mossy7 Posted January 5, 2017 Share Posted January 5, 2017 So, I'm out in the 7 today, ( bright, bit damp, cold but oh so much fun)when the speedo starts doing an impression of a mad thing, bouncing all over the place.Up to about 60mph all seems fine. Much over that and it starts bouncing from 140 to 0 and all points in between. Slow down and it settles back to normality. The private road was quite smooth too. Any one got any suggestions? ( Sigma 140, with a 5 speed box, Mazda MX5 I'm told) Link to comment Share on other sites More sharing options...
JNC Posted January 5, 2017 Share Posted January 5, 2017 Either an earth fault or sensor failure. There's a lot about this on here Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 5, 2017 Member Share Posted January 5, 2017 John's probably right, but that fault could also be in the instrument. Can you find the sensor at the wheel or at the gearbox?After that the solution is probably in the archives (as this is all too common). For wheel sensors there's a procedure for testing and adjustment. There's a factory Workshop Notice to improve the wiring. All other instruments behaving normally?Happy New YearJonathan Link to comment Share on other sites More sharing options...
mossy7 Posted January 5, 2017 Author Share Posted January 5, 2017 Happy new year to you too Jonathan,all other instruments are fine..I just have no idea how fast I'm going! Link to comment Share on other sites More sharing options...
John Vine Posted January 5, 2017 Share Posted January 5, 2017 Have a read of this thread and this thread.Your symptoms are likely to be due to one of these: Incorrect sensor air gap Electrical interference in the loom Faulty sensorThe first two are dealt with in detail in the above threads.JV Link to comment Share on other sites More sharing options...
ChrisC Posted January 5, 2017 Share Posted January 5, 2017 Looking at the way my sensor wiring was rerouted for the IVA test (next week) during the Post Build Check, it puts a lot of load on the wire joint between the sensor which is unsupported. No wonder this leads the sensor failure. Post IVA I am going to give this wire a little thought. Link to comment Share on other sites More sharing options...
John Vine Posted January 5, 2017 Share Posted January 5, 2017 That's interesting. This is how I set mine up during the build:The wire forms a loop, and is tied to the lower chassis rail.Is yours like that? Can you post a photo of the wire routing?JV Link to comment Share on other sites More sharing options...
JNC Posted January 5, 2017 Share Posted January 5, 2017 Tip, being as your dealing with an electronic sensor don't touch it with bare hands use rubber gloves to prevent damage . Link to comment Share on other sites More sharing options...
Bricol Posted January 5, 2017 Share Posted January 5, 2017 If that sensor can't deal with bare hands, it's not going to last long on a car!Can't quite see, but if the cable at the sensor end is straight out of the sensor, relying on it's cable relief gland etc, I've be tempted to secure the cable to the upright,then do as you have, a loop back to the chassis. I might be tempted to take it to the centre of the de-dion too, to minimise the about of movement - that wheel end will be moving a lot, more than full on bump of both wheels.Dealing with vibration issues on a number of machines over in the USA at the moment - cable support fails, moisture ingress, servo motor fails! Link to comment Share on other sites More sharing options...
John Vine Posted January 5, 2017 Share Posted January 5, 2017 From CC's online store (but doesn't show the cable exit):JV Link to comment Share on other sites More sharing options...
OliverSedlacek Posted January 5, 2017 Share Posted January 5, 2017 Why should you use rubber gloves when dealing with sensors? If you're worried about electrostatic discharge, get a pukka earthing strap. Link to comment Share on other sites More sharing options...
JNC Posted January 5, 2017 Share Posted January 5, 2017 How many people have a pukka pukka earth strap !! Or a pair of throw away gloves ? If the sensor is delivered in a fancy anti static bag it's worth treating it properly . Perhaps that's why the high failure rate ? Link to comment Share on other sites More sharing options...
John Vine Posted January 6, 2017 Share Posted January 6, 2017 If the sensor is delivered in a fancy anti static bag it's worth treating it properly . Perhaps that's why the high failure rate ?That's a very interesting point. AIUI, electrostatic discharge (ESD) is certainly not good for the type of transistor in a Hall-effect sensor. But it's a while since I fitted my sensor, and I can't recall whether CC sent it in an anti-static bag, Also, I've read that ESD damage can sometimes take months to appear as an observable problem. What's the best way to counteract it when handling this sensor? Do you simply short the leads together, and earth yourself when handling it? The Assembly Guide doesn't mention this at all.JV Link to comment Share on other sites More sharing options...
