HELP!! speedo stops and starts ????

hi can anyone help i have a 95 discovery 300 tdi with a annoying problem if the cars is used for lots of short trips (under 10 miles) the speedo works fine all day but if the car is driven for any longer trips without stopping the speedo jerks up and down and then just stops .... but if left for half an hour will work fine again has anyone had a similar problem and any ideas what it may be before i start changing parts (im hoping its just a worn speedo gear or something easy to fix thanks.

no lube and the cable heats up, expands and snags the outer case. when its cooled down its ok or if it dont have enuf time to expand?

ok what do i need to do ? is it just a case putting some lube on the end of the speedo ?

Don't lube the cable too near the speedo head, the grease or wotever can work its way up into the speedo and nertle it.