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Easy. The early racks have an aluminum housing where the pinion shaft is. On the later rack this housing material is steel. Steve Golik Smoky Mountain Z Car Club Knoxville TN 1970 240Z 1974 260Z 1979 810 Hardtop "30 years of Z car ownership"

I have an early tach schematic I will post after I get it scanned. It’s just a very basic two transistor astable (one-shot) multivibrator circuit that drives the meter coil. The transistors are type 2SB189 (PNP 25V 250mA). Looks like you can still get them: http://www.ceitron.com/semi/ceitoshiba.html Steve Golik Smoky Mountain Z Car Club Knoxville TN 1970 240Z 1974 260Z 1979 810 Hardtop "30 years of Z car ownership"