Chevrolet Repair: !990 Chevy, 4 wd, tranfer case

Question
Hi Mark, Also have a 90 that the speedometer stops working as I am driving down the road than it will start up again than it may stop again or it may stay working for awhile. I have changed the sencer on the tranfer case several times with the same resultes.
         Thanks Again Ernie
PS 4X4 5 Speed 350 1/2 ton 1990
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Followup To
Question -
I have a service 4 wheel drive light that comes on and stays on after driving it for awhile.I have checked all fluids in drive train they are all full. Any good ideas?
         Thanks Ernie
PS Ext. Cab Silverado 4X4 Gas 1999
Answer -
Hello Ernie, The most common thing here is the switch for the 4 wd. These go bad a lot. Without being able to check for codes in the system, I would first replace the switch in the dash.

        Mark

Answer
Hi Ernie, If you have changed the speed sensor then the problem might be in the cluster. There is a motor in the speedometer that might be cutting in and out. There is a buffer that sets behind the glove box that could also be a problem. It is a white box that is just to the left of the glove box. Sorry I can't give you more on this.

         Mark