Preamble
Day to day driving in a Series Land Rover is done in rear wheel drive. 4wd drive is selected with either the yellow or red knobs depending on whether high or low ratio is required.
When in 2wd, only the rear axle is being driven and the front axle is idle. This is the most fuel efficient configuration.
Even in 2wd though, there is still significant mechanical loss through the idle front axle. Afterall, the front road wheels are causing the swivels, front differential, propeller shaft and output shaft to rotate as the vehicle travels along. This is all lost energy.
Fortunately there is a solution… Free Wheeling Hubs (FWHs). These devices replace the conventional drive hub and allow the driver to disengage the front wheels from the axle.
In this configuration, the front swivels, differential, propeller shaft and output shaft remain stationary. Only the road wheels rotate on their bearings.
Land Rover offered FWHs in the 1960s as an optional extra. These were manufactured by Mayflower Automotive Products (MAP) in Devon UK and latterly by Fairey Winches.
Whilst service kits and spares are still plentiful, original equipment MAP FWHs are now very rare.
Fortunately… Brazil have the solution.
AVM FWHs
FWHs are fitted in replacement of the drive flanges on the front axle. The mechanism inside allows the hub to be disengaged from the drive shaft.
The kit comes complete with all gaskets, new felt washers and a neat split pin for the castellated nut.
Fitting Free Wheeling Hubs
It’s worth putting some paper down at the this point as there could well be EP90 in the bearing housing (from the swivel hubs if over filled) which will drip out and make a mess.
At this point the drive flange should come free from the hub centre. It may need a tap with a soft face mallet to knock it loose though.
Whilst i was at it, I repacked the front wheel bearings with high temperature bearing grease from Penrite.
The next step requires the castellated nut to be torqued onto the stub axle. But with the hub now disengaged from the shaft, the shaft will just spin… even if you engage 4wd.
I managed to brace the end of a large flat head screwdriver between an outer spline of the stub axle and an inner spline of the FWH body.
Now everything is tightened down, the hub engagement body can be fitted.
This is held in place by 6 skinny bolts. It would be a very good idea to apply a copious amount of copper slip to the threads.
The bolts are steel and the hub body, some form of alloy… add some salt water in winter and you have the perfect cocktail for bimetallic corrosion.
That is pretty much it. The freewheeling hub is installed. A very straightforward addition and one that will improve fuel economy greatly, reduce cab noise and wear on the front transmission.
It’s advisable to engage the hubs frequently though so as the oil in the swivels, differential and output housing is splashed around a bit.
How do they work?
Using the pictures above as reference…
When the “switch”’on the outside of the FWH is in the 2wd position, the splined sleeve (left hand part lower picture) is retracted and does not engage with the outer splines of the drive hub (right hand part lower picture).
Once the “switch” is moved to the 4wd position, the splined sleeve engages with the outer splines of the drive hub, reengaging drive to the stub axle.
It is not recommend to drive with the transmission in 4wd and the FWH in 2wd.
Little Green Landy 
Hello,
Thank you for this very detail post.
As it is very debated, do you really get an improvement on the road with FWH ?
What kind exactly ?
KR,
Gilles.
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Hi Gilles, it’s a bit early to tell if there’s an improvement on MPG. Logically, with less mechanical resistance, the motor has less work to do. It certainly accelerate quicker (by series Land Rover standards)… but in there lies the problem… one needs to maintain a conservative right foot. I’ll post some stats on MPG in a few months. Best. LGL
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Hi LGL,
Thank you for your reply.
Good idea to share some data in a few months and also about smoothness of the steering.
KR.
Gilles.
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Hi there nice blog, be using your rebuild advise as I’m also rebuilding my 1964 S2A, i removed my AVM as always had trouble with them Bolts seizing, bolts stripping where Allen screw fits, the last straw was filling hub up with water, water would sit and seep into hub where gasket leaked.
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