Speedo worm drives

[Keith Halstead]

3-rail box (mk1 Cortina + mk2 Cortina series 1):

22 teeth, natural/clear, 105E-17322-B
23 teeth, black, 107E-17322, FINIS 1713654
24 teeth, green, 109E-17322-B
25 teeth, blue, 109E-17322-A

single rail box (mk2 Cortina series 2):

22 teeth, natural/clear, 3050E-17322-A, FINIS 1430670
23 teeth, black, 3024E-17322-A, FINIS either 1419570 or 1546880?
24 teeth, green, 3038E-17322-A, FINIS 1426309
25 teeth, blue, 3024E-17322-B, FINIS 1419571

 

[Brian c]

Does anybody Know what drive is needed for 2000E box to 3.9 diff as per standard mk1 Lotus ?
Great post Keith.

 

[puntasanjacinto]

Indeed great post.

And how would one determine correct worm drive with standard gearbox (1966 Mk1 export LC) however a changed rear end to 3.7 Salisbury? Thank you.

 

[ray8829]

Brian, I seem to remember using a Black/23 teeth drive in my rally GT with 2000E/3.9 diff/175x70x13 tyres. I required an accurate speedo for the regularity sections and Halda device.

 

[Keith Halstead]

Great post Keith.

Thanks Brian - I did lift the info from elsewhere on the forum & I'm trying to centralise all the stuff that keeps getting requested on the forum & our facebook page to make it easier to find.

 

[Keith Halstead]

Indeed great post.

And how would one determine correct worm drive with standard gearbox (1966 Mk1 export LC) however a changed rear end to 3.7 Salisbury? Thank you.

I think Speedy Cables do a calibration guide which shows these variables.

 

[Brian c]

Brian, I seem to remember using a Black/23 teeth drive in my rally GT with 2000E/3.9 diff/175x70x13 tyres. I required an accurate speedo for the regularity sections and Halda device.

Perfect Ray , thanks.

 

[Pete G]

So how do you select which one you should have?
Is it according to the diff ratio, in which case what speedo dive goes with which diff ?

 

[ray8829]

Its a combination of diff. ratio and wheel/tyre circumference, I am sure there must be a table out there somewhere. Alternatively you could use a good GPS to give you an accurate speed of your car and check against the speedo reading. Work out the % error in your readings, see what drive gear you have in the box and then work out which one that will give the same speedo and GPS readings.

 

[Keith Halstead]

Its a combination of diff. ratio and wheel/tyre circumference, I am sure there must be a table out there somewhere. Alternatively you could use a good GPS to give you an accurate speed of your car and check against the speedo reading. Work out the % error in your readings, see what drive gear you have in the box and then work out which one that will give the same speedo and GPS readings.

Speedy cables have a sheet they give you to calculate it.

 

[scrab]

This post is titled "worm gears" but correct me if I wrong it's the wheel gears that are being discussed.
My question is are there different worm gears? as well as different wheel gears?

 

[Keith Halstead]

This post is titled "worm gears" but correct me if I wrong it's the wheel gears that are being discussed.
My question is are there different worm gears? as well as different wheel gears?

Which bit is the worm gear & which the wheel gear?

 

[scrab]

The worm is the blue gear, the wheel the green.
I assume the previous discussion has been about the green type of gear.
I took my wheel gear out this morning and it has 24 teeth. Replacing it with a 25 tooth gear is not going to correct my speedo enough to make it read correctly, so I was wondering if there are different worm gears with different numbers of teeth. (not that I can see myself rushing to dismantle the gearbox again, but it would good to know.

 

[Pete G]

I gave up on this!
I use the rev counter to know my speed @ 17.5 mph/1000 rpm for a 3.9 dif.
So if there is a speed camera, keep it below 2000 (in top) in a 30 limit and about 3000 in a 50 limit

 

[Brian c]

It does list the combinations in the parts manual, unfortunately not the lotus model. Iisted as driving gear and driven gear. So 2 types of driving gear(part inside gearbox) listed.

 

[scrab]

It does list the combinations in the parts manual, unfortunately not the lotus model. Iisted as driving gear and driven gear. So 2 types of driving gear(part inside gearbox) listed.
IMG_20210228_095349.jpg

Thanks for that. I'd been looking for it in the parts book and couldn't find it, I assumed it was in the gearbox section. I didn't count the teeth on my worm gear when I took the gear out yesterday, but today I looked at a spare gearbox I have and that has 6 teeth. So if mine on the car has 7 at least I've got one to swap it with if, I decide to strip the box.