Leadership Team Garry7 Posted March 17, 2014 Leadership Team Share Posted March 17, 2014 Speedo failed on a Blat weekend before last, roads were wet and muddy. Cleaned the toothed wheel on the osr driveshaft and cleaned the sensor head. Speedo worked for about 5 miles then quit. Over this weekend worked for first few miles after starts then quit. Any suggestions gratefully received. Thanks Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted March 17, 2014 Share Posted March 17, 2014 On Mike Clark's, it was an over-long cable to the OSR wheel speedo sender .... cable tied to the chassis tubes ... chafed through ...... and ended up immobilising the car too. Link to comment Share on other sites More sharing options...
Martin J Posted March 17, 2014 Share Posted March 17, 2014 What is the clearance between sensor & toothed wheel Garry? It needs to be close as possible without making contact, ie about 1mm. Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted March 18, 2014 Author Leadership Team Share Posted March 18, 2014 Thanks Martin, its set at about that - guess its a new sensor then? Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted March 18, 2014 Share Posted March 18, 2014 Just a thought ..... is there any difference in gap between car jacked up and with wheels on the ground ? Perhaps you can lower it gently onto something under the brake disc to simulate this ? Link to comment Share on other sites More sharing options...
John Vine Posted March 18, 2014 Share Posted March 18, 2014 You can check the sensor by jacking up the OSR, switching on the ignition, and then rotating the wheel slowly. As each tooth on the reluctor ring passes the sensor head, the sensor LED should light up. IME, the sensor itself is a reliable unit. As others have said, the air gap is critical (typically in the 1 - 2mm range), and so is electrical continuity (no broken or frayed wires, good earths). It could just be, of course, that you have a faulty speedo. That was the eventual diagnosis in my long-running speedo saga (here). Another thought... do you have a rear ARB? If so, you might want to check that you have the latest ARB mounting brackets (as described in Workshop Notice 460 -- see here). JV Edited by - John Vine on 18 Mar 2014 10:34:39 Link to comment Share on other sites More sharing options...
swsambler Posted March 18, 2014 Share Posted March 18, 2014 Had the same problem with my 2010 build 175 Roadsport. Speedo used to fluctuate and then go to zero above 50/60mph. It would then recover as speed dropped and continue to fluctuate. I tried all the clearance, cleaning, electrical continuity, mount flexing and pulse recomendations to no avail. Instantly cured by fitting new sender and lead. Good luck. Link to comment Share on other sites More sharing options...
John Vine Posted March 18, 2014 Share Posted March 18, 2014 Quoting sambler: Instantly cured by fitting new sender and lead.Did you happen to notice whether the old lead was damaged in any way? JV Link to comment Share on other sites More sharing options...
Michael H Posted March 18, 2014 Share Posted March 18, 2014 The sensor really needs to be as close as possible to the toothed ring otherwise I find the speedo begins to drop out at high speed. Mike Link to comment Share on other sites More sharing options...
redlight Posted March 18, 2014 Share Posted March 18, 2014 I have had the same problem on my 175 S3 Roadsport twice, the cure was a new (expensive) sensor from Caterham. I could not see any damage to the old units when I took them off. I got a 1 mm strip of plastic to use as a feeler gauge, but always set the gap with the power off. Good luck Edited by - redlight on 18 Mar 2014 16:27:39 Link to comment Share on other sites More sharing options...
myothercarsa2cv Posted March 18, 2014 Share Posted March 18, 2014 Is it possible to swap to the gearbox driven speedo? Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted March 18, 2014 Author Leadership Team Share Posted March 18, 2014 Thanks all for the advice / experiences 😶🌫️ JV - wire does not appear damaged in any way Mike - it's as close as I dare, last year it did as you describe, just when you really need it! MOCA2CV - like your thinking! I have no idea tho. Red light - looks like it's the £65!?!?!?!?!? New part. Think Ill go and pick it up from CC, can't face their p&p on top of that!!! (Original is only 20 months / 11k miles old). Thanks all. Link to comment Share on other sites More sharing options...
myothercarsa2cv Posted March 18, 2014 Share Posted March 18, 2014 This is the speedo drive wotsit: here It's what I have on my car, works well, and I believe the speedo gauges are the same in my car as they would be in a Sigma/Duratec car, so it shouldn't be a million miles out... Link to comment Share on other sites More sharing options...
