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Wheel Speed sensor / sender

Updated: Jan 21, 2019

A couple of days ago I fitted the speed sensor, however, I found myself short of a couple of key components, and so concluded I'll blog the install immediately. The components aren't detailed anywhere, I hope this blog helps as an easy reference to future builders.

Since the speed sensor is fitted at the rear of the car, on the driverside rear ARB bracket, it's sensible to assume the installation of the DeDion bar, Ears, drive shafts and so forth need to be completed first. I'll blog those items when I have time, but I anticipate sizable blog articles hence the delay.

The speed sensor is shipped in a sealed packet as shown below.

Caterham 7 S3 420R Wheel Speed sensor
Caterham 7 S3 420R Wheel Speed sensor

A close of the threaded sensor section.

Caterham 7 S3 420R Wheel Speed sensor
Sensor section, threaded.

The threaded sensor mounts through the rear anti-roll bar bracket which should now be attached to the back of the ears and rear anti-roll bar as illustrated in the following image. The bracket has two holes, well mine did, one which is larger than the other.

Caterham 7 S3 420R ARB bracket
Rear ARB bracket (driver's side) showing two holes for the speed sensor

The manual clearly states to install the sensor so that it is between 0.8mm and 1mm of the serrated disc fitted to the drive shaft. It quickly became apparent that my sensor would pass through the larger hole and use of the smaller hole would prohibit such proximity with the serrated disc. Something isn't right.

Caterham 7 S3 420R ARB bracket
Plan view, showing alignment of holes with serrated disc fitted to the drive shaft.

After chatting on BlatChat and speaking with Derek @ CC it became apparent I needed another part, a "top hat".

Caterham 7 wheel speed sensor adapter
Top hat, or adapter

I think that is a fancy name for what is essentially a sizing adapter. The top hat has threads on the inside and also on the outside too. You basically thread the sensor into the top hat, pretty much all the way through, this converts the thread diameter to that of the larger hole, and thus solves the problem of the proximity to the serrated disc.

Caterham 7 S3 420R wheel speed sensor
Sensor fitted within top hot along with relevant securing nuts and washers

The instructions are a little ambiguous with respect to the locking nuts, I opted to follow advice from Blatchat and fit the locking washer and plain nut on the side nearest the serrated edge. There is only one locking washer supplied and capacity to fit a second does look a little low.

I've yet to sort the cable out, that is a task for another day. As always I hope you found the post helpful and informative.

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