Ive got a 93 T100 and the speedometer will stop working intermittantly. The odometer will be turning, but not the speedo. Seems to happen more often during rain. After driving about 10 or so miles it will just jump up to the current speed and work from then on out. Any ideas?

 

Almost forgot, v-6, 5speed tranny.

 

Is it a mechanical or electronic speedometer (electronic one will have a VSS attached to the transmission or transfer case). If electronic, check for loose connections in the wiring that may be allowing water in, that could cause the signal to drop out as you describe.

 

You need a new speedo. If it was the VSS wiring or sensor you would not be able to have a working odometer. This tells you it is getting a signal from the VSS. The little electric motor for the speedo failed.