Traveller speedo

[Gwmarina1275]

Hi, I have a 1275 Ital engine coupled to a type 9 gearbox in my Traveller. The Speedo reads about 10mph less than the car actual speed. Does anyone know if the Speedo can be adjusted for this error or any other method for correction. Cheers

[don58van]

The reading of Smiths magnetic speedos and be adjusted to a certain extent by adjusting the strength of the spinning magnets in the mechanism. This is a fairly skilled process and requires some equipment to measure the change of reading while adjusting the strength of the magnets. So a speedo specialist might be your best bet (expensive though). I have adjusted some speedos with my home brew setup but I don't know whether it is possible to squeeze an extra 10mph out of a healthy Minor speedo. It depends on how much magnetic 'headroom' is available to increase the magnetism. This method will fix the speedo reading but will not change the odometer. The odometer can be adjusted by changing gears inside the speedo.
Other possibilities are a different speedo drive cog in the gearbox (I don't know what is available for the Ford gearbox) or a 'correction gearbox' that is inserted into the drive cable to adjust the rotation to precisely your requirements. The latter can be supplied to your requirements by our friend Declan Burns (I don't know how his charges compare with adjustment by speedo specialists).
Don

[svenedin]

Basically there are different model variants of the same basic Smiths speedo that differ in the TPM (turns per mile) number. This is written on the dial of the speedo and what it means is how many turns of the speedo cable =1 mile indicated on the odometer. This is also directly connected to the indicated road speed.

The speedo drive cable comes from the gearbox. The number of rotations of that speedo cable for 1 mile travelled on the road is determined by the circumference of the road wheel and tyre fitted (e.g non-original wheels and tyres will alter the speed reading if the circumference of the tyre is different) the type of gearbox and the ratio of the differential. So it is quite complicated to work out which Smiths speedo model variant would be the correct instrument to give an accurate road speed. To be honest, I don't know how you work out which one you need!

I have only very recently started to use GPS navigation (I know, I'm very late to the party) and I can say that the speedo indicated road speed is very closely aligned to the GPS indicated speed. At around 50 mph the disagreement is 1 or 2 mph. This is probably due to a slight difference between the original tyre circumference and the modern equivalent fitted. My speedo was professionally refurbished and recalibrated a few years ago.

Stephen

[geoberni]

I had to replace Basil's Speedo when I brought him as the odometer had been broken for 7 years according to the MOT record....
I also replaced the speedo cable after that because the needle swing would oscillate between 40-60

The current situation, checked with my Garmin GPS Unit is spot on up to about 45, but then under reads such that at 55 displayed, the GPS reads 63.

I'll live with that.

[Gwmarina1275]

Thanks folks for your replies, rather a complicated matter. I have installed an electronic GPS Speedo / odometer which I've buried in the dashboard hole forward of the steering wheel which I'll probably live with. The original Speedo still looking good despite it's innacuracy. Many thanks.