Weavie Posted May 27, 2019 Share Posted May 27, 2019 When I recently rebuilt my1997 S3 Lotus 7 Caterham, I fitted a 5 speed gearbox and decided to go digital for the speedo, blanking off the speedo drive on the side of the box. I bought a speedo and sensor from Smiths and it has been a total failure to date. The sensor had to be so close to the prop shaft/diff bolts that it has been wiped off twice. The other fault, (when working in short periods), is that it seemed to develop an offset so above 60 mph, it would suddenly show 80 mph, and this offset would remain until the ignition was turned off and on again, not something I could do unless stopped. I am almost considering taking the engine & gearbox out to refit a speedo drive. Does anyone have any advice on the kit to use and where to safely mount the sensor?Many thanksSteve Link to comment Share on other sites More sharing options...
elie boone Posted May 27, 2019 Share Posted May 27, 2019 You can mount the sensor on the steering arm of the front wheel and the 4 bolts from the disc will be seen by the sensor. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 28, 2019 Member Share Posted May 28, 2019 Have you got a model number or similar for your current sender?Does it have a telltale light?...You can get an electronic sender which attaches to the mechanical drive from a Type 9 box. But it might or might not work with your instrument....Isn't it usually possible to change the drive without removing the gearbox?Jonathan Link to comment Share on other sites More sharing options...
elie boone Posted May 31, 2019 Share Posted May 31, 2019 Picture of the speedo sensor at the front wheel. this is an unshielded sensor that should be 8.5mm from the bolt but it needed a little bit closer than that before the telltale lights come on. Link to comment Share on other sites More sharing options...
Tony Whitley Posted May 31, 2019 Share Posted May 31, 2019 (Double post) Link to comment Share on other sites More sharing options...
Tony Whitley Posted May 31, 2019 Share Posted May 31, 2019 Isn't it usually possible to change the drive without removing the gearbox?Pretty sure blanking or unblanking the speedo drive can’t really be done in the car as it involves a gear shaft the width of the box. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 31, 2019 Member Share Posted May 31, 2019 Pretty sure blanking or unblanking the speedo drive can’t really be done in the car as it involves a gear shaft the width of the box.Ah... you can get to either side and fit the cap or the angle drive, but not the shaft?Jonathan Link to comment Share on other sites More sharing options...
elie boone Posted May 31, 2019 Share Posted May 31, 2019 Yes you can, to make life a bit easier unbolt the 2 bolts that hold the gearbox mounts so you can slide the box from side to side making more room to work. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 31, 2019 Member Share Posted May 31, 2019 A bit more, please, Elie... can you replace the shaft without removing the box?ThanksJonathan Link to comment Share on other sites More sharing options...
elie boone Posted May 31, 2019 Share Posted May 31, 2019 The plastic speedo drive can be taken out as it sits in an angle of about 45 degrees, BUT be care full as you place it back in the gearbox because it can be placed next to it's guide and then it's a real fiddle to get it back out of the gearbox, feeding a screwdiver or 3mm wire from the other side is good to pilot you trough the right angle.and on top of that all this can be done on axle stands. Also i did heat up a screwdriver and bent the tip 45 degrees to make it less difficult to pop off the top cover. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 1, 2019 Member Share Posted June 1, 2019 ThanksJonathan Link to comment Share on other sites More sharing options...
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