6 replies to this topic

[Mini Mad Drakeley]

hi

basically my speedo decided it wasnt going to tell me what speed i was actually doing, when i was stopped it went up and down from 0-20 and continued doing that at any speed, at one point it said i was doing 90 and i cant have been doing more than 50

im not sure if it my speedo or if its the speedo drive thing from the back of the engine, does anyone have any clue as to what it might be? i would rather get this fixed asap

i forgot to add, i have a centre binnacle dash so its one of the big type speedos

thanks, Adam

Edited by Mini Mad Drakeley, 05 February 2013 - 11:07 PM.

[KernowCooper]

Broken cable jumping or maybe the speedo head its self? disconnect the cable first and have a look at it

[dklawson]

+1 on checking for a broken cable. That is your least expensive option.

The gauge should not read any speed at idle since nothing would be turning. There are only two reasons the gauge would display a reading when the car is standing still.

• The cable is broken and wedging "upward" against the input/drive end of the speedometer or
• The needle bearing at the bottom of the shaft the pointer is on is contaminated or dirty.

The speedometer cable is an easy and relatively inexpensive DIY thing to try first. If that does not address the problem, disconnect the cable as soon as possible to eliminate any possible damage to the gauge. Remove the gauge when practical and send it in for cleaning and calibration. If the lower needle bearing is dirty you do not want to risk it binding on the shaft which will send the pointer all the way around the gauge face. When that happens the repairs become more expensive, often justifying replacement rather than repair.

[Mini Mad Drakeley]

i had a chance to investigate and the end of the speedo cble that goes into the speedo looked pretty mangled so i have a new one on order and the current 1 is removed to prevent any damage to the speedo unit, il update this wether or not it cures the problem

thanks, Adam

[dklawson]

Hopefully the new speedo cable will fix this for you. You are not supposed to apply a lot of lube to the place where the cable enters the back of the speedometer. However, if the top of your cable was mangled, that may be a sign that a drop of 30W oil on the entrance to the speedometer is in order. Just a drop or so mind you and do not spray any lube up there.

[Mini Mad Drakeley]

just to update this, got and fitted my new speedo cable and it still doesnt work so im considering just getting a new speedo as i was never convinced it was accurate and estimated it was at least 15mph too high

link

im thinking getting this as the guessworks engine number thing says i have a final drive of 3.44, im guessing this would be the right one?

Adam

[dklawson]

I would not go by the engine number alone as the gearbox and/or final drive may have been changed... unless of course you know for a fact that it has not . You can determine the final drive and use the information on John's site to confirm what speedometer you need.

However, another way to determine which speedo you need is to remove the old speedo and put a piece of tape on the end of the cable to act as a flag. Then you SLOWLY drive a known distance while your passenger watches the flag and counts how many times it goes around. Knowing the number of turns for that measured distance you do some simple scaling math to determine how many cable (flag) revolutions you would have per mile. That number will be the turns-per-mile (TPM) number that your replacement speedometer needs to be. You will have a bit of an error in your measurements and calculations using this method but when you calculate the TPM number it will be pretty obvious which Smiths speedometer is close to your calculations.