Chrome type 12 dials used on 200 series and 300 series vintage GPO telephones can run slow over time. The instructions below explain how to safely take the dial apart to clean/lubricate the governor and gears to fix this problem. You can do this without removing the dial from the Bakelite case of the telephone (we have only removed it for clarity of the photographs).
1) Firstly NEVER EVER Spray WD40 or other oil directly into these old dials. The backing to the dial number plate (seen on photographs below) is similar to emulsion paint and is VERY porous. WD40 or other lubricants will soak into this, badly discolouring it and most likely destroying part of the numbers. We see more dials badly damaged by people doing this than any other cause.
2) Using a very small flat bladed screwdriver carefully prise out the metal circlip that holds the paper dial label insert in place (usually covered with a plastic clear label cover).
3) Remove the clear cover and dial lable to expose the centre screw.
4) Next remove the CENTRE screw (and only the centre screw) with a flat bladed screwdriver, and lift it off the chrome finger dial.
5) Carefully remove the larger circlip holding the number plate in position (looks like piano wire). I do this with a compass point, and I think this is the fiddliest part of the procedure.
6) At this point the dial number plate can be lifted out exposing the inner workings of the chrome dial.
7) Notice in the next photograph (below) the back of the dial number plate, which is the porous backing that WD40 or other lubricants will absorb into, and permanently decolour and damage. Be VERY careful not to get any oil near this part.
8) Use a cotton bud to apply (very sparingly) a small amount of watch makers lubricating oil or graphite to the inside of the governor cap (see below).
9) Next use a cotton bud to apply (very sparingly) a small amount of watch makers lubricating oil or graphite to the gear teeth (see picture below).
10) Reassemble the dial in the reverse order.
11) If you have been successful you should be able to dial a “0” and in the time it takes to say (at a steady pace) “one thousand one hundred and one” the dial should return to its rest position.