Is there a standard speedo worm & pinion combo for Metro Turbo boxes?
Turbo Mini Forums

I'm just trying to work out my speedo calibration, and didn't remember to count the worm teeth when I had the 'box apart. (Bollocks, as you say in the UK?). I do know that I replaced the 18t pinion that was fitted with a TXD1006 (also 18t) pinion.

Any ideas how many teeth the worm is, or is likely to be?

Are there only certain worms that will drive an 18t pinion?

The car runs 165/60R12, 3.21 diff, and I've got a new 1280 rev speedo. I'm hoping that it won't need calibration....at least close enough to get me through inspection, then I can just make use of a GPS.

Thanks in advance for any help.

Great job on the forum too everybody - there's a lot of people helping a lot of people here. Great to see.

Matt

As you realise, it depends on the speedo as well as wheels/tyres, and the Metros had different TPM speedos to Minis (much lower from memory).

Every Metro box I have stripped has always had a 5 tooth worm whereas Minis alway have 6 or 7 teeth because of the speedo difference.

I don't think there is any pinion that will give you what you want if your box has the 5 tooth worm.

There are a couple of very good calculators on the Net, I'll see if I can find the links.

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

Thanks Rod, that's very helpful. Some links posted on this forum have led me to a couple of good calculators, which are helpful, but none allowed me to guess what the pinion was. Now the question is, can I change the pinion with the gearbox in the car? It certainly looks possible, but it'd be good to hear from someone who knows!

It isn't the pinion that you need to change particularly, it's the worm/pinion combination, and if you have the five tooth worm, it's the worm especially that you need to change.

To change the worm, you need to get the plastic "pinion" out first.... That is like undoing the speedo cable at the bottom end but even harder........ but it can be done, so if it was only the plastic gear...... difficult but not too bad.

But if it's the worm that needs changing, after removing the plastic pinion, then you need to get the two small bolts out and the small plate off the end of engine mounting alloy cover.....

except that there is an alloy adapter bolted on top of this (3 studs through the gearbox and one strange countersunk phillips headed bolt)....

and on top of this is the bracket that does the engine mount and bottom of the radiator, and on top of this is the radiator and engine mounting block.....

So if you can remove the radiator, the engine mount, the steel bracket, the alloy block, the two small bolts, and get some pliers in there to pull the worm out....... all without removing the engine, well done !!!

Sorry to sound cynical - I'm sure it's possible given enough time (the phillips headed bolt will be VERY difficult in situ) - but I personally would take the engine back out.

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

this may help,


Speedo drive spindle and pinion data –
Tooth count Tooth count
Final Drive Ratio Pinion Colour Part no. Spindle Colour Part no.
All pre-1980 17 white 22A1881 6 none 2A3720
3.44 16 green DAM2905 6 none 2A3720
3.2 18 red TXD1006 5 red TXF1004
3.1 16 green DAM2905 7 blue DAM6028
2.76 15 black TXD10004 7 yellow TXF10001


also this calculator is very good,

http://www.guess-works.com/Gearbox/Technical/ratio.htm

this may help,


Speedo drive spindle and pinion data –
Tooth count Tooth count
Final Drive Ratio Pinion Colour Part no. Spindle Colour Part no.
All pre-1980 17 white 22A1881 6 none 2A3720
3.44 16 green DAM2905 6 none 2A3720
3.2 18 red TXD1006 5 red TXF1004
3.1 16 green DAM2905 7 blue DAM6028
2.76 15 black TXD10004 7 yellow TXF10001


also this calculator is very good,

http://www.guess-works.com/Gearbox/Technical/ratio.htm

this may help,


Speedo drive spindle and pinion data –

Final Drive Ratio Pinion Colour Part no. Spindle Colour Part no.
All pre-1980 17 white 22A1881 6 none 2A3720
3.44 16 green DAM2905 6 none 2A3720
3.2 18 red TXD1006 5 red TXF1004
3.1 16 green DAM2905 7 blue DAM6028
2.76 15 black TXD10004 7 yellow TXF10001


also this calculator is very good,

http://www.guess-works.com/Gearbox/Technical/ratio.htm

bugger, dunno what i did there!

Edited by Joe C on 22nd Feb, 2009.

Heres another link I found useful-

http://www.tomsminisite.co.uk/speedo_calculator.php

Rod,
You make a valid point. It's a big ask, to change the worm and pinion in situ. I'll have a think about it before I tackle it. If I pull it off, I'll let you know. If not, you'll hear nothing from me! The alternative is to just get the speedo calibrated. But according to one online calculator, it would be 30% out. Not sure if you can calibrate a speedo to that extreme....
Cheers
MAtt

Matt,

It is very likely to be a 5 tooth worm if the box came from a Metro and has never had the worm swapped to better suit a Mini, but you could (with a little ingenuity) confirm it without dismantling anything down there......

Disconnect the speedo cable and push a cardboard disk over the square end of the inner cable with a large mark so you can count it revolving.

Jack up one side front wheel and mark it too.

With box in neutral rotate the wheel say 20 or 30 times (the more the better) and count how many revs of the speedo cable occured.

Look up (or measure) the rolling circumference of your tyre and do some basic maths to convert the number of revolutions you did to a fraction of a mile ..... Don't forget to divide that by 2 as the action of the differential (with the other wheel on the ground) will cause the cable to do half the TPM it would normally. Divide the number of times your cable revolved by that fraction of a mile and you have the TPM.

As you know you have an 18 tooth plastic wheel, the accuracy of your wheel/disk counting only has to be reasonably close to differentiate between a 5 or 6 or 7 tooth worm using the calculators mentioned.

Rod.

EDIT - got my multiply and divide the wrong way round, corrected....

Edited by Rod S on 23rd Feb, 2009.

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

Thanks Rod. I'll measure as you suggest. Another look at the gearbox in the car confirms that I'd be silly to try removing the worm in situ. Shame they make it so hard, but I guess that's just typical of these cars we love...
EDIT. Had another think and decided to tackle it. Within 20 minutes, both the worm and pinion are ready to pull out! Mind you, nothing is rusted, stripped, grimey or nasty - as the car is getting a full restoration.... So things are looking up!

Edited by mpe on 24th Feb, 2009.

Me again. I've now got the worm out - it's 5 tooth. But I can't seem to get the pinion out, and am now wondering if it does actually come out without removing the whole gearbox end cover - or will it pull out with pliers & persistence? THanks.

Hmmm,

Normally you pull the plastic one out first !!!

Once you take out the single bolt holding the metal fork, the alloy tear shaped bit just lifts off but what you have underneath is not just the plastic gear and it's steel shaft, but also a large steel bearing bush that the shaft runs in.

This has to come out with the plastic wheel/shaft, BUT, often is tight in the surrounding alloy. So when you pull on the shaft with pliers, it should come too, BUT, if it doesn't, there are two slots in it - these engage on the previous bit and are meant to stop it turning - so put the previous bit back on withOUT its bolt and rotate it a bit each way to free up the steel bush.

Once free'd up it should come out with the plastic gear.

Rod.

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