Do you mean the speedometer or the odometer ..or both.  In reality they are two different instruments; the odo is gear driven while the speedo has a magnetic drive.  The odo can only be adjusted by changing gears - which you can do by replacing the stock drive or using an intermediate gearbox.  The speedo only needs a change to the distance between the drive and driven plates.

The "cheapest and easiest" way to adjust the speedo only requires a GPS/Smartphone app and a felt tipped pen.... 

Cheers, Ian

Thanks a million Doug. Great info as always. I will call them up and look into these two options. Thanks again. Really appreciate your help.

1) Remove the speedo cable at the speedometer end and measure the square up top.  I think it is .104" but you should measure to be sure.  Don't take my word on it... but I am fairly certain all the others are too big.

2) No, 7/8-18 will not be correct for the Mini.  For the threaded Mini speedometer cables the gearbox end is 3/4-26 and the speedometer end is threaded M12x1.

3) The following information applies to all your questions.  Call the ratio converter company and tell them what car you are dealing with and mention the thread sizes I listed.  They are very likely to say they have nothing for you.  Ask them about an inline ratio box and making custom cables from a NEW Mini speedometer cable.  If the shop knows what they are doing they should be able to take your new speedo cable and cut it in half.  They will put a new 7/8-18 connector on each side of the cut so you now have two cables.  The first cable will go from the Mini gearbox to the ratio box.  The second cable will go from the ratio box to the speedometer. 

Work with the shop.  For them to make the custom cables for you they will need to know where to make the cut.  You need to determine where you want to mount the ratio box to determine how long each cable should be.  I have no great suggestions for you.  Ideally you will be able to make some form of bracket to mount the box on the back side of the engine.

Since this thread was started years ago, you can get GPS speedometers (not Mini specific in design) from Speedhut.  Caerbont (in the U.K) is the current Smiths license holder.  Recently they introduced an electronic speedometer with an analog needle for use with the Mini.  It would work with the pulse generator Air2Air posted the picture of.  

You can read more about the Caerbont Mini speedometer (and see pictures) in the thread linked below.
www.mk1-forum.net/viewtopic.php?f=5&t=14082

Thanks Todd! that's a really nice reference. I will save it for the future. That option will be a major commitment that requires replacing the speedo.  For now i just want my cooper S speedo to read correctly in the most simplest way possible. 

Link I'm losing the cable. I expect abuse here for flashing this:  Classic British Mini Speedometer Drive adapter



Either I do this or a GPS retrofit in the Smiths housing.

Hello gurus, I'm trying to order a ratio adapter for my Smiths gauge from mrspeedometer.com (AKA Record Technologies) and I'm running into a few questions.

1. They have the option of choosing different pin connection size. Which one of these is the square cable connection size is right for our speedo cable?  their options are .104Sq , .150Sq , .156 Dia , .187 Dia , .203 Dia (i'm not sure which one of the squares)

2. Also, these adapter connections are 7/8 - 18 thread. is that the same as our speedometer cable?

3. Lastly, these liner ratio adapters, do i need to connect them at the Tranny end of the cable? or can i sandwich it between the Smiths speedo and the cable?


Thank you for reading. any input is greatly appreciated.

- Link

If you use the www.mrspeedometer.com gear ratio guide the percentage you get from your GPS run will allow you to determine the ratio you need. If you need to go up by 30% then you want 1.7693. In an 800 series adapter that is:(A-gear 12, B-gear 18A, C-gear 15A,D-gear 13A).

The last time I needed a ratio converter was 20+ years ago.  Like you I did not want to send the speedometer out for calibration at the same time. 

What I did was drive a known distance via measured highway mile markers (no GPS back then) and compared the highway distance to the trip odometer reading.  I provided those measurements to the speedometer company (Nichols Speedometer in Greensboro, NC) and asked for a ratio box to suite.  They did object when I did not want to send the speedometer in but they agreed to make the ratio box based on my numbers as long as I agreed to accept it "as is".  The unit worked perfectly for years it was in the car.  I only removed it when I changed the differential.

In short, don't be put-off by the methods they ask you to determine the ratio you need.  Make a phone call explaining what you would like to do and I am sure they will agree to work with you.

 

What neither site makes clear is how they are calculating their "ratio" for their adapters. Based on the information Dan gave me, his transmission drive is producing 914 turns per mile (tpm). His speedometer is marked as being a 1280 tpm calibration.

If the ratio is "In from Trans" : "Out to Speedometer", then he would need a 0.7140625 ratio adapter. If calculated the other way, it would need to be a 1.4.004 ratio adapter.

Edit: The trick will be getting the correct threading for the Mini transmission/cable and the drive key size. The threading is an "odd size" compared with those used by most US cars and at least two sizes of drive key (the size/shape of the cable ends) were used on the various Mini transmissions.

I do appreciate the time and effort for your replies.  Unfortunately I don't feel they will help me.  This is 2013 and from what I see, the first one (counting cable turns over a set distance while pushing the car) will tell me only what the transmission gearing is and would be good to adjust the speedo gearing) requiring me to send in the speedo which I don't want to do.  I don't understand why shops/someone hasn't modernized.  With the advent of GPS and my ability to read the speedometer while driving versus what my actual speed is (GPS) establishes a "percentage" variance between what I read and my actual speed.  Soooooooo why can't a shop make up a gear set to adjust the output of the transmission (in my case add 30% to the output revolutions) to what is needed?  Will it be dead set accurate? probably not, but if I'm within a couple of percent I'd be happy.  At present when my speedo reads 45 I'm doing 60 and the local traffic police don't really believe me (nor care for that matter) :-). 

In regards to driving a measured 10 miles, if I lived in a somewhat open area I could possibly do that but living in the L.A. metro area where it's built up for 60-80 miles in all directions makes it difficult.

 

I had a local guy make up the initial adapter box (but he is no longer in business) so I just had the Gauge Guys supply me with internal shafts and gears so that I could adjust for my new final drive.. I went from 3.44:1 to 3.1:1. They did a great job! www.mrspeedometer.com has a comprehensive gear ratio guide on their website..... using their gear selection guide my GPS calibration allowed me to choose exactly which four gears I needed to get from 0.7784 to 0.7222. [I have a '71 Innocenti so I needed kilometers/hr!]

Visit APT (gaugeguys.com).  They can make the ratio box you need.  It will require you to supply them with some distance measurements.  I suspect you will also have to provide them some indication of where along the cable to put the ratio box. 

//www.gaugeguys.com/speedcorrect.htm

Anyone know of a "speedometer ratio adapter" made for the classic mini?  Ebay lists some for American cars but they have a different thread per inch and diameter for the cable so they won't work on the classic.  I know the "proper" way is to have the speedo ratio changed at a shop but I don't want to take my speedo out for 2 months and lose my fuel gauge and other instruments.  I have two classic's.  One is 30 percent low, the other is 10 percent high.  A site recommended by MPlay lists the various combinations of transmissions and speedometers and tires that will cause it to read high or low.  www.tomsminisite.co.uk .  I'd think there would be a decent market for these adapter as they are common for U.S. truck/cars when you change transmissions/differentials etc that affect your speedometer readings.  Most classic owners have changed either their transmission or purchased a new speedo that doesn't have the proper tpm.