1978 280z Speedo Troubleshooting

[gotham22]

Hey Guys,  I replaced my speedometer cable and it worked fine for about two weeks. Now the needle doesn't move.  I checked the connection underneath the car and also at the back of the gauge.  It looks good.  If I remove the cable from the gauge and drive is that a good way to see if it is spinning? I have a dash cap and no easy way to remove the speedo unless I remove the dash which is not what I want to do.  So I am looking for an alternate way to test it before I go down that route.  I had similar issues with my other gauges and the fix was to take them apart and use fine sandpaper on the internal connections.  Could that possibly be an issue here?

[Yarb]

It’s a drive gear via the cable. No electrical involved. Reach your hand up there and disconnect it. The cable is slotted where it goes into the back of the housing. You may not have it seated properly.

[Patcon]

Yes, you could disconnect if from the speedo and see if it spins when the car moves.

Edited October 23, 2023 by Patcon

[Yarb]

@patcon, you’re thinking the drive gear in the trans might have an issue?

[Patcon]

Just trying to isolate the problem. If it spins, it's in the speedo. If it doesn't, it's a broken cable, damaged gear or a sheared pin

[Yarb]

Just wondering if he got it seated correctly when the cable was changed. Actually on both ends now that I think about it. Start from the bottom end first.

[Patcon]

The fact it worked for two weeks makes me think seating isn't the issue

[gotham22]

I will conduct a test in a few days and see if it spins as a first step. Thanks for the quick repsonses