Erratic speedo

[Jeff210R]

The speedo on my 2014 Supersport R 210 has started playing up suddenly.  Jumps around and then stops working completely; also the mileage has stopped recording.  But the LCD display is showing steady.  Anyone point me in the right direction?

Thanks. Jeff

[Jonathan Kay]

Which type is it... sender in the gearbox or sender on the rear axle?

Guide: "Speedometers"

Once we know which there's quite a lot of experience with what's likely to be the problem...

Jonathan

[Jeff210R]

It's on the rear axle Jonathan.  It seems to be "Where the speedo needle moves erratically, especially at high speeds, and sometime sits resolutely on zero for minutes at a time" so I've checked the light emissions as suggested and it seems to be pulsing for all the teeth so it looks like the air gap is correct?  Or should I check that it is 1mm?

[Jonathan Kay]

I'm not an expert on this, but while we're waiting...

... IIRC there have been reports of the light working when tested at rest but the speedometer becoming inaccurate at speed. So I'd set the gap as suggested.

Has any work been done recently in that area or near the wiring?

Jonathan

[Jeff210R]

Yeah I think I'll give it a try. Might have been disturbed when new LSD fitted.

 

[ScottR400D]

JK is right, you can get the lights flashing turning by hand but the needle will be bouncing about all over the place. 

On occasion, when I've had mine disconnected and replaced I've had it not work at all or drop out at 40+, 80+ or even higher. 

It's all to do with getting the right gap and it's not always 1mm. The last time I adjusted mine I started at 0.8 and worked out a tiny bit at a time till it functioned properly at 1.1mm. (certainly up to 95/100mph or so, haven't been  be any faster.)

It's tedious having to jack up and remove the wheel each time but you should get it in two or three goes.

The other thing I would mention is that mine has at times worked perfectly at 0.8, then at others it's needed up to 1.1, as I said. No idea why it should change.  

[Jeff210R]

At least it's relatively accessible!

[andy_harries]

Mine is erratic and stops working over around 80mph, but as I only do that speed on track and I tend to watch the shift lights to think about what I'm doing rather than the speedo I can't be bothered to fix it.

Have fiddled with the gap in the past to get it working fine at normal road speeds - gap is 1mm - and when turning it by hand there don't seem to be any issues with the light.

[Geoff Brown]

The gap does vary around 1mm +/- fractionally. After fitting diff post Tracsport I set the sensor to a very tight 1mm. It worked. Unlike other attempts when the speedo needle had a life of its own. Out a bit in a bit 

[Jonathan Kay]

Very interesting.

The Guide has sections on "Adjusting the Air Gap" and "Eliminating the Interference".

Jonathan

[ScottR400D]

JK, having read the bit about adjusting the air gap I would say that I've done all that and had every tooth give a flash but then still had it drop out on the road. 

I assumed that if it's too close, the light will come on when being turned by hand but at speed the sensor is too close to read the 'gap'. I came to the conclusion that it was quicker to start tight, test and back off till it works at all speeds. 

I believe the later sensor is a lot more consistent, ChrisC has commented on it before now. 

[Nillbymouth]

I had similar problems when the outside temperature was above approx 22C. Below that temperature it worked faultlessly. Checking the sensor and it flashed perfectly. When I measured the gap it was 0.78mm. I moved it out a little and now the gap is 1.07mm and I've had no problem

[ChrisC]

You are 100% correct, the new sensor (cheaper than the old) is some how not Caterhamish, unlike the original electronic sensor.  It works regardless of speed and temperature, gives a consistent reading just like every other product car.   

Obviously the introduction of this more reliable speed sensor also coincided with a new problem where the trigger wheel moved on the drive shaft, so the balance in the universe was restored and Caterham would once again have unreliable speed readings. Fingers crossed my 2019 kit supplied car hasn't suffered this.

Oh and the new sensor likes to be a lot closer to the trigger wheel. 

[Jeff210R]

Well folks. I checked the gap and it was 1 mm and flashing fine. Nevertheless I reduced it to 0.9 mm by way of experiment. And it stopped flashing! Moved it back to 1 mm and it started flashing. The sensor had considerable free play in the mounting hole so I ensured it was central on the trigger wheel. Road tested and solid as a rock (although I only went up to 50). I note the above reference to temperature. Can't understand why something so simple to every other car on the road becomes complicated for Caterham? It's not exactly rocket science.

[ChrisC]

I had problems with the speed sensor during my first kits IVA.  It wouldn't read speeds above 50mph. Ultimately it was the reason for a fail, but I was given time to adjust it three times during the test.   I think there are a number of factors that are at play.

The first is CC selection of the sensor itself, the speedo is wired for a PNP sensor, but the sensor NPN.   This is why there is a resistor in the speed sensor circuit.  I can't remember if its NPN and should be PNP, or PNP and should be NPN, but either way the sensor isn't how the speedo is configured.  The resistor get hot when then the sensor is off, meaning every time you stop and you have the ignition on you have a hot resistor under the dashboard.  I also feel this sensor is more industrial use, not automotive, i.e. its not like any ABS sensor I have seen on any product car.

The sensor location,  I can never understand why the sensor is located on the outboard tripod joint, when it could be been located on the inboard joint, where it would have had more protection and the wiring would have been more static.  Obviously wiring damage due to fatigue wasn't my cars IVA problem, given all the components where new.

Signal interference.   After my IVA fail, I wanted to be 100% sure I didn't waste my time during the retest, so I investigated the signal quality from the speed sensor only to find interference on the speed signal coming from the ECU.   I suspect this is why CC choose to use the reverse NPN/PNP sensor as far a the speedo is concerned, so they can also feed the ECU.   However speed isn't used by the 992 MBE ECU fitted to an Oct 2015 supplied 360R kit.   I was able to clean the signal by isolating the speed sensor connection from the ECU connector, but this ultimately didn't result in any speedo improvement, so I reinstated it.

Earth mod, improved signal quality, and was my ultimately my solution to the IVA problems, but the signal was never "clean".  At that stage working was all I was looking for.  The IVA test is only up to 70mph, so it passed, but my cars speedo would always read 0 at speeds above 105mph.  This is a common problem, you can see it so many times on YouTube track day videos of cars of that age.  

Fast forward a year, and in 2017 at a track day my speedo started to get worse, and then stopped all together.  The reason was obvious after the session, the speed sensor had come loose and was dangling on the floor.   Obviously I hadn't included the speed sensor in my spanner checks, and given it's state I hardly felt a warranty claim was valid, so I purchased a "new" style speed sensor.   All I can say there is a obvious improvement it the quality of the speed reading (as stated above).  My observation about signal quality and wiring design may no difference to the new sensor, and I understand CC no longer recommend the earth mod.  There must be a spec change between the new sensor and the old sensor, and this is the reason for the improvement, and therefore the old sensor is working close to it limits hence all the problems. 

[Jeff210R]

Ye God's but Caterham do complicate things. Why cannot they just replicate the set-up used by somebody like Ford? After all it's not asking that much to have a working speedometer in the 21st century is it?! I suspect some people may find this attitude to a known problem a charming quirkiness but personally I think it is a sign of incompetence and indifference to real customer service.

[ScottR400D]

#15 Chris, you mention a resistor in the circuit. Do you remove that with the new sensor or does that issue remain?

 

 

[ChrisC]

The resistor remains with the new sensor.  Have to say that's one area of the current design I still don't like (that and the position of the sensor).  Apart from that it's nice to have a speedo that just does what a speedo should do.

[ScottR400D]

Thanks.