Talk Morgan Forums Thread Like Summary - M3W Speed Sensor E340022 Discontinued

I recently found out that MMC appear to have discontinued the speed sensor that is fitted to the M3W (5-Speeder) and +4 Duratec.



On the M3W, this sensor is fitted through the right hand front brake calliper bracket. As the hub rotates, five bolt heads pass closely by the head of the sensor, thus creating 5 pulses per rotation and this signal is subsequently converted into the speedo reading.

MMC have superseded the sensor with this type:



It’s MMC part number E221002 and as you can see it is quite different to the original one, having an integral socket. To compound the problem, the original loom connector needs replacing as it isn’t compatible with the new sensor.

I therefore set about making a replica of the original type. This has a 5 Inch (125mm) lead leading to an Econoseal plug, with a ‘pull-up’ resistor between the sensor output signal and +5V.



Once I had sourced the components and the special crimping tool needed for the connector pins, I assembled the assembly with a suitable amount of heat-shrink sleeving to make it as waterproof as possible. I have to say that it was a bit of a fiddle, especially having to incorporate the resistor into the plug.

I’ve often thought that having the sensor connector adjacent to the lower wishbone where it is guaranteed to be exposed to copious amount of water and muck from the road is not one of Morgan’s most inspired decisions (and doesn’t look particularly attractive either). Indeed, when I took my original connector apart, there was evidence of corrosion on the pins, even though the connectors are nominally waterproof.

Therefore, I am also making up a long-lead version of the speed sensor which has a 1 Metre lead. Once the existing loom has been unclipped from the lower wishbone, it can be fed back up to the area below / in front of the oil tank, adjacent to the red +12V post. The lead from the ‘long’ sensor is then run along the lower wishbone and fed up behind the chassis tubes to the new connector position. The plug, socket and ‘spare’ cable can then be tucked under the transverse chassis tube and held in place with a couple of tie-wraps. Obviously, this is a bit more involved to fit but does result in a much neater installation and a more appropriate position for the electrical connector.

When I removed the original sensor from my car, there were witness marks on the sensor head where it had come into contact with one or more of the hub bolts.



The sensor spec calls for a clearance of 0.3 – 2.3mm between the sensor and trigger so I sourced a 1mm thick shim washer which can be fitted between the sensor mounting flange and the brake calliper bracket to increase the clearance if necessary.

The original sensor retaining screw is a button-head type, needing a 5mm hex key to release. Mine was quite corroded so I replaced it with a stainless steel cap-head type requiring a 6mm hex key. This should make it easier to remove in the future if it ever needs to be replaced again.

This is the 'short-lead' kit:



The ‘long -lead’ kit is similar. However, in order to release the loom from the lower wishbone, three P-clips need to be removed. Therefore, this kit also includes 3 replacement black pop rivets for reattaching those clips as well as some tie-wraps to finish off the installation.

If anyone is interested in one or other of these sensors then please PM me as I’m going into limited production! These are listed in the ‘For Sale & Wanted’ forum HERE.

Seeing as we’re pretty much house-bound at the moment and there’s nothing on the telly, I decided to let my mind wander a bit regarding why MMC might have deleted the pull-up resistor from the M3W speed sensor.
The speed sensor used (Honeywell 1GT101) is primarily designed as a gear tooth sensor.

In this application the triggering frequency will be much higher than in the M3W. Indeed, the sensor is specified to go up to 10kHz, i.e. 10,000 triggerings per second!
A back of the envelope calculation indicates that, even at 110 miles per hour, the speed sensor will only be working at 111Hz, i.e. 111 times per second. (It is linear, so at 80mph there are roughly 81 sensor pulses per second.)
The purpose of a pull-up resistor is to ‘reset’ the sensor output between pulses. This is probably desirable at 10kHz but not really necessary at 111Hz.
In addition, omitting the resistor will have simplified the production of the sensor assembly by MMC’s supplier which may have saved a few pennies.
All just my ramblings of course but I have verified that the speedo works fine on my car with or without the pull-up resistor. Therefore, I plan to omit the resistor from future ‘Bunny’ speed sensor assemblies I make.
Right, everyone can wake up now!

I have fitted the first "customer trial fit" version of the, "Bunny Wheel Speed Sensor" and it all works perfectly. I had not had a problem with the wheel speed sensor in my 11 years of ownership but on taking it apart to fit the new sensor I found the connecting Econoseal plug was not as waterproof as it should be and the pins were a bit corroded, I may have been on borrowed time! I also found that the clearance to the trigger bolt tails was nil and the sensor had some score marks, the spacer washer supplied with the new sensor fixed this.

Replacement was simple with the connecting plug now located near the battery post and clipped to the chassis tube, well out of the way of any water. This is a worthwhile modification and certainly worth doing if you have any speedo problems, they are usually related to the connecting plug. The wheel speed sensor does speedo indications but also has inputs to the indicators and engine idle speed mapping, so an important sensor that will cause issues if not working correctly.

Quite why MMC would market a replacement item that doesn't fit or work.......

Hi Bunny - my March 2020 build M3W appears to have the E221002 variant. (It was one of the last cars built before the Covid shutdown)
Here's a picture:

HI Andy
Mine is from May 2012 although the VIN has a 'B' letter which means : 2011.
So it is probably registered by MMC already in 2011.
I just checked for you and the bolt is a 6mm
regards