Speedo sender unit interchangability

[John Robertson]

HI ALL how does the Speedo work by impulse or mechanical means .Can you alter the reading of the cars speed by replacing a sedans Speedo module on the differential with one from a wagon .Or are they the same ?
I have a 740 turbo with 205 -55-16 tyres or tires and would like to go to 225-60- 16 a more common size here and cheaper .My Wife has 195-60-15 on her 740 turbo could we go 205-60-15 a much cheaper tyre tire to buy , using the sender unit on the back axle .We love our Volvos so we got our son a 1990 240 to learn on and boy its fun to drive ,with 195-70--14 tyres .
Same question again is 205 or 215 -60-14 a reasonable conversion using the rear diff sender .Thanks from down under where the water flows the other way or does it ?

 

[James Sweet]

HI ALL how does the Speedo work by impulse or mechanical means .Can you

alter the reading of the cars speed by replacing a sedans >Speedo module on
the differential with one from a wagon .Or are they the same ?

I have a 740 turbo with 205 -55-16 tyres or tires and would like to go to

225-60- 16 a more common size here and cheaper .My Wife has >195-60-15 on
her 740 turbo could we go 205-60-15 a much cheaper tyre tire to buy , using
the sender unit on the back axle .We love our >Volvos so we got our son a
1990 240 to learn on and boy its fun to drive ,with 195-70--14 tyres .

Same question again is 205 or 215 -60-14 a reasonable conversion using the

rear diff sender .Thanks from down under where the water >flows the other
way or does it ?


All 700 series cars use an electronic speedo with a sensor in the rear axel
unit. The sensor is the same, but the calibration of the speedometer varies
with tire size. 240's used a mechanical cable speedo until '85, after that
they got the same electronic setup as the 700's.

 

[John Robertson]

thanks.. so that means that the speedo can be adjusted by the sensor type ?

 

[Michael Pardee]

thanks.. so that means that the speedo can be adjusted by the sensor type
?

I wouldn't think so. Typically reluctor sensors are just a winding on a
magnetized core, and they count the number of teeth that go by. A new sensor
could change the output level but can't change the rate.

Mike

 

[James Sweet]

thanks.. so that means that the speedo can be adjusted by the sensor type

?


No, the calibration is in the speedo itself, I haven't looked into the
details though, it might have a potentiometer you can adjust, or it might
use soldered or plugged jumpers, you'd have to check.