Speedo Problems

[DBlake]

My speedo has almost died. It works until about 35mph sometimes a little higher, then drops to zero. After I come down below 30 it starts working again. I have the GV Overdrive and therefore two VSSBs. The speedo is not affected by the GV kicking in and switching VSSBs. Also the cruise control works fine. Upon recommendation of the GM service guy, I ordered a new and changed out the GV supplied VSSB to see if that helped - no difference. I think its an instrument cluster issue. Any ideas? I plan to see if I can find a used instrument cluster unit tomorrow and switch it out. Also, when the Speedo drops out, the odometer also stops. Thanks for any thoughts

[a5150nut]

And the worst part is the cruis control quits too! I went thru some of the same problems. Replaced ths VSB after replacing the speed sensor. Did all the checks by the book. Ended up being the speed sensor I put in "NEW" was also bad. Good thing is the VSB has been calibrated to read correct with my 285's. Check all conections, and get a digital meter to do all the checks in the book. It can get costly replacingg the cluster. I was told $325 exchange at the dealer.

[DBlake]

My difference is the cruise control works fine. That leads me to believe the problem is either the VSSB or the instrument cluster, not the speed sensor on the tranny. I am trying to talk to Gear Vendors as their electronics interfaces with the speedometer function. This is one of those times 3rd party equipment makes it very hard to track down the actual problem. IF I figure this out I'll post the solution.

[DBlake]

Just to let anyone who had been following this know - the problem turned out to be the speed-sensor on the tail shaft of the Gear-Vendors overdrive unit (they use a GM Turbo 400 speed-sensor). I have to say that I have learned more about the GM speedo system than I care to. The GV folks were very helpful in trouble-shooting this even from a distance.