Speedometer, odometer do not work?

Yes it can. Were you the one with the inoperable speedometer? I've found the best way to check the speedometer is to undo the bolt that holds it to the tranny, pull it out and give it a whirl with your fingers while having someone watch the instrument speedometer gauge. If it doesn't move than you know either the cable is bad/broken, it's not connected very well to the instrument cluster or the (rare) speedo gauge isn't functioning like it should.

If this isn't your problem, just reply and let me know. I thought there was someone here who posted a problem like this, but I didn't get a chance to reply and I forgot who it was.

The speedometer head is the last thing to suspect. The exception would be if the odometer still works.

First suspect the cable. They can snap or the square end at the transmission can round off inside the gear. You may be able to reach behind the instrument cluster to disconnect the cable, then watch or feel if it turns when you move the truck. It's often easier to disconnect the cable at the transmission, then spin it with your fingers while a helper watches the speedometer. That's also the time to inspect the end to see if it's rounded off.

The gear inside the transmission could be stripped too but that's not as common as a snapped cable. If the odometer does work, that would prove the cable and gears are okay. Usually when the speedometer head fails it gives a lot of warning first. The needle will typically bounce around a lot and the assembly will make noise. On rare occasions the head can lock up and cause the cable to snap, so if you find the cable is badly twisted, check the replacement for free movement with your fingers. A locked-up factory cruise control servo can do that too. They were run by the speedometer cable.

If you're not familiar with what a speedometer cable looks like your best bet is to get a copy of the manufacturer's service manual. There will be line drawings and a description of how to remove the end from the transmission. You might find it on one of the online service manual companies too. My computer won't let me access them. I've never figured out why and I gave up trying a long time ago.

All of the speedometer cables in the '70s and '80s were pretty basic. Most had a metal cap that screwed onto the transmission. Typically you will need a pair of pliers to loosen it, then you just unscrew it and pull the cable off. You'll see the spiral-wound cable inside the casing. Spin that cable with your fingers while a helper watches the speedometer. If the needle flickers, the cable is okay.