Lazy Speedo

[gilbert911]

Been out today and the initial 40 mile or so run was fine.
Car then parked for lunch for maybe 2 hours.
On the return journey the speedo needle seemed to stick at about 10MPH.
On the motorway the needle rose very slowly and I estimate from the revs and the speed of the other traffic that it was reading about 1/2 of my actual speed.
On slowing, the needle stuck at the highest reading it had achived.
On coming to a standstill at the bottom of the slip road it dropped abruptly from this point to zero (on the needle rest pin)
The rest of the jorney is usually a 40mph urban trip and again the needle never got past 10mph.
Any ideas what's causing this would be much appreciated.
The car is a '72T on Carbs.

[Alan @ CanfordClassics]

There are three parts (externally anyway) to the speedo working, the speedo gauge itself, the speedo cable and the speedo drive on the gear box. Disconnect the cable from the back of the speedo and have a look to see if everything is in order. New cables are cheap but if you need a new speedo gauge ask on here first. I have one or two spare.

Alan