toothed wheel - what is it for?

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John Vine
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I don't think so.  The shafts are custom-made for CC.  I think the reluctor ring is as well, as they seem to be unobtainable on the open market.

JV

Beagler
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Found this,

ABS (reluctor) ring

ABS rings fit on each wheel, working with sensors to send wheel-speed data to the Anti-lock Braking System controller. Using this data, the ABS controller stops the wheels from locking up by ensuring each one stays in sync. It does this by applying hydraulic pressure at just the right time. A faulty ABS ring will cause a warning signal to light up on your dashboard. When this happens you must replace the faulty ring immediately. Without vital data from the ABS rings and their sensors, the controller won’t do its job properly and your car will become unsafe to drive.

2019 270S 1.6

John Vine
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Well yes, that's certainly what ABS reluctor rings do.  Indeed, the ring on our driveshafts may well have started life as an ABS ring from another application.  The snag is that its identity and source is a closely-guarded CC secret! 

Several of us have tried to find out whether there are other suitable 43-tooth rings around, but without success (AFAIK).  An early candidate was this Rover/MG one, but it seems to have too large an I/D.

If anyone does know the identity and source of these rings, please tell us.  And if anyone has an accurate measurement for the O/D of the driveshaft tripod-housing ("tulip"), that would be good to know too. 

JV

timb2117
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 Hi John this is the old speedo with reference number, the new one caerbont are supplying is ees3-1b32-17b

Yes the link to CC website was accurate you are correct that right hand gearbox sender which (as it becomes electrical after the right hand - must have 12v supply - I think)

Car was an 05, K series 1800cc VVC roadsport SV, supplied in a box to caterham cars australia pty ltd and assembled by them.

I will have to jack up the car and check the rear led - after just taking the gearbox and engine out and replacing them I am sort of over things at moment and just trying to do my online research prior to the last leg of fixing the dratted speedo.

Oh and dont even start me on the reverse light switch that I very neatly sheared the two diddy brass connectors on and am waiting for that in post too :)

Many many thanks for the direction and advice I will take it all into account and my membership fees to this great club will never be overdue!

Jonathan Kay
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If it does come back to working on the gearbox sender you can increase the lateral clearance by slackening the gearbox mount (and possibly engine mounts) and shoving.

Jonathan

John Vine
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Re #15:

That speedo looks like the version before the electronic programmable one.  To confirm this, check whether there's a set of four dipswitches under the big black grommet.   I take it it has a KPH display?

EES3-1B32-17B is definitely the electronic programmable "stepper motor" version (this one, I think), driven by a driveshaft reluctor ring and sender.  The next step is to check whether your existing driveshaft sender has a 12v supply.

JV

 

timb2117
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This is the sucker... confirmed it does have a 12v supply when ignition on. 3 wires leave the actual sensor - blue /brown/ black. There is no visible LED - would they have used LED 16 years ago? They join into 3 loom wires coloured I think - white/ black and purple / Black and green. I've scrutinized the build manual to no avail.

Was considering (neanderthal) disconnect it take it for a drive if alls well then consider finding the place near the cockpit where these wires are and simply wire them to the new speedo?

Does seem very weird though to have gone to trouble of putting it there WITH voltage then not using it for anything......

ScottR400D
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The LED can be hard to see if it's not lit and it may not be if the gap is too big. 

I've been thinking about what else that could be doing and all I can say is that if mine is not set correctly the only thing affected is the speedo. I can't think what else it would be needed for though I stand to be corrected. 

I would suggest that you check the gap and see if you can get a response, then search for the correct feed to the speedo or run a new one. 

John Vine
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Re #18:

That sounds very promising.  The LED sits at the cable end of the sensor:

With the ignition on, it lights up as each tooth of the reluctor ring passes by the sensor.  But as ScottR400D points out, if the air gap is wrong it may not light up at all.   I suggest you set the gap at 1mm and go from there.  More info here.  And I'd agree that the sensor is unlikely to do anything other than feed the speedo.

This is the connector wiring:

Note that the sensor black wire is not, as you might expect, the earth but rather the pulse wire.

The Assembly Guide shows this for the loom connector:

What connector do you have at the speedo?  This thread may help re pin-outs and the possible need for a pull-up resistor.  

I'm still puzzled why the builders opted for a gearbox-driven sender.  Maybe the speedo supplied in the kit was the older version, and fitting the matching sender was the easier solution?  Of course, your car dates from the time (2005?) of the speedo/sender changeover.

JV

aerobod
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The speed sensor may also connect to the ECU (Pin 27 on my car, which originally had the 992 ECU). Path is YB155 on sensor to pigtail of YB155, YB156 & YB157. YB157 connects to the speedo pull-up resistor (1KΩ), which then connects to YB178 on the speedo. YB156 connects to the engine harness on YB54, then on to Pin 27 on the ECU.

Although Caterham don't seem to use the road speed input for anything useful in normal car operation, with Easimap you can see the road speed as one of the channels that are logged, or in a pane on the Easimap dashboard.

James