Peter W Posted March 18, 2014 Share Posted March 18, 2014 Garry7, Interesting. My speedo went hay-wire last autumn (2007 roadsport 150 sigma). I rang Caterham and they said I should check the gap. When I pointed out the sensor was rock solid and clearly hadn't moved they still suggested I check it . Having seen your thread I'll have another a rummage around underneath and see if I can see the LED. I would rather it;'s an obvious sensor problem (despite the cost) rather than a hunt for a broken wire somewhere. I'll keep you posted. Peter Link to comment Share on other sites More sharing options...
michaeljclark Posted March 18, 2014 Share Posted March 18, 2014 Quoting sambler: Speedo used to fluctuate and then go to zero above 50/60mph. It would then recover as speed dropped and continue to fluctuate. Precisely what mine did on the Blat up to the 2012 IOM trip, prior to: Quoting SM25T: .... cable tied to the chassis tubes ... chafed through ...... and ended up immobilising the car too. Yep, blew the instrument cluster fuse, which caused the ECU to freak out as it couldn't see the instruments and it shut down the fuel pump. On the plus side, once it had been taken care of by a member of this parish on the IOM , we were back in action! And further fiddling by SM25T and others found more speed 😬 Mike Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted March 18, 2014 Share Posted March 18, 2014 Throttle butterfly opening fully at last was a great upgrade Link to comment Share on other sites More sharing options...
swsambler Posted March 18, 2014 Share Posted March 18, 2014 In response to your question....no apparent damage on old unit and green sensor working fine. Can only assume some signal breakdown in or from the old unit. Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 Update: Bought new sender - very reasonable £62 Finally got around to fitting it today, gap set to 1mm, set off on test drive in eager anticipation and...................nothing, not a sausage Back to garage, scratch head, jack up car, remove wheel, scratch head again. I opened up the gap to 2mm, put it all back together and it all works perfectly Very happy me! Thanks for all the pointers guys, got there in the end 😶🌫️ Edited by - Garry7 on 15 Apr 2014 18:36:02 Link to comment Share on other sites More sharing options...
John Vine Posted April 15, 2014 Share Posted April 15, 2014 Good news -- well done! Out of interest, when you set the gap (1 or 2mm), did you do the LED test? JV Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted April 15, 2014 Author Leadership Team Share Posted April 15, 2014 Hi John, I did try, but working outside the lock up, car on stands, I couldn't get my head at anywhere near an angle that would let me see the sensor head (hopefully I have understood what I was trying to achieve?). I'd love to know how I should have done it, just happy it's working again, was getting me down. 😬 Link to comment Share on other sites More sharing options...
Peter W Posted May 5, 2014 Share Posted May 5, 2014 ....................and the end to my own story. Having swapped the sensor for a new one and played around with the gap no joy. On closer inspection I found that the LED was working on the old sensor, simply by turning the wheel by hand - it flashes . So spoke with CC who suggested the only other option was a new speedo. So it was agreed they will send me one, and I can return it if that doesn't work. Guess what - it worked . When I suggested that a speedometer unit should not really fail after 5 years, 25,000 miles that fell on stony ground! They have said if I send the new one back they can send it away to have the old mileage put on it. Anyone know if I can do that - or is it best to let CC? Anyone need a spare new sensor let me know . Peter W Link to comment Share on other sites More sharing options...
John Vine Posted May 5, 2014 Share Posted May 5, 2014 Good news, Peter. It does seem that these programmable speedos are less than robust. After I'd spent many frustrating hours attemping to solve my speedo problems, the answer proved to be....a new speedo. James G sent me one to try, and it's worked perfectly ever since. He even arranged for Caerbont to change the black dial for a silver one. JV Link to comment Share on other sites More sharing options...
Peter W Posted May 6, 2014 Share Posted May 6, 2014 John, I think I will probably return mine as well to get the mileage set correctly and avoid confusion with MoTs etc etc. Onwards and upwards ! Peter Link to comment Share on other sites More sharing options...
John Vine Posted May 9, 2014 Share Posted May 9, 2014 I didn't bother getting my mileage corrected (two replacement speedos). I just made a note in the service record. JV Link to comment Share on other sites More sharing options...
Guest Posted May 17, 2014 Share Posted May 17, 2014 After a lovely first day blast yesterday it appears I have a dodgy / broken sensor or speedo. When I first put the sensor on the bracket (when building the car) I got no speed reading. Just before the IVA I adjusted the gap from about 1mm to 2mm and on the way to the IVA I was topping out at 60MPH on the speedo and then it just bounced. When I got my plates yesterday I adjusted the gap back to 1mm. The car would read up to ~30MPH then drop to zero. This morning I was all geared up to set the gap at 1.5mm (see my thinking there), and head off for a drive. However when I put the keys in and caressed the fob, nothing. The speedo didn't light up as normal and the fuel pump didn't kick in. Thanks to this thread and blatchat I knew to check the fuses and low and behold the 7.5A fuse had blown. I replaced it with the ignition off but when I turned the ignition on it blew straight away. I took the wheel of and took the tape of the sensor connector and disconnected the sensor from the wiring loom. With a new fuse in place the caressing of the fob bought the car to life. I put a multimeter (a what!), set to continuity, across the pins of the sensor and had short circuits between all combinations of all three pins. I am deducing that I need a new sensor. Fortunately I am still under warranty so I will phone Caterham on Monday and sort out a replacement. One thing that seems odd is how the cable and connector end of the sensor face the water spray. The unit seems destined to fail. I think when I get the new one I will put a ball of silicone on the end to stop any debris or water getting in. Any other thoughts appreciated. I still made it out for a blast just covered no miles and didn't know what speed I was doing. Edited to say there is no obvious damage to the cable or socket. Edited by - AndrewB on 17 May 2014 13:02:40 Link to comment Share on other sites More sharing options...
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