MartinH Posted November 11, 2012 Share Posted November 11, 2012 Went for a pilgrimage to Aston Hill today as it could be the last blat of the year. It's about 20 miles from my house. Zeroed the mileometer, slithered up the hill and drove home. However, the trip was only recorded at 10 miles when I got home!!! And there was I thinking what feeble mileage I have been doing every year since I got the car...and also what rubbish miles to the gallon I have been getting. What a ****! What's wrong and how do I fix it? Cheers Martin Link to comment Share on other sites More sharing options...
EFA Posted November 11, 2012 Share Posted November 11, 2012 And what cheap insurance and low depreciation.... If your speed is indicated correctly, you need a new speedo. Link to comment Share on other sites More sharing options...
Area Representative Paul Richards Posted November 11, 2012 Area Representative Share Posted November 11, 2012 Get a bike speedo Link to comment Share on other sites More sharing options...
MartinH Posted November 11, 2012 Author Share Posted November 11, 2012 *arrowup*That did cross my mind Arnie but would rather have it right. Unless I was doing 140mph on the M40 on the way home then I am pretty confident the speedo is correct. I guess the speedo and mileo take their feed from the same sensor in which case, maybe the thing is fecked. Are there no switches or whatever on the back to change any settings? Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted November 12, 2012 Share Posted November 12, 2012 What vintage is the car - is it driven by a mechanical cable, or electronically ? Electronic ones have settings - some with switches under the big rubber grommet in the back, some by pressing the button on the front. Caerbont site had switch setting tables in the past - that's how I found mine had the switches set wrongly. But, as Arnie said - the speedo and odometer are fed from the same source. Link to comment Share on other sites More sharing options...
MartinH Posted November 12, 2012 Author Share Posted November 12, 2012 Thanks SM25T. It’s a late 2009 Duratec R300 SV kit. Speedo is black with white Caterham branding. So it is a ‘Caerbont’ is it? I will have a look at the back of it and maybe try and contact the manufacturer. Cheers, Martin Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted November 12, 2012 Share Posted November 12, 2012 Here is one page Caerbont ... and here is another Link to comment Share on other sites More sharing options...
lavena Posted November 12, 2012 Share Posted November 12, 2012 As said above depends upon electronic or mechanical. The electronic one can have a disconnect between the two - the odometer counts each pulse from the sensor and uses the number entered in the meter to calculate distance. The needle is effectively analouge and it can miss a few pulses but the needles just "jitters" a bit or drops very slightly. I had an issue where is was about 20% low in the distance, but accurate on the speed. The sensor was a little too far away and was missing 20% of the teeth so 20% less pulses. Andy Link to comment Share on other sites More sharing options...
LazerBrain Posted November 12, 2012 Share Posted November 12, 2012 I had a similar issue on a mk4 Escort with mechanical odometer and trip meter. In my case something had stuck when I pushed the reset button and the trip meter sat clicking on 0.0 for several miles until it started turning. I only noticed as I used to run with so little fuel and calculated when to refuel based on the trip meter. The result was a walk to the local petrol station... Did you notice the odometer reading before and after - did it increment by the same amount? I'd suggest checking that when you have a moment. If you have a smartphone then you could download a GPS speedo app, some of which have elapsed distance functionality, or consider driving between a couple of motorway junctions (where you know the distance between them.) Link to comment Share on other sites More sharing options...
John Vine Posted November 12, 2012 Share Posted November 12, 2012 Your car will have the programmable stepper-motor speedo. The first thing to check is the air-gap between the sensor and the reluctor ring on the OSR driveshaft. It should be somewhere around 0.5mm and (with the ignition on) the sensor should light up as each tooth passes by (see here). Next, check the calibration. Switch on the ignition while pressing the little black button on the speedo face. After 3 seconds or so, release the button. The display will show six digits. This value is the pulses/mile from the sensor. Assuming you have CR500 195/45-15 tyres, this should be 039751. This is a starting point, and you can adjust up or down according to real-life road mileage. I ended up at 040943. To adjust, see here. JV Link to comment Share on other sites More sharing options...
MartinH Posted November 12, 2012 Author Share Posted November 12, 2012 Hi JV, thanks for the post. This looks like its got legs. I quickly tried pressing the black button while pressing ignition and you are right - it looks like the programmable type. Mine read 39751. Haven't got time tonight but will investigate more thoroghly in the next day or two. The wierd thing is the speedo is reading correctly I think - its just the mileometer and trip recorder that seems wrong. Cheers, Martin Link to comment Share on other sites More sharing options...
John Vine Posted November 13, 2012 Share Posted November 13, 2012 That does seem weird, Martin. If the calibration is correct and the speed reading is OK, I can't think why the mileage reading should be so far out, other than the speedo itself being faulty in some way. Sounds like a call to CC or Caerbont is needed. When I was struggling to fix my speedo problems, James Gibson at CC offered to send me a new speedo to try out. It proved to be the answer, so it might be worth asking him if he'd do the same for you. JV Link to comment Share on other sites More sharing options...
garybee Posted November 13, 2012 Share Posted November 13, 2012 The [sPA] speedometer in my Ginetta works in an odd way that could be related to your issue. It uses a hall effect sensor for it's pickup and the speedo' has an adjustment on the back to calibrate the speed reading. This only effects the speed reading however, the odometer works solely on the pulses from the sensor. The speedo has a required signal frequency (at 100mph) marked on it. I had to make a toothed disc for the driveshaft that would show the correct number of 'teeth per second' to the hall effect sensor at that speed. Anyway, is it possible that your speedo' works in a similar way? Link to comment Share on other sites More sharing options...
John Vine Posted November 14, 2012 Share Posted November 14, 2012 Interesting thought, garybee. Like your speedo, the Caerbont unit is driven by a Hall-effect sensor, but if you alter the calibration value (pulses/mile), both speed and mileage readings change accordingly. JV Link to comment Share on other sites More sharing options...
lavena Posted November 14, 2012 Share Posted November 14, 2012 As I said, I had a similar issue with my speedo - speed was fine but tripmeter was under reading. If the gap between the sensor and the teeth is too much and the teeth is not perfectly circular then the sensor doesn't pick up all the teeth. The odometer counts the pulses so if it drops some it under-reads. The speedo is analogue (a needle) and if it misses one it will start to reduce speed but as it drops it gets another series of pulses so you don't notice the reduction. I would suggest checking the gap and reducing it to see if it improves the situation. Andy Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now