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The speedometer cable is likely bad
87 Monte Carloif 87 Monte Carlo has a cable type release clamp on a small pair of vice grips and pull hard.
connected to the back of the odometer and runs in to the transmission it pulls out
Try on the top of the starter - follow the + battery cable
Generally, yes.
unhook a battery cable for about 3 minutes and re-hook.
Unhook it from the tranny and then the other end is up under the dash hooked to the speedometer, unhook it and take the cable out, just reverse the process for installation.
Remove the positive cable from your 1998 Monte Carlo battery. Remove the cables from the front of the starter. Remove the starter retaining bolts. Reverse the process to install the new starter.
Depending on what you mean by "repair", the common issue for a speedo not working in an 80s Monte, is due to a bad cable, which would just need replacing. Your question needs a little more detail.
Low coolant? Bad thermostat? Heater control cable not adjusted properly? Heater core airbound? Heater core plugged?
Check coolant level? Heater core plugged restricted, or airbound? Defective thermostat? Water pump not circulating coolant? Heater control cable not adjusted properly?
Begin by removing the radio retaining cover. Remove the radio retaining screws. Slide the radio out. Remove the wiring harness and the antenna cable from the back of the radio.