Flaky speedometer

[kilroy]

If you have had this problem please tell me what you found and what you did it fix it. My speedo works about 90% of the time, but sometimes while driving it will quit, the needle will just drop to 0 or 25 or go up to the max peg, when it does this the odometer quits working no matter where the needle comes to rest. Then it will start working again, generally within a mile or so of when I notice the problem. Nothing else in the dash or any where else in the truck seems to be affected. I have only noticed this when I am going highway speeds (95% of my daily traveling). 90 GMC Jimmy with stock 350 TBI and auto trans
Thanks
Tramp

 

[Blazer_Boy]

Probably electrical because I believe they switched to that style in '90. The trasnfer case should have the sender, try changing that. You may have a short or something. You loose the signal and it will falls, if it gets grounded and it pegs.