1985 Speedometer?

[1ton]

My wife and I just acquired our 1985 GMC. The speedometer is not working. I have pulled the cable loose from trans and used a drill to turn the cable. the speedometer and the cable are ok. now it has a greenish grey gear on the bracket? that the cable screws into and inside the trans is a purple/red gear. is this the right set of gears. Also its a TH350 Trans. Any help would be appreciated.

 

[MrMarty51]

You might check a parts diagram and, I believe, that there is suppose to be a "White Plastic" cable adapter inside of the square that the speedo cable fits into.
If that adapter is gone, the inner cable will be too small and cause the cable to not spin with the speedometer drive pinion.
Some of those had a steel adapter to make it to a square drive.
Also, is the end of the cable got the corners rounded off ???
OH yeah, welcome into the forum and, be sure to post us in some pics; Most of us like "Square Porn".

 

[1ton]

I did not see any white plastic piece. As far as the cable, it has 2 rounded corners and 2 normal. I put the gear back into the cable after it was out of truck and it seemed to be a good fit on the speedometer cable.

 

[chengny]

Reach up under the dash, release the clip from the back of the speedometer head and draw it down lower so you can work on it.

Hold the sheathing in one hand and push the cable (the steel inner cable) down into the sheathing a bit (2-3 inches if possible). Don't worry you can always get it back.

This will give you some extra cable sticking out of the sheathing at the transmission end. Use that extra length to be sure that the square tang at the end of the cable fits properly and well into the recess in the gear.


Make it back up to the transmission as normal. This should return most of the cable (the 2-3 inches that you pushed in from the top) back to where it was.

Now you know that the cable and driving gear are properly engaged.

Leave the speedometer end disconnected and visible from the driver's seat. Drive around the neighborhood and watch the inner cable. It should be spinning - it doesn't spin very fast at all but it should be a steady RPM.

If it spins, reconnect it to the speedometer head.