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Posted: Wed Sep 10, 2003 5:05 pm
by Cam
The gearbox speedo drive is more than likely the incorrect ratio for your speedo.
You can rectify this by getting your speedo re-calibrated by Speedy Cables. I don't know how much it will cost for the early speedo, but it's about £40 for a late type.
Posted: Wed Sep 10, 2003 5:16 pm
by Cam
To be honest, I have never stripped one down (except to change the mileage readings.........cough
), so I'm not sure. why not take it apart and have a look? it can't be that difficult unless different parts are needed.
Posted: Wed Sep 10, 2003 7:11 pm
by Kevin
This is also a sign of general wear my 65 speedo has a 20 - 30 mph variable swing at all speeds once under way and the later ones are prone to this with mileage/old age if yours is a constant error why not follow a car with a good speedo make a note of where it is at certain speeds and put stickers on the speedo this will get you out of a spot for the moment
Posted: Wed Sep 10, 2003 8:21 pm
by lowedb
I had a similar problem on my '53 (although not twice the speed). The needle is held onto the shaft by friction, and it had slipped. By taking the thing out of the Can and holding the bit that drives the needle, it was easy to turn the needle relative to the drive. The car was running correct (but not original) gearbox and the original axle. This will only work if the speedo is the problem and you are putting it back to what it should be.
It's still possible the gearbox is wrong, too.
The relative position of the needle / disc / and the return spring, combined with the strength of the spring determine the calibration of the needle, but don't affect the odometer. That's just a function of the gear in the gearbox, and the gearing inside the speedo unit. It's not just a case of tweaking one part, either.
To be sure what your problem is, try checking it at several speeds. Is it a constant 10 / 20 MPH out, or a constant percentage out. The first suggests a slipped needle, the second a ratio problem. Also check the odo accuracy. If this is wrong, again a ration problem. Try a GPS unit to check things, and remember car speedos have to read between -0%, and +10%+4kph so most read around +2%.
Posted: Wed Sep 10, 2003 8:48 pm
by turbominor
Speedo's are adjusted by changing the level of magnatisation of the main disk at the back of the speedo using a special tool. Have seen them altered before, and it can only be done with the correct stuff
If you have a 1000 box in an early Series II it will read about double!