My mph speedometer actually shows needle readings in kph values. As an example, when traveling at approximately 60mph the gauge is showing 100mph. When traveling around 30 mph, the speedometer needle reads 50 mph. My ‘67 S1 4.2 2+2 was originally delivered to Canada. What do I need to do to fix this problem so I will get the proper mph values?
Hi John,
Welcome to the group.
I find that quite strange. We use KPM in our country and I fitted a KM face on my MPH gauge and it works just fine. The needle is still on the same position on the instrument and therefor reads 100 KPH at the same position where 60 MPH used to be. Obviously the mile meter still counts in miles, but that was the best I could do at the time.
Are your mile meter distances correct?
Regards
Chris
Cape Town
Hi John K, If you look carefully at the face of yr current speedo you should find a TPK ( turns km ) number. Convert that to tpm ( turns per mile ) , and now you need speedo with that number on it . This number depends on a variety of characteristics of yr car, including the gearing in yr differential. There are often lots of speedos on E Bay, and you then transfer the face ( chances are that yr speedo internals are in good or better shape than the one from Ebay!! ). If you find that prospect somewhat daunting , then you will have to send it to one of the speedo specialists who will be able to fix it for you, at a “cost”
Perhaps a photo of the face of your speedo would help.
I would consider that only as a last resort and then only after getting good references. Some shops are not able to correctly adjust a unit for accuracy across the entire range.
My MPH speedo is just as far off. I don’t actually use it though. I generally just motor along with traffic.
I have a Ferrari that is a full 10% off. When it reads 80 it is actually moving along at 72 etc. The problem with that is that the miles rack up just as generous. So now my car shows 10% more miles than actual. In the Ferrari world that hurts as Ferrari Tifosi have some problem with actually using your car and adding miles. I find myself using it 10% less! 
Hi Geo, You could well be correct. I wish to suggest that there is a very helpful document on speedometers :::Repairing Jaeger and Smiths Speedometers by Anthony Rhodes . Anything I might have learned re speedos came from here !!!Once you have become accustomed to the Smiths set up, its quite easy to tke it apart, especially if you just wish to harvest the face!!!
If your car was originally delivered to Canada, it would have had a speedo graduated in miles and MPH. Canada converted to the metric system in 1970.
So you probably have the wrong speedo or one where someone has changed the face, in which case, the serial number on the face won’t help.
The parts list has a listing of all the serial numbers for various countries and diff ratios.
If you post your diff ratio, someone here can tell you what speedo you ought to have.
All this talk about KPH vs MPH may not be appropriate. The way I read the original poster’s symptom was that he has a speedo calibrated in MPH, but it reads high by about the same ratio as KPH/MPH. That is, when travelling at 60mph, the needle points at 100(mph). Maybe, I’m wrong, but that’s what I understood. As others have noted, the needle points at the same angle on the dial whether it is a mph or kph speedo - the scale on the dial is just different. My reading of the original poster’s issue is that the position of the needle is way off for the road speed. Maybe, the original poster can clarify his symptoms?
Is it possible for you to post a picture of the face of your speedometer?
Hi, it may be instructive to determine if the odometers agree with the speed shown on the dial face.
Hugh Pite
Thanks everyone for your response to helping me try to fix my speedo problem.
davidxk, you are reading the problem correctly.
My speedometer is shown in the following attachment:
So with the help of my gps to determine actual road speed in mph, I find that the mph speedo pointer shows a value equivalent to kph instead of mph.
(GPS says 24 mph and speedo pointer shows 40 mph, GPS says 60 mph but speedo pointer shows 100mph, etc, etc)
I think John Holmes may be on the right track (ie. wrong speedometer for the gearing in my differential).
So I guess now my question is how do I find out what diff ratio I have?
It’s a ‘67 S1 4.2 2+2 automatic with all matching numbers.
I do not have a Jag Heritage Cert and the office is currently closed due to Covid-19.
Thanks in advance for your response,
John K.
It’s almost like someone put a ratio converter box in line on the speedometer cable to make a MPH speedometer read in KPH.
Does the odometer read (more or less) correctly? If yes, there is no converter box or diff change, just a need to adjust the needle (fairly easily done, even by the shop with limited understanding).
That is a 1312 TPM unit which is correct for a 3.54 rear end. The simplest way to find out what your diff ratio is is to jack up one rear wheel and turn it to see how many times the propshaft turns for one wheel rotation (though I cannot recall whether a limited slip allows this). You have to adjust your answer since only one wheel is turning (I think you double it but maybe you halve it?). Like I said simple - so simple it makes my head hurt.
Here’s one place where you can find Tony’s excellent monograph:
Current European law requires speedometers to never read low, see section 5.3 of law ECE-R39 at https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A42010X0513(03)
Though not all Euro car owners experience a grossly high speedometer reading, my Ferraris have read pretty high. One was going 14 mph when parked.
Thanks Geo!!! I currently have my car apart so it will be awhile before the car is running again so I can check my odometer. I reset the odometer just to make sure the numbers tumble correctly.
John Walker - I first had that same thought (wasn’t sure if there was such a thing).
I will definitely trace my speedometer cable to see if a ratio converter may have been incorporated. Even though I don’t really know what it would look like, I can still check to see how the cable is attached to the automatic tranny.
I installed one on mine, had a shop splice it into the cable, because I changed rear end ratios. It looks like this (click on the link below or SAM links for pictures).
OK, this is what I have so far…
If the tag on the back of my rear diff cover is correct (shows 43/13), then I have a 3.31:1 diff ratio which means my speedometer is wrong since the face plate shows a TPM 1312 for a 3.54 diff ratio as stated earlier by Geo.
What the spare parts manual shows is C.25186 which is SN 6322/00A (MPH) TPM 1216 due to the 3.31:1 diff ratio.
Now to locate the right speedometer and be that much closer to solving the problem.
Thanks everyone!!!
To be more precise, I need SN 6322/35 TPM 1216 since I am running on 185-15 x 5 wheels. I still will validate the diff ratio matches what the tag on the rear diff cover states and also make sure no one messed with the speedo cable running to the tranny.
Thanks for posting that George. I’ve added it to my reading list as while my speedometer works, my odo never has. So next winter I’ll get it out and sit down to fix it
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Another factor you should consider is that there is more than one ratio to the angle drive on the transmission. I believe that they come in a 1:1 ratio and a 1:1.25 ratio. Search e type speedometer angle drives for more information.