Speedometer Stopped Working

[BrianD]

Out for a run yesterday, the speedo started jumping about and then dropped to zero, never to move again! Is this a common problem? Any ideas what I need to look for as I've no idea how it works!!

Brian,  2014 420R

[John Vine]

Sounds like the sensor air-gap could be out. 

For info on how to adjust, see Part B of this Guide.

JV

[Saltyhair81]

Mine did exactly the same and turned out to be the wheel speed sensor. Would bounce around and then completely die. Mine was done under warranty but I've been told it can be a bit of a tricky job. Hope that helps 

[ScottR400D]

Is actually quite an easy job, just a little tricky to get the gap right. If its been working fine and just suddenly stopped, not to work again, it may be the sensor has failed. It's a Schneider XS108B3NAL2, available for about £40 from various places, £56 from CC but they do supply it with a loom connector so not too bad.

I recently took mine off, doing some other work. It had worked faultlessly up to an indicated 130mph up to then, for about 4 years. I didn't note the gap.

I put it back with a gap of 1.2mm. It started to swing at about 85, stopped altogether by 90 but started again on slowing below 85.

I adjusted to 1.0mm. It started to swing at about 50, stopped altogether by 55 but started again on slowing below 50.

It's now at 1.45mm and is steady to 80 or so, haven't been able to go faster yet.

I noticed, turning the hub at a 1.00mm gap that the indicator light on the sensor is near enough permanently lit. It seems the hysteresis in the switch means that if the gap is too low it picks up the next tooth before it's 'lost' the last one, so there's no count takes place and the speedo stops. So the narrower the gap, the lower the speed at which it stops. Within reason, of course, if you go too big it won't pick up the signal fast enough, though the sensor is rated at a nominal 2.5mm sensing gap. 

Be careful not to over tighten the nuts, the sensors aren't hard to break.

 

[ChrisC]

I wouldn't replace the sensor like for like. The sensor Caterham introduced in 2018 as a replacement is much better at doing the job, is more stable and cheaper as well.  Obviously you could source this elsewhere, but you would need someone to modify your bracket or make a mounting boss, so hence it might be cheaper and easier to just order from Caterham.  
The post 2018 sensor has a much smaller air gap, .625mm works perfectly.

[ScottR400D]

The older version was never unstable, once the loom issues were resolved, it just needs setting up properly in the first place. 

[ChrisC]

Scott have you used a new one?

[ScottR400D]

No. The one I have had always worked perfectly once set up to the right gap. Why would I need a new one? 

[ScottR400D]

No. The one I have has always worked perfectly once set up to the right gap. Why would I need a new one?

[ChrisC]

Only to replace a faulty one, which is what I did.   There is a difference between the reading they generate, but I can't describe it. All I can say is when I changed the speedo was strange, sort of tin top like.  

[John Vine]

Re #6:

The older version was never unstable, once the loom issues were resolved, it just needs setting up properly in the first place. 

That's exactly my experience too.  I suffered endless problems with my speedo (2008, programmable) in the early days.  It would either stop working completely after 50 miles or so, or the needle would bounce around, and even dip in time with the indicators or brake lights.

The solution was the earth mod described in WN572.  Once I'd applied that and set the gap correctly, the speedo worked flawlessly, and has done for the last 5+ years.

JV

[Nillbymouth]

BrianD - Has started working again? John Vine in the previous post could be correct with the Earth Mod being required. My 2014 Supersport speedo does the same but only on hot days. It then works flawlessly until the next hot day. I've got the stuff for the earth mod but have yet to fit it.

Before you buy a new sensor it might be worth checking to see if it has started working again

[Alan Reeves]

The money is firmly on John V

[Geoff Brown]

The pre 2018 sensors can be fragile/unreliable.

Way back in 2016 & as part of the diff output seals job I removed the sensor it was bagged & tied it up well out of the way. A subsequent road test after the job had the speedo exhibiting all the usual nonsense until it stopped altogether.

No amount of adjustment helped. Opted for a new sensor with belt & braces earth mod. Everything OK since. But when blatting in the previous very hot weather the speedo needle had an occasional small jump up in the 70 - 90 area but OK now the ambient temp has dropped.

Original style sensor also not tolerant of 'high' temps'?

[John Vine]

Opted for a new sensor with belt & braces earth mod. Everything OK since.

But which of those was the actual fix, Geoff?

Original style sensor also not tolerant of 'high' temps'?

That's possible, I imagine, but my original-style sensor happily withstood temps of 30-35C while touring France last year -- and a lot better than I did!

JV

[Nillbymouth]

An update to my previous post since there is now a new thread on speedo issues.

I installed the Earth mod and it made no difference to me. I then measured the gap for the sensor and it was only 0.78mm. The LED flashed so suggested it worked at this gap. I increased the gap to 1.07mm and the speedo is working all the time.