The sender wheel, inside the diff, must be replaced if your car has got the 12 "teeth" non ABS style. 1989 and newer ABS cars used 48 teeth wheels. Earlier ABS cars used 96 teeth wheels and different sensors. Avoid these parts if possible, they're more expensive and sometimes difficult to locate. I'd also guess the 96 teeth front wheel senders are more prone to failure. Also note that 96 teeth senders won't work with 48 teeth wheels...btdt.

If your car has got a 12 teeth setup, the diff cover also has got to be replaced. This is an easy way of recognizing the different setups - 12 teeth covers are sheet metal where 96/48 teeth are cast alloy. Volvo btw switched to 48 teeth wheels for all models, ABS and non-ABS, at some point in the early nineties.

You'll also need a frequency divider to convert the signal back to 12 pulses/axle turn for the speedo. Pick the divider out of a 200/700 series ABS car (700 series with the old style dashboard).

Martin
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'65 121, '73 165