Technical speedo problem

[Rickythebricky]

hi , recently bought a "B" in England & have taken it back with me to France
the speedo dial reads KMPh but the car is to be set up for MPH & registers on the dial as mph ? is there a box of tricks somewhere that would revert the speedo to reading KMs
cheers in advance for any help

 

[s130]

Well this could be done but it is not that easy.

The speedo is driven from the final gearbox/differential drive to the drive shaft.

To my knowledge the speed sender is common to both UK / EU cars and the pulses per km or equivalent mpg are the same. So x pulses are turned into a voltage that gives an analog needle deflection of y degrees. So y is constant for any given speed be that meters per second, feet per second, km/h or mph. The y deflection is then read against two legends where eg. at 100km/h the needle is at the same y deflection as 62 mph.

I think what you want is the your more prominent MPH scale to effectively display km/h?

This means that you need to reduce the y deflection by a factor of 62/100=0.62

However now you km/h scale is really screwed. This could be a French vehicle safety test failure.

You best options are:

1) get the dial legend replaced with a EU one or put a EU speedometer in
2) put a larger / clearer km overlay on the speedo glass

3) have an additional display driven form the ODB data or ABS sensors

I imported many years ago a Fiat 600D from Belgium where I used to live to the UK (1970s). The speed was only in km/h so I used red dymo tape to make 10mph, 20mph ..... 60mph labelled markers and cut thin strips for line markers. These days one can print/make far better professional overlays.

 

[Rickythebricky]

many thanks s130
the dial seems to be the original one , although it has a piece of coloured card over the right hand side of the dial that covers all from 140 & over , the card has MPH on it , & the speeds are in MPH when i'm driving as is the odometer, so as you say the correction from KM's to MPH was done via the speed sender
once again thankyou

 

[s130]

Looking on ePER the gearbox sender unit is the same for LHD and RHD drive cars.

However the speedo head unit (all guages/dials) are different with listings for EU, GB/Ireland and Japan.

This all means that it is the dial back plate legend that is changed for km/h and mph and not the sender unit or the head electronics.

 

[Rickythebricky]

s130
it would seem mine is different , the dial is definitely the original with kms marked on it but the speedo needle registers in MPH on same dial , as i said before the dial has been half covered up to 140 but when peeled back it shows a dial up to 240, so from this i can only conclude that it was modified on import to Britain in 1998,
cheers again for the input , owning this car is one hell of a learning curve

 

[s130]

What someone has done then is a relatively simple hack.

The speedo is in effect a simple analogue meter. If it read 0-100km and say 1mph is 2kmph then you use a simple 50/50 divider and blank off over 50mph. In your case the reduction ratio is 0.62. So 162km/h = 100.

What does the odometer read. Is that now showing miles or km?

 

[Rickythebricky]

What someone has done then is a relatively simple hack.

The speedo is in effect a simple analogue meter. If it read 0-100km and say 1mph is 2kmph then you use a simple 50/50 divider and blank off over 50mph. In your case the reduction ratio is 0.62. So 162km/h = 100.

What does the odometer read. Is that now showing miles or km?

the odometer reads in miles , everything is in mph , when doing 50mph it reads 50 on the dial except i know the dial is a KM dial

 

[s130]

I give up

 

[StevePD]

Hi all, I have done both sides of the continent with the Barchetta. The hardware is the same, simply need to change the graphics for the speed needle indicator. You can do this on the front surface of the dials crudley by putting markers at the equivalent speeds such as 80 Km/50mph, or go the full hog and mark or replace the graphics behind the speedo needle in the instrument panel itself. I think this is what has been said previously but my discription if it helps.
Steve
D