anyone know the speedo drive ratio of a transit MT75?

[Dez]

as it says really. ive got a transit MT75 on the back of a pinto with the adapter plate. would quite like a working speedo, but could do with knowing what the drive ratio is before i buy anything, one so i don't get something that totally unusable, and two so i can calculate what compensator i'll need to take into account my axle ratio and tyre size.

the speedos I'm looking at are all 2:1 ratio, classic bike ones (for appearance reasons).

[bortaf]

TBH without knowing what the origional diff ratio was there's no way to tell without looking SWB diff was differant to LWB and minibus was differant to van.

[colnerov]

Hi, traditionally Ford used to have a speedo number of 1000 and they used to change the speedo driven gear to suit the diff fitted. Do they still do this? Other manufacturers had standard speedo driven gears and changed the speedo number to suit the application. There used to be available cable inline gearboxes to fit calibrate mechanical tachographs. Are these still available or something similar?

Colin

[Dez]

from what i can see i think ford changed the worm drive in the gearbox to change the ratio to suit the axle fitted, as there are 3 or 4 different colours available.

but, i cant find out the actual drive ratio of the speedo unit.

[colnerov]

Hi, that's what I'm saying Fords used to have a standard speedo head ratio of 1000revs/mile but didn't mark the speedo faces because they were all the same. Manufacturers like Land Rover changed the speedo head ratio to for example 1500 for one model and say 1408 for another. I'm not sure I'm explaining this well or am I missing the point.

Colin

[Dez]

Right, I understand you now. We're on the same page I think.

But, how does that equate to a bike speedo described as "2:1 drive ratio"? Tbh I'm not even sure what that means as a quantifiable figure.

Unless its distance to revs, making a ford speedo head about 1.6:1?

[colnerov]

Hi, I suppose it depends where a bike speedo cable is driven from, If it comes straight off the wheel hub the final drive sprocket set won't have any influence on it. If may be similar to an early beetle where the cable goes through the stub axle and is driven by the grease cap then it will be 1:1. I think you need to investigate bike speedo drives.

Colin

[Dez]

They drive off the rear wheel, 2:1 ratio drive unit. At the ages I'm talking about anyways. Seems pretty much all (British) bikes worked like this.

I assume that means 2x cable revs per wheel rev, as the bigger gear is on the wheel axle rather than the cable.

But then you'd need to know your rear wheel rolling radius to calculate rpm/mile.
I don't see any provision for different size tyres there though?

edit, drive unit-
www.ebay.co.uk/itm/NEW-ROYAL-ENFIELD-2-1-STEEL-SPEEDO-HUB-DRIVE-110919-1-/271683702202?pt=LH_DefaultDomain_3&hash=item3f419c4dba

speedo-
www.ebay.co.uk/itm/NEW-SMITHS-SPEEDO-METER-0-80-MPH-BLACK-FACED-BSA-ROYAL-ENFIELD-2-1-5-DIAMETER-/171725506533?pt=UK_Motorcycle_Parts_13&hash=item27fba347e5

I'm looking at these due to size. i need 60-70mm gauge max to fit in my dash panel.

[Dez]

apparently royal enfield 500s use a 3.50x19" rear tyre.
stated diameter for an avon SM mk2 in that size is 682mm. converted to imperial, 26.8"
not deducting anything for rolling radius as opposed to theoretical(which i should really, but i don't know how much), thats a circumfrence of 84.3"
63360 inches in a mile.
63360 divided by 84.3, 751.6 wheel revolutions per mile.
2:1 drive so x2, 1503revs per mile. call it 1500, that sounds very plausable.

still don't answer the original question though
but, assuming fords are deffo 1000rpm/mile, it means the speedo is being underdriven by 33%. or, the gearbox output needs overdriving by 50% if you look at it that way.

none of that takes into account my current axle ratio (which i don't yet know) or tyre size against the original transit one though. i guess thats next on the list....

[colnerov]

Hi, I was going to suggest a Land Rover series 1 speedo as they are about that size but they probably won't be that sort of price. Perhaps most bikes of that era had similar overall size tyres plus I don't think accuracy was that important at the time, I think most speeding convictions were based on the opinion of the officer.

Colin

[colnerov]

Hi, Dez, I suppose a call to speedy cables may get them to confirm or deny.

Colin

[Dez]

yeah, its the only classic looking gauge i can find in that size thats less than a million pounds. and it seems all the aftermarket bike ones are 2:1 as well so i don't have a lot of choice really. i guess as you say most tyre sizes were close enough for any error to not be that great.


i now know what speedo drive cog i have, its a blue 23T one-

so i now need to go do some more googling to see what axle that is for, then drop the diff pan on mine to see what ratio i have.

[Dez]

apparently its for a 4.11 axle. what mk transit is a smiley, mk5?

[frag]

Apr 1, 2015 20:43:58 GMT Dez said:

apparently its for a 4.11 axle. what mk transit is a smiley, mk5?

Yep,
MT75 was fitted to transit from last of mk3's (F reg onwards) there are close and wide ratio's available too....

I have more info and possibly some regarding speedo drives but its at work,i'll have a look tmrw if I remember.

[Dez]

excellent, sure it will be useful to me. it appears all the date stamps on the engine/box are from 1992, so thats what I'm dating it as, although its got a points dizzy in it so i assume thats been changed. i think that actually means its a mk4. off to google again to find the tyres size now...

[frag]

185/ x 14 on smaller models,225/70 x 15 larger vans,from memory.
If its Transit pinto it will be low compression.

Gearbox ratio's for mk4

Close ratio Wide
1st gear 3.89:1 4.17:1
2nd 2.08:1 2.24:1
3rd 1.34:1 1.47:1
4th 1.00:1 1.00:1
5th 0.82:1 0.82:1
rev 3.51:1 3.76:1

Timken rear axle,diff out of front ratios
4.11,4.56,5.13

Salisbury,
4.63,5.14 & 5.83.

[frag]

Dez,according to E-cat,for the '92 transit (though I guess '95 will be same).....

Drive gears are as follows.
21 teeth,4.63
22 teeth,4.63,4.56,5.83,3.90
23 teeth,5.14,4.11
24 teeth,5.13/5.14,5.83
25 teeth,4.63,5.14

The drive scroll in gearbox,
5 teeth,Green,5.83
6 teeth,Yellow,5.13/5.14,4.56,4.63
7 teeth,Natural/Blue,3.91,3.90,4.18,4.11
6 teeth,Blue,4.56

Hopefully this is of some use,
Also,I know your aiming to run cable speedo,but if it helps later transit used these gears in MT75 to drive a 3 wire electronic speed sensor and run speedo head........

[tallmatt]

It's a bit of a bodge, but before now I've used a bicycle speedo on various vespa scooters. you'll have to araldite the magnet to your wheel and the pick up to a strut on a car I guess. Depending which one you use, you then get to program the rolling diameter, the pick up diameter, and it does the rest.