Speedo swap

[ericwork]

On one of my cars the speedo has just started jumping and sticking. I have checked the cable which is fine. Now I do have a spare speedo but, and this is the question, it is from a van. Am I right in assuming that this will read wrong if I fit it to the car due to a van having a lower rear axle ratio? The plan will be to use this until I fix or replace the original. I know I can get them recalibrated, but I will be keeping this van speedo standard as it is due to be fitted into my sons van, which I will be starting to reassemble in the summer, (if the sun ever comes out). As a Suplimentary question, I have an early midget gearbox, which I was just going to swap the remote for the morris one, so that I have a reverse switch built in. But the van 'box was a bit noisy. If I change this box over will that not alter the speedo as well, midgets having 13" wheels?

[Onne]

As long as the diameter of the complete wheel is the same, which would mean you have to get tyres with higher walls( I don't know if this is the right term though)

[ericwork]

thank you for that Onne, I have done my sums now and worked out that all other things being equal the change from midget rolling radius to Morris rolling radius results in about a 6% decrease in indicated speed. I will be going faster than the speedo reads. Talking of speedo's did you have a problem with yours, there is one on eBay which is marked in kilometers, could be of some interest to you, only a £5 I think.

[Onne]

Thank you for that, I hope to have my speedo delivered today, a miles one though, I want to keep my car as original as possible