speedo problems...

Hi All

I should perhaps have left this alone.

Sometime ago the odemeter stopped working. Got to 9999 and stopped just as 10000 was appearing. Speedo OK. The speedo is a replacement for the original Smiths one which broke. I had tried to repair this by dismantling. Not having a manual this got a bit difficult (well, it sort of exploded).

The replacement unit was BRITPART (I know, I know what you are all gonna say). When I ordered the new speedo from Paddocks they sent me a Britparts unit. Anyway, this unit broke, I took this apart for a look and could not see anything wrong and now speedo reads high.

Any ideas? Else I am looking for a new speedo (again) and would really like a Smiths.

yer must have the wrong speedo if its reading high, although i think there places that can recalibrate them

It was reading OK. I had to take the pointer off to remove the facia to look inside it. Now I put it all back together it read wrong. Suspect pointer is in wrong position.

Perhaps the question should be - How do you calibrate the speedo?

with a gps satnav system

Drive fast toward a plod with a speed gun, he'll kindly tell yer what speed yer was doing

I knew I could rely on you all.

Ok, so I make a rig to load speedo into the lathe. I know, i think, the various gear ratios from wheel to speedo. What do I assume is the mean diameter of the wheel? I as going to measure the effective radius from the ground to the wheel centre.

this might save yer some bovver

Today I adjusted the speedo and then tested it by driving it with a variable speed electric drill set to rotate anti-clockwise.

By using the stopwatch on my mobile phone I was able to measure time taken to 'cover' set distance. It's reading a bit high:

Run 1; Distance=1mile, time=67.29 secs, indicated speed=54mph, calculated speed=53.8mph

Run 2; Distance=1mile, time=32.24 secs, indicated speed=32mph, calculated speed=30.95mph

I think its OK

steamcoaster said:

Run 1; Distance=1mile, time=67.29 secs, indicated speed=54mph, calculated speed=53.8mph

Run 2; Distance=1mile, time=32.24 secs, indicated speed=32mph, calculated speed=30.95mph

Click to expand...

don't think you'll get much more accurate than that!! mine's ~5mph high and doesnt get over 55, either that or everyone up here drives really slowly all the time!!!!

Top tip seems to be to fit needle pointing straight down. Once fitted, the needle can then be wound forwards to rest on the stop so pre-loading the spring the correct amount. They must install the needles like that in the factory.