Speedometer (round type)

Phil Robson

Phil Robson

Well-Known Member
I have acquired several speedos to replace BOP's that flicks all over the place. Firstly a 'new' one that I can't get to work (it does record the miles) & another used one that seems to read about 5% low.

Does anyone know how to fix them? They seem to operate by a magnet spinning against a sprung disc:

Magnet:

IMG_7237.JPG

Sprung disc:

IMG_7238.JPG

On all speedos the action seems to be the same (resistance to movement etc) yet the new one doesn't work when it's in the car :(.

Also, the one that works the best (used but steady) reads a bit under the correct speed, yet it has the same serial number on as the others. I appreciate that the 4-cylinder ratio is different to the V8s.

Any ideas guys?
 
All the Smiths speedos of the period have the same mechanism inside.
Needle flicking could be either problems up the speedo input (worn angle drives, sticky, binding cable) or problems with the speedo itself. If there is a problem with the speedo, you can take them apart at home and improve the flicking issue, but since in contrast with the professionals you cannot check the accuracy, you should not be very demanding in this area. In order to take them apart, first you have to pull the needle off its spindle, but first mark the position of the drum with the needle at zero, other wise at reassembly the preload of the needle will not be correct. With the needle off, usually it takes only two small screws to take the face of the speedo off. With the face off, the front of the mechanism is exposed, and you can see how the spinning magnet drags the drum that is connected to the needle spindle. A flicking needle is normally caused by excessive drum endfloat. You can tight it up a little (i don't remember how you do this now, it has been a good few years since i took one apart, but i think that it was obvious...) and check the results driving the speedo with a drill, without assembling it. Needless to say that drum endfloat also affects accuracy, so don't get too much carried away. While you are there some watch oil in critical moving parts will help.
Your non working new speedo must have a stuck drum, so if you take it apart, you could possibly free it carefully.
I bought a fitted a new strip speedo for my series 1 TC, when i first got the car back in 2006. Now it is approaching to get for a second time around the clock, and its still nice and steady. Given the bad reputation of the round speedos, probably by the time they appeared the assembly procedure was somewhat careless.
 
Phil Robson said:
I have acquired several speedos to replace BOP's that flicks all over the place. Firstly a 'new' one that I can't get to work (it does record the miles) & another used one that seems to read about 5% low.

Does anyone know how to fix them? They seem to operate by a magnet spinning against a sprung disc:

Magnet:

View attachment 15607

Sprung disc:

View attachment 15608

On all speedos the action seems to be the same (resistance to movement etc) yet the new one doesn't work when it's in the car :(.

Also, the one that works the best (used but steady) reads a bit under the correct speed, yet it has the same serial number on as the others. I appreciate that the 4-cylinder ratio is different to the V8s.

Any ideas guys?
Click to expand...

Hi!

My speedo had been underreading since i bought the car in 1983. At a period of unemployment in 2006, I decided to test the speedo with an old drill and a clock (see the "equipment" in picture). "Drive" 2 km on the trip counter and measure the time. The result of the speed measurement was an average speed of 129 km/h with a needle pointing at only 109 km/h. The way I regaussed the magnet can be seen in the other picture. The cable was connected for a fraction of a second to a "pulse" from the car battery. The result was a needle pointing at 140 km/h at the same test as above. To adjust the needle to a more accurate reading, I took away the needle and turned the attachment fixing while holding the "drum" with my fingers. The result of this adjustment was accurate readings at higher speeds (70, 90, 110) but at 50 or lower it undereads by approximately 3 km/h.
I am pleased with the results, but a speedometer workshop would have done it better, having degaussing equipment to adjust the speedo instead of my way to turn the needle fixing.

Best Regards: Göran Olsson (Rover Club of Sweden)
 

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I used to work for Rediffusion, in the TV rental section. Every now & again someone would put a hi-fi speaker next to their set & all the screen colour would gravitate towards the magnet, then we'd get the call & take the big old degaussing coil round & after moving the speaker, we'd plug it in, & switch it on in front of the screen then move it in a circular motion while walking away from the screen. The customers were always amazed as the colours danced around the screen until they all settled back into their rightful place.
All good, old-time fun.
 
The Rovering Member said:
I used to work for Rediffusion, in the TV rental section. Every now & again someone would put a hi-fi speaker next to their set & all the screen colour would gravitate towards the magnet, then we'd get the call & take the big old degaussing coil round & after moving the speaker, we'd plug it in, & switch it on in front of the screen then move it in a circular motion while walking away from the screen. The customers were always amazed as the colours danced around the screen until they all settled back into their rightful place.
All good, old-time fun.
Click to expand...


ha ha, i remember when i was a teen my mate and i made his dads tv go all funny with a magnet, then realized he would probably kill us!

took me bloody ages, but using the same magnet i managed to "pull" the picture back correct again
 
It was about the only technical job l could do on the things. After starting as a fourteen year old van boy on Saturdays l eventually became the full-time installer. They sent me on day-release to college & to technical courses at the company schools but the insides of the TV's interested me far less than the showroom girls & the customers daughters (who were never locked up when l called :p).
I did get a pass with credit on the City & Guilds course year one but my manager ventured to suggest that if l had got a credit then the rest of them must have got bloody George Medal's. Scottish insightfulness at it's finest as you only had to memorise in the first year. From the second you had to understand what you were writing down.
A good man though, l wasn't supposed to have a second job but when the darts team he ran turned up for a match at the pub l was moonlighting in (The Prince of Wales at the Hatch for Harvey's reference), he greeted me warmly & bought me a half. Brings a warm glow of rememberance that does, they were halcyon days indeed with grand workmates & a company Transit to boot (& some lovely girls ;)).
I claimed redundancy when Granada took over, stayed with the highways & eventually headed to the lorries.

Sorry, l've hijacked this thread.
 
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That name rings a bell but l don't recall actually going in & having a look.

Many people used to come in The Prince just because the table was there. I don't recall ever seeing another pub with a full-size one. A proper old public bar/saloon bar pub with a lot of regulars & generally speaking the customers nearly always used the same bar. There wasn't a lot of inter-bar migration. Tom & Queenie who ran it were a proper old-time pub couple. They retired to Enterprise House. I had a second stint in there after leaving the first one & it had been taken over by an ex-trucker & his wife.
Long gone now.
 
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