In short, is there anything besides the VSS possibly going bad that would cause a speedometer to bounce?

I did a search, but that was the only explanation I came across. I ask if there's anything else, because I just had to replace my speedometer cable after swapping clusters.

In more detail, here's exactly what happened. I bought a 145mph gauge cluster to replace my 85 mph indicator cluster.

I noticed before putting it in, that the speedometer would not turn freely by hand. I was going to just put my perfectly fine working 85 mph speedo into the cluster and install it. (I don't really care about the 145 vs 85 thing, I was doing the swap to get a tach and real gauges instead of the huge fuel gauge and idiot lights). Anyway, my brother turned the speedo with a pair of pliers, and against my better judgment I went ahead and installed it. Of course, it snapped my speedo cable after less than 30 seconds of test driving it.

So I order a new cable, put it in with what appeared to be no problems - routed the exact same way. However, now my 85 mph speedo, which was perfectly fine before, starts bouncing. It does this until it reaches about 25mph at which point it steadies - of course, I am actually doing about 35-40 at this point.

I couldn't remember when I swapped the speedo into the other cluster if I used my old VSS (the yellow box on the back of the cluster) or the one that came with the new cluster. So after reading up on here that a bad VSS may cause this problem, I swapped them thinking I may have left the one that came with the gauge cluster on there and it might be bad. It made no difference. It's still bouncing, and by my estimation, reading extremely low as well.

I don't think there's anything wrong with the speedo head itself - as I said, it was working perfectly fine before. So is there anything else I should be looking at that could cause it to be bouncing like it is? The installation of the cable seemed pretty straightforward and I can't imagine anything I did with that would cause this problem.

 

LUBE!

 

Is the new cable seated securely onto the speedo head? Could the old cable have caused a problem with the driven gear in the trans? Is the cable brand new?

JamesC

 

Yeah, the cable is brand new, and definitely clicked into place on the speedo head. I don't think the old cable could have caused a problem. It was fine with this speedo. It was snapped when I hooked the new speedo up to it, which was frozen - or rather close enough to frozen that the tension snapped it after about 30 seconds. Hopefully that wasn't long enough to do anything to the gear, but anything is possible.

I am guessing Stevenb is right and hopefully I just have to lube it. Seems obvious, but honestly it hadn't occurred to me being that the part was brand new and I'd never replaced one before, so didn't realize that should be done.

 

The new GM cable I used didn't require lubrication, I guess, because it performed as designed. I've lubed several cables with good results. I used a lube called Sil-Glyde from Napa, a product designed for speedo cables among other things. Pull the cable from its housing, shoot some brake clean on the cable, dab some Sil-Glyde in your palm and run the cable through it as you feed the cable back into the housing. With a new cable, I wouldn't think you'd need to clean the housing itself.

JamesC