'86 Speedometer/Trip Odometer Question

It's all mechanical gearing behind the speedo head. Most likely it can be repaired, but you will probably need a parts speedo to remove parts from to swap in.

I have a pic of my stock '88 speedo head somewhere showing how the gearing is. It *might* be similar to the '86 speedo just to give you an idea of what sort of work it would be to fix it.

I've taken these speedos apart a few times to match mileage. It's VERY easy to do, but you definitely want a good work area with lots of lighting as it's a bunch of small gears and pins to align properly.