Early Speedometer 4 Speed Gearbox

[Mark McKibbin]

I have at last finished the special and on the first drive noticed the speedo reading about a third what it should do (odometer as well). I'm pretty sure if it was a magnetic type speedo it could be adjusted to suit but not sure about the "PA" mechanical type. Not fussed about the odometer.  I know there are ratio adaptors available that attach to the cable but is there another way?

[Chris KC]

See recent thread 'Speedo Gearing' Mark.

Boils down to an adaptor box or recalibrate speedo I think.

Or fit teeny wheels....

[Steve Hainsworth]

If you  replace the worm wheel and pinion with same  from a 3 speed the speedo will read right.
It means stripping the output spider and removing the rear cover from  both boxes . there will be a small amount of  machining to the bronze worm to fit it to the 4 speed box.
Just make it measure the same as the 4 speed one. the worm has more starts on it which gears up the speed about 2 x.
Cheers Steve H

[Roger]

Mark,
When my speedometer was not working I found the gearbox was assembled with no worm drive fitted.
This would obviously have caused problems as it acts as a spacer on the gearbox shaft.
On investigation I found there there were variations on how many starts there were on the worm and also how many teeth on the pinion. I had an 8 & 9 tooth pinion available so fitted the 9 tooth pinion and single start worm.
They appeared compatible but The Speedo shows about 30mph, the satnav reads 40mph.
There is an article in the BA7C somewhere I believe about speedometer drive gearing.

Roger

[Martin Prior]

My RP has got faster and faster over the last couple of years and now regularly clocks 75mph!

Meanwhile, the 5-mile run into Hereford has stretched to around 300,000.

...........and as I'm now getting around 15 million mpg, why should I complain? Maybe that explain why the fuel gauge never moves.

[Mark McKibbin]

Thanks for the replies, I think I will make a ratio correction box that will, as the speedo goes to 100 mph, make it read kph as I live in the metric country (Australia)

[Ruairidh Dunford]

More info here:

http://pub25.bravenet.com/forum/static/s...5&cmd=show

[squeak]

Thanks for the replies, I think I will make a ratio correction box that will, as the speedo goes to 100 mph, make it read kph as I live in the metric country (Australia)

Mark I have used these guys in Brisbane. They do a cable inline gearbox, quite robust and any ratio you wish. They do a lot of classic cars and bikes. cheers  Russell

 http://www.ottoinstruments.com.au/