Speedo Reading Low

[Robbie 2B]

Finally got the car back on the road with the Duratec HE just about fettled. One of the problems still to overcome is that the speedo is indicating a little on the low side.

 

As I have used the Mondeo instrument cluster the speedo requires a signal from a vehicle speed sensor (VSS). I have used a sensor from a Ford Ka and fitted this to the Type 9 gearbox using an adapter. The signal from the sensor goes via the ECU to the speedo. The system works fine but an indicated 15 mph is way over 30 mph.

 

Looking at pass posts there was a discussion that a 'sequencer' was available which can alter the speed sensor's output.

 

Can any guidance be given on

 

i/ Do different mechanically driven VSS give different signal outputs?

ii/ Are 'sequencers' available and if they are where from?

 

Any help gratefully received.

 

Best regards

 

Robbie

[sj-bradley]

Is this a pulse driven speedo?

 

It might be possible to design a divide by two pulse counter or some other electronics that would do the job.

What you are looking for is some sort of frequency converter - yes?

 

You could also make a new chopper wheel for the sensor. (Is it designed that way? It might be possible to remove some of the lugs which would make it seem slower to the sensor)

 

Simon.

[Robbie 2B]

Simon

 

Thanks for the reply.

 

The original Mondeo VSS is a pulse type, a serrated disc on the drive shaft activates a sensor, which is magnetised, fitted through the differential casing.

 

The one fitted is from a Ford Ka which is a rotating magnet driven by the Type 9 gearbox speedo drive, photos attached.

 

The possibility of fitting an ABS sensor to the rear wheels is the next option to explore if a sensor driven from the gearbox is not possible. Where any Sierra's fitted with rear drums and ABS? Any other options to explore?

 

Robbie

[sj-bradley]

It sounds like the drive from the gearbox is not spinning the magnet fast enough so you are only getting half the pulses required for the correct reading.

 

I misread your first post thinking the speedo was too high. I think you might be able to add another magnet opposite the one on the sensor and this will give you twice the rate and about what the speedo needs.

 

You could also try and source or make a gearbox to increase the speed of the sensor.

 

Or you can do similar with a frequency doubler to double the amount of pulses to the speedo.

 

Something like this

 

http://www.eleccircu...bler-with-4069/ (Link doesn't work any more, try next one)

 

http://www.eeweb.com/blog/circuit_projects/cmos-4069-driven-frequency-doubler

 

Although there are probably simpler circuits to try out.

 

Simon.

[sj-bradley]

I've just been surfing the web to see if there is anything simpler, but not really.

 

It sounds like you need another magnet on the driven shaft to give you twice as many pulses to the speedo.

 

Sorry I can't help more than that though.

 

Simon.

[fry61]

Smaller road wheels???

[sj-bradley]

There is another simpler circuit here

 

http://datasheetoo.com/diode/full-wave-frequency-doublers-using-diode-and-transformer-circuit-diagram.html

 

but the output is probably not the same shape as the input.

 

Simon.

[Longboarder]

I would have thought that using a sensor for the same car as the ecu/instrument cluster came from would be the simplest solution.

 

Nigel

[Robbie 2B]

Thanks for the posts.

 

Concur with the thinking about using the original sensor. The problem is with how will the sensor picking up or generate a suitable signal? Mk3 Mondeo's use the transverse 75 gearbox with the sensor pick up wheel located on the differential output shaft. A Type 9 gearbox does not have this ability nor a location for the sensor.

 

The option of fixing a suitable crenelated wheel to a drive shaft and fixing the sensor to the differential chassis housing would appear to be the best mechanical option. My knowledge of electronics is based around twin valve super-het transmitters so unless I can get a plug and play unit this method is not an option.

 

Thanks again for your time and efforts.

 

Robbie