Car in bits again...
AO Silver Member
Join Date: Feb 2007
Location: Hampshire, UK
Hi guys! This little teaser might exercise the grey matter for a while!
I have been re-comissioning a 1982 Rover SD1 trip computer for use in the Green Machine. I have sorted out the wiring, changed the VFD display colour to blue (to match the rest of my instruments), and confirmed that my speedo sender (Dakota Digital ac generator) does in fact drive the unit.
But here's the thing - the computer cannot be electronically re-calibrated for a different speedometer drive gear - only a change in the gear teeth on the sender does that on the original car. My DD speedometer however, can be calibrated, which is what I have done to match it to my 1982 Alfasud gearbox.
So at the moment, if I connect the computer up as it is, my speedo will be accurate, but the computer mpg and trip distance calculations will not. One way I could overcome this is to recalibrate the speed sender to suit the computer and then recalibrate the speedo to that. Or I could simply not bother!
(1) Does anyone know how many teeth the Nylon speedo gear in the gearbox has? I think it is 10... If so,
(2) Does anyone know how many teeth the corresponding driveshaft gear has? I need this information to calculate...
(3) What is the ratio of the two?
(4) Failing any of the above, does anyone know what is the standard Alfasud speedometer calibration? Is it printed on the face of the speedometer dial somewhere? I assume it will be in revolutions/km
I have got the wheel and tyre, final drive ratio and speedometer sender gear ratio data for the SD1, so I am trying to find out just how far apart the speed calibration is between the two applications. That way I will be able to decide whether to use the same sender and live with the corresponding mpg/trip distance errors or have a go a changing the speed sensor pulse train with a prescaler and recalibrating the speedo.
Please help, this is making my brain hurt!!!
Alfanauts are GO!!!