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+--- Thread: Early Speedometer 4 Speed Gearbox (/showthread.php?tid=1828)
Early Speedometer 4 Speed Gearbox - Mark McKibbin - 03-10-2018
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?
RE: Early Speedometer 4 Speed Gearbox - Chris KC - 03-10-2018
See recent thread 'Speedo Gearing' Mark.
Boils down to an adaptor box or recalibrate speedo I think.
Or fit teeny wheels....
RE: Early Speedometer 4 Speed Gearbox - Steve Hainsworth - 04-10-2018
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
RE: Early Speedometer 4 Speed Gearbox - Roger - 04-10-2018
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
RE: Early Speedometer 4 Speed Gearbox - Martin Prior - 04-10-2018
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.
RE: Early Speedometer 4 Speed Gearbox - Mark McKibbin - 05-10-2018
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)
RE: Early Speedometer 4 Speed Gearbox - Ruairidh Dunford - 05-10-2018
More info here:
http://pub25.bravenet.com/forum/static/show.php?usernum=2099944454&frmid=5&msgid=936935&cmd=show
RE: Early Speedometer 4 Speed Gearbox - squeak - 05-10-2018
(05-10-2018, 08:13 AM)Mark McKibbin Wrote: 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/