low FD for acceleration in 1-4 and a sensible overdrive for cruising in 5th is appealing.

From what I recall, Trannex WAS mini Spares - KD set it up as a sideline or similar.

Mini Spares did take over Tran-X (for sure their 5 speed Mini business.) They might also be the source of their in-house gear sets.

Not sure when JKD reputation went down,  I would guess in the 1990s.  I knew of them in the 50s making Formula Junior gears, in the 60s and 70s they had good stuff for Minis and Imps and little competition except maybe Colotti.  I got my JKD 5-speed in Canada on a road trip in 1972.  Got a deal because reverse was damaged, so I used that as my class project in vocational school machine shop.  The teacher took an interest, after I made the new gear he took it to where he worked and they hardened it.

//mk1-performance-conversions.co.uk/pdf/motor-11267-5speed.pdf

//mk1-forum.net/viewtopic.php?f=31&t=28481&p=243720&hilit=Jack+Knight#p243720

What happened to Trannex, did they get absorbed by Mini Spares?

Spank, I'm not sure what is to come. I realize I no longer want to support the overhead required to be able to do it all. I'd like to just do engine and tranny maybe sub frames complete. I'm wrapping up a couple now and would like to move to much smaller shop and complete my projects and call it done. Be safe and know there are still people here who care about each other. Steve

Interesting, Steve. If I'm reading between the lines, as is the case with most of your posts, you have a service to sell, eh?

I love doing trannys, I have been rebuilding them since I was 11 years old. Went into my first mini gear box at 18. Shortly after retiring in 2000 I noticed there were JKD 5 speeds on E bay. I bought two of them complete in the box. It seems they were selling for $1500 and I figured I could afford that. After a good hard look and the issues we had with JKD dog box parts I decided to put them on the shelf. In time I was offered $4500 for one and later $5000 for the other. Needless to say I no longer have a 5 speed. I play with the possible gears offered as factory. I have four wide ratio 4 speed with 2.76 CWP and 2 over drive drop gears. Smoke the tires in first gear if that's your thing and cruise 70 mph at 3000 RPM. Mine has recorded 96 mph and the one under the Swift Road Rocket and recorded speeds above 100. I have a customer waiting for a single gear to repair his $5000 5 speed ( not one I sold ) and no luck so far. Steve (CTR)

Well I'm going to keep looking.  The one's our host has listed are near $5000.  Close to what I paid for the TREMEC for my corvette.  My car has a great 4 spd and in the local roads around me the speed limit of 55 is not an issue.  Now if I need to go into the city via the freeway I get 62mph and 3900rpm.  That's why a 5 spd overdrive would be nice.

Compared to a A+ box the spread is even.

A+ - 1st gear 3.640 2nd 2.180 3rd 1.420 4th 1.00 
5spd 1st gear 3.282 2nd 1.966 3rd 1.283 4th 1.00 5th .882 (.865 straight-cut version)

The 5 speed is roughly similar to the "S" and 1275GT boxes 1-4.

So an A+ with 2.76 FD - 1st gear 3.64 x 2.76 = 10.0464, 2nd gear 2.180 x 2.76 = 6.01, 3rd = 3.92, 4th 2.76

5 speed helical and 2.76 FD - 1st 9.05, 2nd 5.42, 3rd 3.54 4th 2.76 5th 2.43  This would IMHO be sluggish and the super-tall 5th of little value.

5 speed helical and 3.44 - 1st 11.29, 2nd 6.76, 3rd 4.4, 4th 3.44, 5th 3.03  This gives a good boost in all the lower gears, but 5th is just a bit lower than I'd like. I've been wondering whether the difference between 2.76 and 3.03 is really much on an issue, but if I recall correctly it's about 300 rpm @65 mph. Maybe I wouldn't notice, but I'd like to be closer to 2.76.

5 speed helical and 3.1 FD - 10.17, 6.09, 3.98, 3.1, 2.74 - practically identical to the A+ box, so what I'm getting for nearly 5 grand is a more even spread of gearing. For me, not worth the expense since I'm not racing.

For me, a "street" 5 speed with A+ gears and the overdrive .882 would be ideal. It would give a nice acceleration boost in the lower gears over stock, and still match the 2.76 in 5th (using a 3.2 final drive.) Either that, or a .80 5th gear, but I'm not sure that's possible.

