Any gearbox experts?
Turbo Mini Forums

Hi all

I want to try and find out the exact ratios of my gearbox before fitting it. I have taken photos and measurements so hopefully someone maybe able to help:

Idler Gear
1 – 37 teeth


First Motion Shaft Gear (Input Gear)
1 – 29 teeth


1st Motion Shaft, 3rd Motion Shaft
1 – 19 teeth (4th Gear)
2 – 30 teeth (4th Gear)
Synchroniser 3rd/4th Speed
3 – 30 teeth (3rd Gear)
4 – 22 teeth (3rd Gear)
5 – 25 teeth (2nd Gear)
6 – 30 teeth (2nd Gear)
7 – 33 teeth (Synchroniser 1st/2nd Speed)
8 – 30 teeth (1st Gear)
9 – 29 teeth (1st Gear)


Final Drive Pinion
1 – 14 teeth


Differential
1 – 55 teeth (Final Drive Crown Wheel)


4 Synchro Straight Cut Gears – Layshaft
1 – 25 teeth
2 – 23 teeth
3 – 19 teeth
4 – 15 teeth


I have found this posting on TMF but cannot say for certainty which gears are which (http://www.theminiforum.co.uk/forums/index.php?showtopic=3851&hl=). Aslo, Guessworks have a ratio calculator on thier website but once again, not sure what bits are which (http://www.guess-works.com/Tech/ratio.htm).

Finally, I bought this second hand and decided to strip it down before fitting to make sure that it's all ok. I noticed this morning that the 6 bolts holding the crown wheel to the diff were all finger tight. After taking them out, this is what the bolts look like:

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

ring MED and give em the number they'll be able to tell you exactly what it is.

If something is worth doing, it's worth doing half of.

To work out the ratios, divide the big number for each gear by the little number. Then use guesswork's site to work out what set you probably have.

Looks like the crown wheel has been wobling about and has worn out the bolts..

How many teeth on your primary gear?

1st - 2.543859649

2nd - 1.731301939

3rd - 1.258581236

4th - 1.0

FD - 3.93:1

Bolts are beyond use.

Edited by Paul S on 19th Jun, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I gave MED a shout and all they could tell me was that it is a "S/C C/R WITH QUAIFE ATB AND S/C CWP".

I tried using Guessworks calculator but do not know how to work out the Drop Gear Ratio or the Worm & Pinion Ratio.

The primary gear is a standard Metro Turbo one (haven't got it here so cannot tell).

With those figures, am I able to find out what I could get out of each gear in MPH with certain tyre sizes on them?

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

That isn't a Quaife ATB - well it's absolutely nothing like my one anyway.....

From those slots in the casing it looks like a friction plate type LSD, not an ATB.

Which could mean parts have been swapped since MED built it which could explain why the bolts weren't fitted right and are now scrap.

Schrödinger's cat - so which one am I ???

Drop gears will be 1:1 then.

Use guessworks calculator and select Abingdon ST ratios.

http://www.guess-works.com/Tech/ratio.htm

The gears are these:
http://www.minispares.com/Product.aspx?ty=...id=38071&title=

Edited by Paul S on 19th Jun, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thanks everyone.

I see what you mean about the friction plate LSD. Which is better?

I have not built the engine fully yet so have no idea what sort of RPM I would get out of it. It's a standard Metro Turbo with Kent 266 cam and megajolt as the most noteable changes to the standard engine.

What do you reckon the top RPM would be (roughly).

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

You may want to consider changing the FD ratio to something more suitable for a turbo engine. A 3.2 or 3.1 would be much better for road use.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I was just thinking about that. If I change the pinion, the results will be:

14 tooth - 3.929
15 tooth - 3.667
16 tooth - 3.438
17 tooth - 3.235
18 tooth - 3.056

And with the setup I want (Tyres - 175/50 x 13, Drop Gear Ratio - 1:1, Gearbox Type – Abingdon ST), Guessworks says I can get the following MPH at 6,000 rpm.

3.105:1 – 114 mph
3.211:1 – 111 mph
3.444:1 – 103 mph

If I went for an 18 tooth pinion, would that be better or would it upsets things too much?

I live in Jersey so I won’t be going on motorways but would like a decent top speed so that I am not forever changing gears. On the other hand I don’t want it to be bogging down in the gears and feeling too slow.

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

You cannot just change the pinion. The crown wheel and pinion come as a matched pair.

Edited by Paul S on 19th Jun, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Guttered!

