SPEEDO QUESTION

[thecount]

Good day everyone

Wonder if you all may be able to help me with a question relating to the speedo please. The Count is a 1955 4dr, originally a 803cc, though now has a 948cc with a 4.5 diff and still maintains the 803 gearbox. The speedo I have in the car is a gold face, though it only has three lights on it ( high beam, oil, ignition) and a 5 numeral mileometer. I am fairly certain that the speedo is totally incorrect for the car and it frustratingly seems to read about half of what the actual speed one is travelling at. I am fairly certain I need to have a 4 light 80mph speedo, but given that does anyone know if there is one that may read fairly much correct given the cars current mechanical configuration or am I better off buying any 4 light and tying to find someone to recalibrate it?

Thanks for your time and advice everyone

Gav

[bmcecosse]

The 803 would originally have a 5.3 final drive ....so now with 4.5 the odometer will be wrong by that ratio. What tpm is the speedo in the car at the moment? 1000 ??

[IslipMinor]

The 803 gearbox has a different speedo drive ratio on the tailshaft to the later 948/1098 boxes. It is 4.5:1, so the speedo cable revolves much more slowly than the later 2.6:1. The correct speedo should have 1000 on the face, but that is for a 5.375 rear axle ratio. If you have a 4.55 diff, then the correct turns per mile, will be even less at 847 - unfortunately, they do not exist as far as I know.

Looks as if you could swap the speedo drive worm and wheel with the later 2.6:1 ratio parts, and then use a speedo with 1504 tpm, which is the standard 948 head.

Alternatively, if you don't mind the odometer being out and under-reading, you can always move the needle round a bit? Open the speedo head up and remove the glass, then hold the aluminium disc on the back with the needle pointing at, say, 60 mph, gently twist the needle to remove it and replace it pointing at 71 mph, you will get roughly the right speed for your 4.55 diff!

[thecount]

Thanks very much for your advice bmcecosse and Richard, very much appreciated

Looks like it will be of to an instrument tech for a total recalibration

or maybe just moving the needle

Thanks

Gavin

[bmcecosse]

That's likely to be v expensive - whereas a change of speedo could be cheap - but I do appreciate where you are.... I ask again - what's the tpm number on the speedo?

[David W.]

Measure a course of 52 feet, 9+3/4 inches. (1/100 of a mile)
Pull the speedo out to access the cable.
Stick a paper pointer on the speedo cable.
Drive the car slowly along your course and count the turns.
Multiply by 100, and that's the turns per mile (TPM) you need for accuracy. (This accounts for everything, diff ratio, tyre size etc.)
Find a speedo with the closest tpm.
Above the odometer you will see numbers: S/N XXXX/YY ZZZZ
The last 4 digits are the tpm for that speedo.

[thecount]

Hi again

bcmecosse, sorry I don't actually have the car with me at the moment, it's stored a mere 27 hour drive away from my home, so will have to get back to you with that once I get my hands on it again in the relatively near future.

David W. doesn't sound too difficult, though I am sure I can stuff it up. I will have to have a go at that and see what I can find out!

Very much appreciate all advice, I was hoping it would be an easier situation, though I am sure once I get the car back home I can move forward with this. I'll let you know!

Thanks very much again everyone

Gavin

[bmcecosse]

27 hours......geeezzzzzzzzzz

[don58van]

Australia is a bit bigger than the UK

27 hours? Pffffft. Just a run to buy some milk.

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[thecount]

Great map! Yeah a wee 27 hour drive is nothing but a shake down run really, as a kid the family used to drive from Melbourne to Mackay in North Queensland regularly, so I guess you get used to "small" trips like that. I

t's only inconvenient when you actually want to do a quick bit or work on the car