ChrisC Posted January 6, 2017 Share Posted January 6, 2017 This is how mine was, the PBC re located the connector to the loom. My concern is where the wire enters the sensor, its just looks like a wire held with epoxy. The sensor is moving with the suspension and the unsupported wire is free to move where it likes, which makes me think its likely to break where the wire enters the sensor. I think given the design it is inevitable that the sensor wire will break, its just a shame the break will happen close to the sensor making repair virtually impossible. I would like to see the sensor moved to the inner CV joint near the handbrake cable adjuster, that way its less exposed to the elements and not moving with the suspension travel, but given that is a little extreme for my modification skills. The option that is running through my mind it a connector closer to the sensor, attached to anti roll bar bracket, so the sensor its wire and connector all remain stationary in comparison to the suspension travel. A second sacrificial wiring loom for the three wires is created with a connector each end, one for the now secured sensor connector and one for the secured main loom on the chassis. This would at least make the inevitable failure cheaper. Link to comment Share on other sites More sharing options...
SteG Posted January 6, 2017 Share Posted January 6, 2017 It will most likely be the sensor (Approx. £70)or the air gap requires adjusting. Had the same fault last summer. Presuming yours is not very old so it will have the earth mod already done. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 6, 2017 Member Share Posted January 6, 2017 This would at least make the inevitable failure cheaper.Nice design principle. :-)I hate wiring lamps on bikes because of the inevitable fudge around the headset. But at least wireless speedometers are now available, cheap, reliable and fudge-free. Anyone fancy sketching out how that approach would handle the suspension movement? With as few batteries as possible. With suggested parts? Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted January 6, 2017 Share Posted January 6, 2017 ...a connector closer to the sensor, attached to anti roll bar bracket, so the sensor its wire and connector all remain stationary in comparison to the suspension travel. A second sacrificial wiring loom for the three wires is created with a connector each end, one for the now secured sensor connector and one for the secured main loom on the chassis. That's a neat idea. And if you made the second loom from silicone-sheathed cabling (like the race TPS sub-loom or flexi-coil sub-loom), it would be ultra flexible and very tough. Even though I've never had a fracture in the sensor wiring in 40K miles, I think I might just explore your idea anyway.JV Link to comment Share on other sites More sharing options...
Stuart7 Posted January 6, 2017 Share Posted January 6, 2017 Both my 7s had this problem, both fixed by adjusting the air gap (see link above). The gap needs to be bigger than you might expect, so start off by increasing it a bit and see if that makes an improvement. Link to comment Share on other sites More sharing options...
Area Representative Geoff Brown Posted January 6, 2017 Area Representative Share Posted January 6, 2017 Incorrect air gap (should be 1mm) & an excessive build up of crud in the exciter teeth on the drive shaft are the big problem. Though there are posts about the poor earth circuit for the sensor which affects some cars. But for some reason not all?The other problem is the strain on the potting at the entry point of the loom into the sensor. A loop in the loom before attachment to the chassis relieves the strain. But that solution may be too late.As to static...mmmm. After replacing the BMW Diff output seals the sensor was refitted with clean hands, albeit with that film of grease one cannot get rid of. Gap set & test drive results OK. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 7, 2017 Member Share Posted January 7, 2017 ...a connector closer to the sensor, attached to anti roll bar bracket, so the sensor its wire and connector all remain stationary in comparison to the suspension travel. A second sacrificial wiring loom for the three wires is created with a connector each end, one for the now secured sensor connector and one for the secured main loom on the chassis. ...That's a neat idea. And if you made the second loom from silicone-sheathed cabling (like the race TPS sub-loom or flexi-coil sub-loom), it would be ultra flexible and very tough. Even though I've never had a fracture in the sensor wiring in 40K miles, I think I might just explore your idea anyway....Might be easier than wireless!Would that use the existing connectors for the extension or replace them? Do we know the type of connectors?Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted January 7, 2017 Share Posted January 7, 2017 Would that use the existing connectors for the extension or replace them?I think ChrisC's idea is to knock up an insert sub-loom, using the existing male/female connectors -- rather along the lines of CC's loom for their high-level brake light. Do we know the type of connectors?On my car, they are 3-way Econoseal ESC3F and ESC3M.JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 7, 2017 Member Share Posted January 7, 2017 Thanks: it's good to have that documented.Jonathan Link to comment Share on other sites More sharing options...
Area Representative Kingsley Young Posted January 7, 2017 Area Representative Share Posted January 7, 2017 I had a very similar problem earlier this year, I had the sensor readjusted on the rear hub and it has been fine ever since. May be as simple as that. Link to comment Share on other sites More sharing options...
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