Speedometer increasingly bouncing? 1993 K1500

[1500z71]

Hey guys, been a minute since I’ve posted, hope everyone is doing well and Covid-19 free.

It’s not that big of a deal but I believe the occurrence is starting to increase.

I’ve noticed lately, and I don’t get to drive my truck that much at this point, like maybe a few times a month, that my speedometer is starting to bounce. It will readily bounce at any point that I put on the cruise control, and I’ve been noticing that it’s starting to do it every now and then on heavy acceleration. In both instances it’ll bounce and quickly correct itself and won’t be a problem again until I reset the cruise control. Again, it will very rarely, but increasingly so (the reason for this post) bounce under heavy acceleration. It’s not really a burden, but I’d like to try to get ahead of this before it gets worse like it looks like it may be doing. What might I be looking at or checking here?

Thanks guys, and be sure to wash your hands I guess! If this is the wrong forum topic let me know and I’ll move it.

Truck is a 1993 K1500 5.7 Silverado Z71.

 

[1500z71]

Bump

 

[1500z71]

Still have the issue. Aside from checking a few grounds, I haven't found anything. It seems to have plateaued for now. Stuck between this and some sticking lifters.

 

[jcg9393]

I have that same issue with the speedo needle, but mine only does it when I use the cruise control. Did you ever find the problem?

 

[1500z71]

I have that same issue with the speedo needle, but mine only does it when I use the cruise control. Did you ever find the problem?

Man I haven’t. Mine consistently only does it on cold starts and with cruise control just like yours. But if we both have the problem maybe it isn’t just a total fluke?

 

[jcg9393]

Man I haven’t. Mine consistently only does it on cold starts and with cruise control just like yours. But if we both have the problem maybe it isn’t just a total fluke?

I believe it is a grounding issue. I've found that if I turn the blower on High, it seems to either stop or greatly reduce the jumping of the needle. I haven't chased down where the ground points are, but maybe the speedo and the blower motor are grounded to the same location.