While we were waiting in Kamanjab, I decided to do something about the portal axle oil pumping (both front sides have been pumping between 50 to 80ml through the breather into the front axle per day since we got here). I've had several ideas how to deal with this, but have been thwarted by what is available locally. Looking through what I already had "in stock", plus what the hardware section of the Shell garage shop in town had, I came up with an "African modification" - this consists of 2 banjo unions, some shielded fuel pipe, insulating tape, jubilee clips and wire wraps. Basically the portal axles are gearboxes with two large gears, the upper one sitting on the axle, the lower one driving the wheel hub. These gears sit within a housing which is quite a tight fit around the gears. sounds like a gear pump? Well it is - and there's a pump outlet in the form of the breather pipe which is right at the top of the housing and leads into the main axle. This is a known issue with this type of Mog - some do it, some don't. I didn't detect much pumping in UK, until just before we shipped the truck -the change may have been due to the new oil type I filled the portals with, or different journey types. The rate of pumping seems to depend to some extent on driving speed - my plan was to keep speeds below 70kph and therefore avoid oil loss. Throughout the trip I've been checking each portal every travel day before setting off and keeping records of oil loss, distances, speeds etc. Interestingly, even keeping speed down to 60kph or less still results in pumping - plus we had a seal leak leading us to change it in Swakopmund, this led us to needing more oil for the whole trip than we were carrying. The fully-synthetic oil we are using (Mobil 75w90 SHC-1) didn't appear to be available here, so we were facing the need to change it for locally available mineral oil (and that change would also have meant changing the axle diff oil too as it pumps into it). Luckily we found a Mobil agent in Rundu who ordered some of our oil in for us (after searching for weeks elsewhere), so thus relieved the pressure - but it's still not right having to continually refill the portals (and drain the excess from the diffs every now and again), so a mod wass needed.
The portal housing has the breather pipe at the top, a drain plug at the bottom and a fill/level plug somewhere between. In a gear pump there is a high-pressure area and a low-pressure area - by my reckoning the high-pressure area is around the breather pipe outlet and the low pressure area is in the region of the fill plug - so by linking the breather and the fill plug the oil should return to the portal rather than be pumped into the axle - I've tried this on the right hand portal and so far we've got 3 journeys completed - on the 1st it used 0ml, the 2nd 15ml and the 3rd 0ml (the second fill was on a slight incline so may have been misleading) - the left hand portal has continued to pump at around 40-50ml per trip. So it's looking like we may have found a solution - not technically the neatest, but a solution that will work in most circumstances - more testing/measuring needs to be done to really confirm our findings. This solution isn't robust enough for "off road use" as branches/stones could get caught in the pipework and cause damage, but it's easy enough to swap back to the original system when we know we'll be in these situations -and I've recently found what I've been told is "impossible to find in Namibia" - copper brake pipe - which could eventually get soldered-up to produce a more resilient solution.
If this all goes well, I'll be modding the left hand portal too after Moremi/Chobe to see if it'll fix that side too.