The speed sensor on my 2005 Roadster is on the gearbox output flange, so is quite difficult to access. At some point before 2012, it was moved to the right hand/offside stub axle.
This leads on from my Kingpin thread, but is worthy of its own thread. I removed the speed sensor from the stub axle when I replaced the bushes, because its a fragile looking item, and may have been damaged during that process. What I hadn't realised was the real fragility of this component. The unit is an 8mm fine thread stud which has been drilled down the centre, and what results is a very thin walled stud with limited strength. Inside is the electronics in a resin base. What happened when I refitted the stud, and 'nipped' the nut (and not very tight I might add) - was that the thread split and in doing so, cracked the resin inside and broke the circuit..............
This is how it goes together - the plug has three waterproof plugs in the end, and the cable runs through the cable protector shown here.
Ignore the blue blob on the end here. I was thinking about using that to set the gap but didn't use it in the end.
The obvious route to locate a new sensor was a Morgan Dealer, BUT - given my recent experience when I tried to get some brake pad pins and springs, the likely reaction would be that it would need a factory order and that would take time. My experience of factory orders in the past have been that you should expect a "number of weeks". This is something that both MMC and the dealers need to do something about, because the delays are not acceptable.
So a quick look on the internet revealed that the sensor is Revotec, and is available from a number of suppliers from stock. I placed an order with Demon Tweeks and received the sensor in three days. I also had to source a new weatherproof plug, as the original was in less than good condition. The sensor comes with two nuts, the idea being that it can be fitted on a bracket. I wondered why MMC had only used a nut on the outside and threaded the stub axle.........
You'll note from the instructions that a gap of no more than 2mm is required, so in order to establish how far to screw the sensor in I first took a thinner bolt and used the nut as a stop, pushed it through the hole and adjusted it until it just contacted the bolt heads.
The required length from the back of the stub axle is 18mm.
In order to give a 1mm gap, I set the nut at 17mm - so...
BUT, on refitting, I found the reason that MMC don't use a nut at the rear - the nut fouls the stub axle............
So I recalculated the gap from the outer edge of the stub axle, 9mm is required. I refitted the stud, and the outer nut was secured with Locktite.
Before doing that I had cut the cable to the right length and fitted the plug.
I also had to change the plug on the loom......
This is a waterproof plug with a tight sealing grommet in the end.
The loom colours are yellow; yellow/black trace; and green.
The sensor colours are brown; black; blue.
The matches are:
brown to green - 12v +ve fused switched supply
black to yellow - 12v -ve supply
blue to yellow/black - signal to instrument - white/black on speedo
The next job was to refit the hub, and by rotating the disc, that the sensor LED was flashing...........so generating a signal
I then put the wheel on temporarily, put a mirror & torch on the back of the seat, and checked the the speedo responded - it did! It was easiest to see with the garage lights off, and sidelamps on.
I could get enough momentum to be able to walk round and check that the speedo was working properly
All that was left to do was to shrink some wrap over the sensor end of the cable, and tie it up out of the way.
And then all that was left to do, was to replace the split pin in the hub, and refit the caliper and wheel. Job done!!!