MED's lowest one is a 3.47.
MiniSpares lowest one is a 3.4
MiniSport's lowest one is a 3.44

Starting to think about selling the box and reconditioning my standard Metro Turbo box but looking at the prices of S/C gears, diff, crown and pinion but that comes to around £600.00!

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

why not just change the diff??? and keep the box.

one day boost will be mine!

What, change it for another LSD at £500 or for a cheaper X-Pin?

But I would still need to buy a new crownwheel and pinion to get the ratio down to 3.2 (or am I being stupid)?

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

yeah change to a cross pin and pick up a 2nd hand c+p that'll keep the cost down thats what i thought you meant when you said about rebuilding the other box at a cost of £600. or yeah fork out for another lsd with the available c+p.

one day boost will be mine!

For the road, use the Minispares cross pin diff. You should be able to pick up a crown wheel and pinion for around £40. The only thing you'll need then is the diff output shafts, maybe diff output side covers depending on which ones are fitted for the LSD.

should be no more than £250 depending on how many of the 'other' bits i mentioned you need to find. If you already have a standard box, you'll already have the output shafts and the side covers, maybe even a 3.1:1 crown wheel and pinion

You can get any crown wheel you like and have it machined to go onto an LSD, think the price I was given was about £100.

The £600.00 was for a SC gear set from MiniSpares at a cost of £353.07, a MiniSpares Molybdenum Cross Pin Diff at a cost of £136.16 and a crownwheel and pinion 3.1 ratio at a cost of £120.00:

(http://www.minispares.com/Product.aspx?ty=pb&pid=38071&title=)
(http://www.minispares.com/Product.aspx?ty=pb&pid=35941&title=)
(http://www.minispares.com/Product.aspx?ty=pb&pid=41995&title=)

The way I see it, I have two options:

Option 1 – Sell the MED gearbox and look at upgrading the standard Metro Turbo gearbox. This would mean upgrading the diff. The cross-pin diff that MiniSpares do, is no longer available (according to their website) so was thinking about going for the MiniSport 4 pin diff at £112.00. Can you use the standard crownwheel and pinion or do I need to upgrade that? Also, is there any point dropping in SC gears or SC primary/input gears if the max I want to go is 150bhp?

Option 2 – Keep the MED gearbox but look at changing the crownwheel and pinion to a 3.4 final drive and then possibly upgrade the primary/input gears to achieve a higher top speed.

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

Why are you selling the straight cut gear set?

What is your real goal here cos I just don't get it. Do you want a staright cut gearbox? cos you already have one. Do you want a limited slip diff or cross pin diff? The crownwheel and pinion will depend on the diff type. anything ess than 3.4:1 and an LSD will require a standard diff type crownwheel to be modified.

What is it that you really want to achieve?

Oh and the 'no longer available bit' means that Minispares are out of stock, not that they will never be doing them again. You could try Minits or dare I say, Guessworks for the exact same diff.

My thinking is that I want to keep costs down but still have a functional car. At the moment, I have spent money on the gearbox and only found out this afternoon that it is not suitable for the car. I bought the gearbox on a whim as a mate of mine needed the cash.

I am not fussed with a straight cut gearbox and just want a functional car. If I could sell the gearbox I bought, and use that money to build a functional gearbox that will take the power I want and have the final drive I want and still have money left over, I would be happy.

I believe that I would get more for a complete box rather than half the box.

Do that sound sensible or am I going about this all the wrong way?

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

Just change the diff, the crownwheel and pinion. The diff output shafts, you should be able to pick up real easy as will be the diff side covers if you actually need them. THAT is going to be the cheapest option.

Then sell the LSD, you will likely get back any money you outlaid.

I don't know whay you were thinking about buying a new gears set when you already have one that will do

So are the diff output shafts and side covers almost unique to the diff i.e. some diffs have to have special covers and shafts?

I have the side covers and shafts for the Quaife diff so if I buy a new diff and fit it and the covers and shafts don't match, I am best off selling them with the diff?

Here's a picture of the diff:

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

Oh, I was thinking about selling the gearbox in the same condition as I bought it rather than swapping out diffs and selling them etc.

Speed doesn't kill, suddenly becoming stationary, now that's what'll get ya!

Those are standard pot joint diff side covers and will be ok. The output shafts for the LSD are specific items for the LSD. You will need standard type pot joint diff output shafts a cross pin diff and a standard crownwheel and pinion of the ratio you want. I woud suggest that for the roard around Jersey the 3.4:1 ratio will be plenty good enough, since the 40mph limit is a bit of a show stopper.