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Smiths Racing/Caerbont Speedo Calibration
Sanzomat - 14/3/22 at 08:56 PM

Hi All, any experts on these speedo's out there in internet land?

I guess it must be a good sign that everything else is working when I work my way down the list to the speedo not working!

When I bought the car the speedo signal input was connected to the Yamaha R1 (4xv) speed sensor on the engine/gearbox casing but the speedometer wasn't working. There was also an inductive sensor on a bracket facing the propshaft bolts but whilst the wires for this was routed to behind the dash they weren't connected.

I've now disconnected the yamaha sensor and connected up the inductive sensor. There are two different signal input wires on the speedo, one for ECU type signals and one for inductive. The previous input was connected to the ECU one. I've connected the inductive signal wire to the inductive input.

Now, instead of nothing at all it seems from my video of Keevil that the speedo is now doing something but at 100mph (from the gopro gps) the speedo is creeping up to a dizzying 10mph. I'm guessing this just means it needs calibrating to the pulse count from the sensor.

The instructions I've found cearbont instructions suggest I should be able to enter the calibration mode by holding the trip reset button whilst powering it up via the ignition key. This isn't working though. All I seem to be able to do is reset the trip back to zero or toggle between odo and trip displays. I've checked that the supply is switched on the key and it is so not sure what else to try to get it into calibration mode. Anyone else had this problem and found a solution???

SteveWalker - 15/3/22 at 12:31 AM

How old is the speedo? Older ones did not have a calibration mode. Instead, they had a removable rubber bung on the back of the speedo and under that was a row of DIP-switches. Calibration consisted of calculating the pulses per mile, looking that up in the instructions and setting the appropriate switches to match. If it is that type, unfortunately I can't help, as my instructions were nibbled to bits by a snail!

falcor75 - 15/3/22 at 05:17 AM

using some google fu I managed to find this, maybe it helps.

https://www.caigauge.com/documents//product-instructions/spedometers/speedometers/speedo-dip-switch-tables-437.pdf

JMW - 15/3/22 at 01:45 PM

quote:
Originally posted by Sanzomat
Hi All, any experts on these speedo's out there in internet land?

I guess it must be a good sign that everything else is working when I work my way down the list to the speedo not working!

When I bought the car the speedo signal input was connected to the Yamaha R1 (4xv) speed sensor on the engine/gearbox casing but the speedometer wasn't working. There was also an inductive sensor on a bracket facing the propshaft bolts but whilst the wires for this was routed to behind the dash they weren't connected.

I've now disconnected the yamaha sensor and connected up the inductive sensor. There are two different signal input wires on the speedo, one for ECU type signals and one for inductive. The previous input was connected to the ECU one. I've connected the inductive signal wire to the inductive input.

Now, instead of nothing at all it seems from my video of Keevil that the speedo is now doing something but at 100mph (from the gopro gps) the speedo is creeping up to a dizzying 10mph. I'm guessing this just means it needs calibrating to the pulse count from the sensor.

The instructions I've found cearbont instructions suggest I should be able to enter the calibration mode by holding the trip reset button whilst powering it up via the ignition key. This isn't working though. All I seem to be able to do is reset the trip back to zero or toggle between odo and trip displays. I've checked that the supply is switched on the key and it is so not sure what else to try to get it into calibration mode. Anyone else had this problem and found a solution???


Pretty sure I had the same problem when recalibrating my Racetech Programmable Speedometer when I changed the trigger wheel. I just kept persevering, getting only the options you described, until one time it did what it was supposed to do. I wasn't aware of doing anything differentl that final time, maybe some time interval was different, but whatever, it finally worked. Good luck!

Sanzomat - 19/3/22 at 05:24 PM

quote:
Originally posted by SteveWalker
How old is the speedo? Older ones did not have a calibration mode. Instead, they had a removable rubber bung on the back of the speedo and under that was a row of DIP-switches. Calibration consisted of calculating the pulses per mile, looking that up in the instructions and setting the appropriate switches to match. If it is that type, unfortunately I can't help, as my instructions were nibbled to bits by a snail!


Thanks, perfect advice. I've just had a look at the back and there is indeed a rubber bung beneath which is a row of dip switches. That will explain why the trip reset button isn't putting it into calibration mode.

Sanzomat - 19/3/22 at 05:29 PM

quote:
Originally posted by falcor75
using some google fu I managed to find this, maybe it helps.

https://www.caigauge.com/documents//product-instructions/spedometers/speedometers/speedo-dip-switch-tables-437.pdf


Those tables are just what I need. Looking at the current dip settings the table suggests my pulse count is currently set around a factor of 7 away from what it needs to be based on calculating the wheel size, diff ratio and bolt numbers. Taking a still from my video of Keevil the speedo was reading 14mph when the Gopro GPS data says I was doing 92mph - factor of 6.6. Seems like you guys have cracked it for me. I'm very grateful.

SteveWalker - 20/3/22 at 01:23 AM

Glad to hear that the problem was simple in the end. It was only because mine was installed 22-1/2 years ago that I have experience of the older type and remembered setting it up (using a pocket computer, running a basic program, while the car was on the rollers for SVA, to calculate the difference and tell me which choice from the table to change the settings to.)