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need advice: adapting '94 940 speedo to an '87 740 700

posted by  M on  Thu Jan 17 01:22 CST 2002
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last visit: Sat May 1 10:12 CST 2010
[RELATED]

This issue is kind of special because of your early ABS eqiuppped car. The 87 should have a 96 teeth sender wheel in the differential. This was replaced by a 48 teeth wheel on 1989- ABS models. All 900 cars used the 48 teeth sender. BUT non-ABS 700 cars (until 1990) had a 12 teeth wheel, which is what the 700 speedometer requires. That's why the signal passes through a part of the ABS system on your car - this simply is a divider which gives the speedometer its required 12 pulse/axle turn signal from the 96 pulse input.

As you might already have figured, the 940 speedo uses the 48 pulse/axle turn signal as is (so does the 940 ABS system). This is why it reads a quarter of the correct speed (12/48=0.25) or double (96/48=2) speed depending on the way you connect it.

This also gives a not-so-simple solution to the problem, since you can't tap a correct, 48p signal for the 940 speedo anywhere. Solve the problem with a separate divide-by-two cirquit and use the original speedo signal (not the ABS system output).

/Martin
--
65 121, 73 165






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