Tipidave Posted June 2, 2023 Report Share Posted June 2, 2023 (edited) Hi all , My speedometer failed soon after the installation of a d type overdrive to my 1967 Herald convertible. The speedo was professionally overhauled about a year ago and had been working fine before the overdrive installation. First symptom after just a couple of miles was that the speedo needle refused to settle below 20 mph. Then the speedo stopped working altogether. I released the cable at the speedo end and the needle dropped back to zero whereupon I reinserted the cable and tried again... the speedo didn't register any speed, although the odometer is registering. I have since installed a new cable (having been advised that the original had too much core showing). The Speedo now only works if the cable is backed off a bit and now (with it backed off)... I have a situation where the Odometer reads correctly but the speedometer (albeit steady) over reads by approx 10 mph up to 35 mph and then 15-20 mph between 40 and 55 (as measured against a phone based gps app). The fact that the odometer is plumb bob on would indicate the correct TPM and that the cable is turning correctly? I am a bit confused... Might I have damaged something inside the speedo head? I would be interested in your collective views/ experience in respect of diagnosis and possible prescription to fix.. Edited June 2, 2023 by Tipidave addition Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 2, 2023 Report Share Posted June 2, 2023 next time some says the cables wrong length inner you can wind the spiral case with grips to lengthen or shorten the outer case to give the correct inner protrusion to engage fully the oddometer is a simple pawl and ratchet operated off a worm on the main shaft its not connected to the needle readings what does happen is the main shaft wears and allows the needle disc drive to make contact with the magnetic plate or oil has contaminated it easy to inspect if you remove the bezel pop the glass out and undo the two screws in the back the assy will come out quite easily. dont strip any thing down and never remove the needle but a spray of brake cleaner may clean things up ok.if the disc is catching some gentle work may clear it Pete Link to comment Share on other sites More sharing options...
Tipidave Posted June 2, 2023 Author Report Share Posted June 2, 2023 Thanks Pete. Do you happen to know (or know where I can find details of) what length of inner cable is needed to engage properly and what maximum length can be so as to avoid Interference. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 2, 2023 Report Share Posted June 2, 2023 firstly with OD do you have the angle drive fitted ??? if so it needs any 7/16" dia washer between the drive and the OD pinion to avoid pre loading the drive . as for how long its trial and error the inner should be long enough to fit the speedo spindle but not too long to cause a preload on the speedo when you do up the knurled nut sort of just nice Pete Link to comment Share on other sites More sharing options...
Tipidave Posted June 2, 2023 Author Report Share Posted June 2, 2023 Thanks again... Yes it has the angle drive and yes it has the washer fitted... I think I will remove the speedo and 'fettle' with it out of the dash. Link to comment Share on other sites More sharing options...
RedRooster Posted June 2, 2023 Report Share Posted June 2, 2023 Think you have moved the magnetic pick up cup in the speedo, I had a similar thing a few years ago. Take the speedo apart and use a bit of the old cable in a drill to run it up, you will see if it's rubbing. RR Link to comment Share on other sites More sharing options...
Tipidave Posted June 6, 2023 Author Report Share Posted June 6, 2023 Will do thanks…. Going to wait until return from Le Mans classic at end of month for fear of breaking it before the trip!!! Link to comment Share on other sites More sharing options...
johny Posted June 7, 2023 Report Share Posted June 7, 2023 I seem to remember the cable can be installed the wrong way round or am I dreaming? Link to comment Share on other sites More sharing options...
68vitesse Posted June 7, 2023 Report Share Posted June 7, 2023 I believe speedometer has metric thread and angle drive has BSC and not close in size. Regards Paul. Link to comment Share on other sites More sharing options...
johny Posted June 7, 2023 Report Share Posted June 7, 2023 Yes youre correct, my memory! What you can do though I think😳 is pull the inner out some from the sheath at the speedo end (this disengages it from gearbox but not a problem). Then insert the end in the speedo drive where it should enter right up to the backstop flange of the inner. If it does this then the inner tip isnt too long and cant put pressure on the speedo internals. However if the flange wont sit flush with the speedo drive youre forcing it in as you do up the sheath nut! If theres nothing obstructing the speedo drive hole the solution is to grind off a little of the inner tip until it will fit correctly. Once done rotate the inner while pushing it back in the sheath until it re-engages with the gearbox... Link to comment Share on other sites More sharing options...
Tipidave Posted June 7, 2023 Author Report Share Posted June 7, 2023 Thanks for the detailed description. Very useful 😀👍 Link to comment Share on other sites More sharing options...
Tipidave Posted June 8, 2023 Author Report Share Posted June 8, 2023 (edited) So… having said I will wait until after my Le Mans trip… I have made some progress. I ground a few mm off the cable at the gearbox end and having checked a “spare speedometer” on the bench also removed a couple of mm from the speedo end. The good news is that the spare unit seems to work correctly (although my be slightly off in speed) when it it just dangling in the car and not fitted… that’s the next job. But before I do I need to remove the bezel and clean the glass on both sides. the bezel has already been attacked in a previous life and could do with a replacement. so does anyone know where I can get a replacement bezel at reasonable cost? Edited June 8, 2023 by Tipidave Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 8, 2023 Report Share Posted June 8, 2023 i did say you dont need to cut the cable you just twist/untwist the outer case its spiral wound so rotate with grips will make the outer longer or shorter it is a common fix as for a bezel its second hand unit and hope its better there are new around its still made by Cearbont instruments to smiths design Pete Pete Link to comment Share on other sites More sharing options...
Tipidave Posted June 8, 2023 Author Report Share Posted June 8, 2023 Hi Pete the end of the cable was damaged hence decision to recut the end😀👍thanks for reply again Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 9, 2023 Report Share Posted June 9, 2023 19 hours ago, Tipidave said: so does anyone know where I can get a replacement bezel at reasonable cost? New will be hard to find due to the (probably) unique size of the gauge. They come up on eBay all the time S/H - there's one currently selling for £19.99; just buy another unit and swap over. The rubber seal can be bought by length, wind round the bezel and cut to fit. Avoid the NOS versions; I remember Rimmers selling those off for pennies a few years back (I bought two, still boxed and as yet never fitted) but some enterprising sellers are asking £199 whilst others are a more modest £96. Link to comment Share on other sites More sharing options...
Josef Posted June 11, 2023 Report Share Posted June 11, 2023 Fitchetts might be worth a ring in case they have a stash hidden away somewhere. Link to comment Share on other sites More sharing options...
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