Me and Caterham speed sensors don’t seem to get on. One of my memories from my first Caterham was dragging a right-angle speedo drive down the M1 on the way to a track day. My 360R failed it’s first IVA because the speed sensor (old design) didn’t read over 50mph, and finally I dragged that sensor round the track for a whole session. Therefore a replacement was needed for the 360R, and I was sent the new 2018 design.

I have to say the 2018 design is the most stable speedometer I have ever had in a Caterham, the speedometer is like any other production car, so I was happy with the change. Unfortunately the new and old manual (2015c, v1.2 and v2.0) still reference the old design speed sensor, and neither reference the speed sensor earth modification, which was supplied with my kit.

I started the install by removing one of the small nuts, and winding the other to the end of the sensor. Then I screwed the sensor into the plastic “top hat”.

Without the locking nut I pushed the sensor into the bracket and measured the gap. This sensor needs to be a lot closer to the sensor wheel on the drive shaft, compared to the old sensor. My 360R worked perfectly at 0.025” or 0.635mm gap between the sensor and a sensor wheel high point. Therefore that’s what I set my sensor to for this build; to do this I used a feeler gauge.

Once set, I fitted the locking nuts on the top hat and the sensor. Remember, it’s only plastic, so no need to get all gorilla on the torque. Once it was tight I double-checked the gaps.

Once the electrics are all connected you can check the sensor is working: it lights up where the wire exits the sensor. It should light up for each tooth, and go out for all the gaps. It’s worth checking this carefully when you have power to the speed sensor.

UPDATE – I have now tested my speed sensor

A little heat shrink to cover the labels and protect the wire

I didn’t want to remove the labels applied by Caterham, just in case they are needed for warranty purposes, but I also didn’t want to have them on display on my radius arm, so I covered them in heat shrink tubing.

If you research the Caterham speed sensor, you will read about the earth mod. It’s about improving the earth for the speed sensor, instead of using the earth in the wiring loom. The needle can fluctuate and the speed reading can therefore be unstable as the speed increases, and this symptom is cured with the earth mod.

It‘s done with a small piece of wire that is connected to the chassis, local to the speed sensor. To do this, I removed the loom earth wire from the connector, and because I didn’t want to cut it out of the loom, I bent it back and covered it in heat shrink tubing. Next I inserted the earth mod wire and reassembled the connector.

I didn’t want to drill an additional hole into the chassis for this earth mod, so I fitted a slightly larger ring connector and earthed it under the mounting bolt for the rear anti roll bar. This is what I did with my 360R and proved it provided a good clean signal (I tested it with an oscilloscope), but I will check the earth is good when the electrics are connected.

The build manual (v1.2 and v2.0) calls for a hole to be drilled and a pop rivet fitted to hold a cable tie base. I think I would have used that approach if I hadn’t got carbon fibre interior panels. Instead, I decided to use a self-adhesive cable tie base.

The final part of the process was to connect the Econoseal connector and tie-wrap the wires. I removed the original tie wraps and reused the location to tidy the wires. It’s important to route the wires so they don’t touch any moving suspension parts, and to ensure that the speed sensor wire has enough slack to move with the suspension.

Tools Used

  • Heat gun
  • Soldering iron
  • Side cutters
  • Pick
  • Feeler gauge
  • 17mm open ended spanner (x2)
  • 8mm open ended spanner (x2)