Seeing as the original Fairey overdrives are becoming harder to find (and parts even harder), Global Roamer's overdrive appeared to be the way to go.
Please note: the below are not intended to replace the instructions provided by Global Roamer! Their instructions should be obeyed to the letter. My entries here are partial, and just to illustrate my personal experience.
What do you get when the package arrives? This:
It weighs 45 lbs (20.5 kg). And inside, you'll find this:
The overdrive unit itself was larger than I though it would be. The book of cartoons is a nice touch. And after reading through the instructions, they are clearly written and well illustrated.
Installation of the Roamerdrive main unit was fairly straightforward. Here, a gold-coloured special socket (not included) is used to remove the castellated nut from the rear of the gear shaft. I tried to use a brass drift to get the nut to move, but no luck, and didn't want to hit the nut harder in case something broke.
The gears have to be immobilized to unscrew the castellated nut.
In this view, the castellated nut, locking plates and rear gear have been removed.
One of the first things to do on the Roamerdrive unit is to remove the black hex nut that lies inside the coupling. In order to remove this, the three set screws in the outer surface of the coupling have to be loosened first.
Black hex nut inside the coupling:
And hex nut removed, using the supplied Allen key to loosen the set screws (one of which you can see on the top of the coupling):
With that done, the coupling can be slid/tapped onto the gear shaft inside the box, and the hex nut screwed on and torqued to hold the coupling in place (and then set screws also tightened). In order to torque the hex nut, the gears have to be immobilized.
Coupling in place:
And then the overdrive can be installed. Not difficult to do, but slightly awkward. Global Roamer recommend doing this from below, which I did using a jack to lift the overdrive as high as possible, and then, lying across the passenger seat, lifted the heavy unit into place from above. Doing this from above also made it easier (for me) to turn the gears by hand so that all would fit together. The coupling has to mesh with a gear inside the Roamerdrive main body, and the main body's gear has to mesh with a gear (that's out of sight here) in the transfer box.
Regarding the mounting bolts, the instructions state that on "some early transfer cases the holes may not be tapped deep enough and a 3/8 - 16 UNC tap may be required to clean the holes, or the bolts shortened slightly." As my transfer box is a 1960, I had to assume it may be what is considered an early version. Not having the specified tap, and not wishing to go and buy one just for this job, I tried to measure the depth of the holes with tape wrapped around the threads when reaching maximum depth, compared with the existing original studs. Everything seemed to be exactly matching, but not being 100% sure and not wanting to risk shearing off a bolt in the transfer case, the bolts were shortened by 3mm each (and were later fully torqued without problem). It might be a nice idea if shorter bolts could be included with the package for those unsure, as well as perhaps a more specific definition of what constitutes an early transfer box, given that the Roamerdrive will also fit Series 1 vehicles.
As forewarned in the instructions, being a left-hand-drive (LHD) vehicle the overdrive comes very close to touching the handbrake rod that you can see over the top of the unit. I've temporarily wrapped a strip of Velcro around the rod where the two come closest, to stop any contact vibration.
Things became a little more interesting when it came time to install the overdrive stick shift. The stick rod itself screws into a cast pivot that angles the stick 'inwards' towards the driver (in an LHD vehicle). However, when the stick was installed this way in my particular vehicle, with its kinked gearshift, two things happened: 2nd gear couldn't be selected because the gearshift contacted the overdrive knob. Secondly, in 4th gear, when the overdrive was selected to 'on', the overdrive shaft fouled the gearshift.
The solution turned out to be to reverse the pivot casting. This turns the overdrive stick shift angle 'outwards', and clears the gear shift at all times. However, because of the shape of the pivot casting, this means that the position of the hole in the tunnel cover has to change from that in the instructions, which indicates to center the hole precisely on the axis of the overdrive gearshift pivot. The hole now has to move upwards by a little to clear everything.
To find the exact location required, the time-tested method of making a pattern was used, with cardboard the same thickness as the aluminum of the gearbox tunnel cover.
Below, the cardboard pattern in place:
Roamerdrive stick clear of the gear shift both when on and off (stick in 4th gear here):
Then comes the cutting of the hole, and hoping the pattern was accurate:
Global Roamer supply a rubber cover to help block the hole. All that had to be done was elongate the hole downwards slightly using an X-Acto blade, and thanks to the rubber's flexibility it fit without a problem.
Once that was done, and clearances etc. checked, the floor panels were replaced, and took the Series out for a test drive. After a period of testing at slower speeds and different gears on back roads, there was a bit too much traffic on the faster roads to really give the overdrive a good test, but at 80 km/h (50 mph) it certainly made the Series a quieter and calmer place, and easy to see how 100 km/h might be achievable.
After the test, the transfer box external surface temperature on this hot and humid day was 55° C; the Roamerdrive was exactly 10° cooler, at 45° C.
On a later test drive on the faster roads, with two adults on board and into a very mild headwind, the vehicle achieved 95 km/h (59 mph) on level paved road, and that seemed to be the limit with the existing drive train components. The vehicle was at comparative ease at 85 kmh (53 mph) and would have done that all day, which is just perfect for me. With the 28% rpm reduction in 4th gear that the overdrive provides, that means that at 85 kmh the engine was turning at the same rpm's it would have used at 61 kmh (38 mph) before the overdrive was installed.
A few views of the completed installation (minus rubber hole cover):
Finally and perhaps most importantly, a view from the driver's position:
