Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing speedometer 4/4 1978

just wondering if one of you kind folks could id the smiths speedo on a similar model and read the quite small numbers on bottom of the face ,if your eyes are like mine youll need some magnification, mine reads made in uk snt (or it could be 5) 5372/00 1000 which i think is possibly the gear ratio ,i have a speedo which is currently reading 10mph slow according to gps but is smooth in its travel and as the car has had some odd mile readings over its life there is some possibility that its been changed ongoing thanks for all your good help, one of these days i'll have to figure out how to get a pix into my profile

Hi Bruce
I have a 1977 +8 with what I believe a similar speedo to yours. I am in Tauranga so will check when I go to the garage to see what is written on mine.
Will be in touch
Regards
Doug

On my '71 4/4 the numbers are either side of the centre point of the Smiths speedometer needle and read SN-63 920.

My 1980 model has the same numbers as yours.

Hi Bruce
The +8 speedo reads Made in UK SNT 5372/03 1000.
This probably not much help.
Regards
Doug

cheers thanks for the feedback looks like another job for winter i'll need to factor in the difference or the boys in blue will be paying me some attention i'm also going to paint on some red markers as the km/h are a little small for my eyes now lol

An old style mechanical speedo is a 2 part instrument, an odometer and the speedometer. The odometer is purely mechanical with a constant ratio between the input cable and the mileage drums. The input cable also spins a magnetic drum which then magnetically pulls a flywheel which has the speedo needle afixed to it around.
You can play around with the odometer part by swapping the end gearwheel and pawl for gearwheels with a different number of teeth - but - not a lot of point really. The distance between one town stays the same whatever the instrument reads.
The magnetically driven drum isn't capable of re or de-magnetising to reset the speedos calibration.
You can however reset the instrument for the most critical speed for yourself.
Drive the car against your gps at that specific speed and note the instrument reading.
Remove the speedo cable and then the instrument from the car. Ease the peened over bezel mounting tags, twist the bezel and remove. Release the mounting screws on the back of the instrument to allow the removal of the complete innards. Use a finger to rotate the needle to the indicated speed that you know the true speed of and hold it there. Mark a pencil line on the flywheel against a fixed part of the cage behind the dial. Release the needle and then prize the needle off, using a pair of tea spoons as levers. Rotate the flywheel to your register point and then re-affix the needle showing the correct gps speed.
Thus the instrument is recalibrated, albeit to be 100% accurate at only one speed, but you know which one, and which other speeds either side are safe or licence endangering. Sounds crude but it works and give reasonable level of comfort.
Reassembly is in the reverse order.
Smiths, in their own service literature, recommend cleaning and re-greasing (not oiling) the cable every 10,000 miles, probably worth pulling the cable inner out and doing that whilst you're poking around under the dash.

thanks for that in my basic understanding i thought i might advance just the needle 10 so that i would be doing 10 at rest but i will take your info onboard as you have given good advice thanks bruce

My speedo, 1971 4/4, is only accurate when the car is stopped.

Any other time the needle oscillates around the speed you are doing, I have changed the speedo cable, made sure it is routed with only smooth bends all to no avail.

Maybe oil or grease has got into the head.