I understand these boxes are basically made to order (our host might have them in stock since these come from the UK) so I've often thought maybe they could be custom ordered with the A+ gears, but no luck so far... perhaps our host could do it?

Yes, they are essentially 4 speed boxes with the special shafts and the added 5th gear on the other side of the box. 
parts are available, much too complicated to sell on the website, we typically reserve them for customer builds.

I had a jack knight 5spd, helical, at one time. My wife lost a bet (we would frequently bet that she would win an engagement ring and I would win a 5-speed gearbox) and to her credit, she made good by paying for it. When I sold it years later (still unused, NOS in original box) she required I give her the $ back...

She still doesn't have an engagement ring.

Anyway, One thing I discovered after owning that JKD 5-spd was that, because of it's design, it could only run a 3.44 final drive and the over drive 5th was not much different from just installing a 3.1 (again, loosely throwing out ratio numbers here). I didn't think that it was worth it when I could just put in a 3.1 without any real acceleration penalty and save thousands of $.

Personally, I'd rather have at least a 2.9 or better still a 2.76 overdrive 5th with a 3.44 type 1st-4th ratios.

Minispares (and presumably the Minimania boxes) are (or WERE back in the day when they were advertised but "unavailable/out of stock" for what seemed like eons) took a standard 4spd gearbox and added a 5th gear, essentially a conversion box. They USED to advertise being able to just buy the overdrive conversion bits, but again, they were never in stock, seemingly. I wonder if this could be the way to put in, say, a 3.1 final drive and end up with 2.76 overdrive...

A little more research.  MM does have 5 spd gear boxes.  One thing I'm still looking into.  The TREMEC 5spd I put into my 65 Corvette is perfect.  Four speeds, close ratio and evenly spaced with the overdrive 5th at 1:068. 

The one's on MM are not evenly spaced especially 3rd-4th.  If you shift at 5000rpm there's about 20mph in each gear until you shift into 4th where it only drops about 10mph.  Here are the numbers using TREMEC's calculator.  Based on shifting at 5000rpm, 3.44 final ratio, and 20" tires (13" wheels).  1st-25mph, 2nd-44mph, 3rd-67mph, 4th-78mph and 5th-98mph.

Shifting at 5000rpm only 10mph difference, well shifting at 3000rpm, 3rd and 4th would nearly feel the same.

I'll do some more research.

I support the 2.76 final drive option to get drivability 

On first reading of that... I thought "It ain't gonna fit!"

You are wasting your money or want to have bragging rights. A 5 speed still has the 1 to 1 ratio.

Our site search is funky - it doesn't like the term "5 speed"

but we do list them:

Helical Gear 5-Speed
Helical Close Ratio + X-pin Diff
Straight Cut Close Ratio + X-pin

I thought about a Mini 5 speed for a long time. My opinion is that these are great if you're a performance oriented driver (i.e. semi or full competition) who wants to keep the Mini cooking within a specific powerband. The spacing between gear ratios on the 5 speed boxes (if our host's box is the same series of boxes I'm thinking of, which I'm certain they are) is very even, no big drops or rises, and a bit of overdrive for some cruising headroom.

But if one is looking for a cruising box, where you throw it into overdrive 5th for (relatively) quiet highway motoring, the drop isn't enough IMHO. If you pair it with a 3.44 or higher final drive, there's not much improvement if any over a 3.2/A+ 4 speed combo and none over a 2.76 FD. If you pair it with a 3.2 or 2.76, then there isn't the same urgency from 1st and 2nd because the 5 speed 1st and 2nd are taller (lower numerically) than the A+ box.

The ideal (for me) would be the A+ 1st - 3rd gears and a 3.2 final drive, or a taller 5th paired with a 3.44. With a torquey MPi injection motor, the big drop in the A+ gearing isn't that big a deal performance wise, especially on the street, and it will pull the tall final drive well on the highway.

(one thing I forgot - the straight cut box has a taller 5th than the helical box, so if the noise of the straight cut is acceptable, then that just might work for me. But I can't decide or know if the noise of the straight cut is too much for my ears.)