GPS Speedo?

[nigelv8]

Hi

Have seen that the VOSA have changed the rules for the MOT and vehicles now have to have a working speedo. Problem is that mine hasn't worked for the last 4 years

Have changed the speedo cable from the T5 box but this didn't fix it. Have looked to replace the speedo drive to find that the cog it meshes with in the box is missing. This would presumably be fixed if I got the box rebuilt.

Now I've seen that you can get speedos that measure the speed by using GPS. Has anyone got any experience of these and if they are any good.

I can see one possible problem in that when the cars being MOT'd it won't be moving when the tester looks at the speedo when the car is on the brake rollers.

Any thoughts on this?

[richardpope50]

Many speedos take pulses from a set of magnets around the prop shaft but there are other ways being from an ABS sensor pickup, drive shaft bolts or make your own as I did (OK for Dax Rush).

Speedy Cables is the place to go for anything like this. They converted a TVR speedo into one that was adjustable by me for my made-up metal drive shaft disc (with fingers).

Someone recently failed an IVA because he used the front wheel ABS sensor and his rear wheels drove the test equipment. Not quite MOT but similar problem.

[katanaman]

GPS speedo will fail because it isnt a road legal certified speedo. For example they wont work very well in areas with tall buildings and wont work at all in tunnels. Better to do as above and get either your drive replaced which wont be expensive or replace the whole lot with one that counts pulses say from the propshaft.

[nigelv8]

Thanks for that. I was thinking that there might be problems with the reception in built up areas or where there was poor coverage.