Best Answer dklawson , 02 April 2014 - 08:10 PM
You will still be talking to Speedy Cables or someone.
Most Smiths speedometers from the 1960s and early 1970s had screw-on cables with an M12x1 thread. On the gearbox end of the cable the thread is 3/4"x26. That is generally true of both BMC and Standard/Triumph parts. In the mid- to late-1970s they started introducing the cables that push/clip onto the back of the gauge. The gearbox connection remained threaded on the Mini but the Triumphs went to a flange mount cable... at least for the 4-cylinders.
GT6 production continued until about 1973 so you can put the GT6 speedometer in place and buy a cable of the "right" length as long as it has the M12 thread at the top and 3/4" thread at the bottom. Stags continued until about 1978 so you will need to look at the back of the gauge to see if it has the M12 thread. I suspect if it has the push-on top cable end, the bottom end will be the flange type and that means a custom cable.
With the cable issue is behind you, turn your attention to the gearing. The common GT6 speedometer will be calibrated for 980 turns per mile (TPM). There was another calibration available for cars with a higher final drive ratio but I don't know what its TPM number is. I have no idea what the TPM number is for a Stag. Regardless, it is VERY unlikely that the TPM value will match what is correct for your project. For the speedometer to read correctly the TPM from the gearbox must match the TPM calibration of the gauge.
Yes... you can have the speedo re-calibrated. Speedometer recalibration is not that expensive. Changing the odometer gearing for calibration IS expensive. An alternative is to contact Speedy Cables or similar and have them make you a ratio box. The ratio box mounts inline on the speedometer cable. As its name implies it converts the cable TPM from the gearbox to the correct output TPM to match your speedometer. This was once a common item when people routinely switched the final drive gearing or tire size on their cars. I have no idea who in the U.K. could supply the ratio box but I would start with Speedy Cables. For more information and pictures about ratio boxes see the link below from APT in the U.S.
http://gaugeguys.com/speedcorrect.htm
EDIT: Also, have you considered an analog dial, programmable electronic speedometer? VDO has a number of items available. For the classic Smiths look you might want to visit the Caerbont web site to see what they can offer. To use these you connect a pulse generator either directly to the gearbox or to the end of a short speedo cable. The gauge itself is programmable so you can set it for an infinite number of combinations of final drives and wheel/tire sizes.
Go to the full post
Up Into Fourth
Posted 02 April 2014 - 07:46 PM
I was originally planning to put a Smiths centre dial in front of the driver in the Midas but my attention has been drawn to some Triumph clocks from either a GT6 or Stag. Does anyone know if the centre speedo cable will fit these clocks or whether the Triumph cable will work with the Mini gearbox?
I know I could get a "special" made up by Speedy Cables but I would rather use stock parts as it's less of a hassle!!
Moved Into The Garage
Posted 02 April 2014 - 08:10 PM Best Answer
You will still be talking to Speedy Cables or someone.
Most Smiths speedometers from the 1960s and early 1970s had screw-on cables with an M12x1 thread. On the gearbox end of the cable the thread is 3/4"x26. That is generally true of both BMC and Standard/Triumph parts. In the mid- to late-1970s they started introducing the cables that push/clip onto the back of the gauge. The gearbox connection remained threaded on the Mini but the Triumphs went to a flange mount cable... at least for the 4-cylinders.
GT6 production continued until about 1973 so you can put the GT6 speedometer in place and buy a cable of the "right" length as long as it has the M12 thread at the top and 3/4" thread at the bottom. Stags continued until about 1978 so you will need to look at the back of the gauge to see if it has the M12 thread. I suspect if it has the push-on top cable end, the bottom end will be the flange type and that means a custom cable.
With the cable issue is behind you, turn your attention to the gearing. The common GT6 speedometer will be calibrated for 980 turns per mile (TPM). There was another calibration available for cars with a higher final drive ratio but I don't know what its TPM number is. I have no idea what the TPM number is for a Stag. Regardless, it is VERY unlikely that the TPM value will match what is correct for your project. For the speedometer to read correctly the TPM from the gearbox must match the TPM calibration of the gauge.
Yes... you can have the speedo re-calibrated. Speedometer recalibration is not that expensive. Changing the odometer gearing for calibration IS expensive. An alternative is to contact Speedy Cables or similar and have them make you a ratio box. The ratio box mounts inline on the speedometer cable. As its name implies it converts the cable TPM from the gearbox to the correct output TPM to match your speedometer. This was once a common item when people routinely switched the final drive gearing or tire size on their cars. I have no idea who in the U.K. could supply the ratio box but I would start with Speedy Cables. For more information and pictures about ratio boxes see the link below from APT in the U.S.
http://gaugeguys.com/speedcorrect.htm
EDIT: Also, have you considered an analog dial, programmable electronic speedometer? VDO has a number of items available. For the classic Smiths look you might want to visit the Caerbont web site to see what they can offer. To use these you connect a pulse generator either directly to the gearbox or to the end of a short speedo cable. The gauge itself is programmable so you can set it for an infinite number of combinations of final drives and wheel/tire sizes.
Edited by dklawson, 02 April 2014 - 08:14 PM.
Up Into Fourth
Posted 02 April 2014 - 09:40 PM
Best. Answer. Ever.
Thank you 
0 members, 0 guests, 0 anonymous users
