Speedo calibration

Hi,

Does anyone have a clue how to go about re-calibrating a Smiths Speedo? Can I do this myself or is it something I need an expert to do?
The cable was disconnected when I purchased my car, (Found to be broken) but a new one was made up and this has now been replaced and reconnected.
Problem now is when Im cruising at 100km per hour it shows 180 km's etc. the needle also "wanders" not unlike my brain when out the corner of my eye, I keep seeing the needle jumping around
I pulled the speedo out and it doesnt look too complicated.


Many thanks
Don.T

It can be 1 of a 3 things

1. The wandering of the needle suggest that it is internal problem in the guage. However,

2. If the gear in the transaxle is broken, or missing a teeth and is jumping around spinning when it catches.


Pull the cable off the tranaxle and check the gears. If broken, replace the gear. Calibration
depends on what gears you have in the transaxle and tire size. Check the gears first....if it isnt broke, pull the speedo out and have it checked. Or it could be both...If the gears are broke. and you run the speedo with the broken gears it will mess up the springs in the speedo.

regards
oliver

The speedo cable is very long in most 40's. It is very common to have some wind up in the cable. This causes the fluctuating needle.

Thank you for the advice. /ubbthreads/images/graemlins/smile.gif

Don T,

The most probable cause for a fluctuating needle is lack of lubrication or tight spot along cable. Make sure you have routed your cable smoothly and supported it "loosely" and injected plenty of lubrication throughout.

Despite its length, a properly laid speedo cable will cause no problems.

Graham @ GTA Racing.

Hi Don.
I do not know where you are located, however this should help you resolve your problems.
You need a ratio adaptor to correct your speedometer. The adaptor can be fitted on the back of the speedometer gage or on the transaxle where the cable enters. United Speedometer Service in Roverside California make the adaptors and also custom cables. see the following web site.

http://www.speedometershop.com/rep-pag.htm

On there web site they have a page called "Ratio Test". It indicates how you chech the ratio of your existing set up, and how to order your new Ratio Adaptor.

I baught my adaptor in 2001 and at the time it was $66.00 They are not expensive.
This company is good to work with and very helpfull.

The best lubricant for a cable is molybdenum disulfide (dry film lubricant) It is available in powder form. The powder is best if you can get it into the cable because the dry powder does not attract dirt like an oil would. The powder is also recommended for locks for the same reason. see the following wewb site.

http://www.goldtown-phils.com/lubricants/graphite.htm

Hope this helps

Juts a final possibility. The speedo itself can be at fault if it is old. Some older speedos use a design whereby a magnet spins in very close proximity to the needle armature (I may have the terminology wrong here). If this magnet is no longer an equidistant from the armature as it spins (possibly due to ware or corrosion) it can cause the magnet to pickup the armature too early and “throw” it forward. This happened to two old cars that I owned and in both these cases the needle jumped around and showed a higher speed reading. In one case I could hear a quiet "chuff chuff" sound as the needle was thrown forward.