The 1988 700 is the only year they used a 96 tooth tone ring for ABS and the speedo. Prior to 1988 they used an 8 tooth tone ring and from 1989 and on they use a 48 tooth tone ring. Your speedo is reading exactly 1/2 speed because there are exactly 1/2 the number of teeth on the tone ring.

ABS cars use a pulse converter to change the signal for the speedo to use. To repair the unit you could either use the signal converter from a newer car, although I don't know if the speedo is the same or different. Most shops that calibrate speedometers could install an after-market converter, or you could change the signal source for your speedometer to one of the front wheel ABS sensors.

Hope this helps
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Volvord 784VC www.telusplanet.net/public/gilesij/Volvord