Front Portal Axle Lubrication Mod
The front portal axles of some ex-military mogs pump their oil out through a breather pipe into the main axle. We found that ours did this, but only once we'd arrived in South Africa. We monitored it, filling the portals up every day and measuring how much each side was using.
We found that we were using between 50 to 100ml per side every time we drove any great distance. As each portal only contains 200ml when full and we were only carrying 5l of the special oil that we had filled the axles with, it was time to do something.
Talking to other Unimog owners that we met en-route we heard of many different possible solutions, including detaching the breather from the axle and attaching it instead to new clutch fluid reservoirs to act as header tanks, welding up old shock absorbers into an in-line oil catchment device. Thinking about what was actually happening, it would seem that the fit of the gears inside the portal housing is probably quite tight, so the gear pair are acting in the same way as a gear-pump, with a high-pressure area in one part of the portal and by corollary a low pressure area somewhere else. The fact that oil was being pumped upwards throught the breather pipe indicated that the high pressure area coincides with the location of the breather tube.
There is also an oil-filler/level plug which is much lower than the breather. We wanted to link these two points to try to get the oil to flow back down to the lower levvel from the breather pipe rather than going all the way into the axle, initially we wanted to do this using copper pipe soldered together to form a "tee", but try finding copper pipe in Namibia....... Finally we found some "banjo" unions that fitted the level plug and the breather point, so fitted them and linked them using stainless shielded flexible tube joined via a tee-piece at the top to the axle vent. The logic of this is to allow any over pressure to vent but to allow any oil being forced out by the high-pressure area of the portal to be literally sucked back down by the low-pressure area which looked like it would probably be around the level plug area. The picture shows this on the right hand wheel - we only had enough kit to do the one side.
The results were instant and dramatic - this wheel stopped losing oil altogether whereas the left hand side (unmodified) continued to lose oil.
The plan now is to kit ourselves up with enough parts to be able to modify the right hand side in exactly the same way. The downside of this solution is that the flexible pipes could get caught and damaged by branches or stones thrown up by the tyres when driving offroad. The instant solution is that the current mod is easily removed and the truck returned to original for those times that we will be in more difficult terrain, however it should also be possible to solder some copper pipe to replicate the flexi-tubes to create a more robust piece of kit. We'll be taking this out as well.
October 2013 - After much searching I managed to complete the mod kit for the other axle (strangely the hardest parts to find in Africa were jubilee clips - but we eventually located some of the right size in Iringa in Tanzania). The mod was applied and is now working succesfully - we've since done about 2000km of hard driving all the way up Tanzania in 5 days without any oil loss.
The front portal axles of some ex-military mogs pump their oil out through a breather pipe into the main axle. We found that ours did this, but only once we'd arrived in South Africa. We monitored it, filling the portals up every day and measuring how much each side was using.
We found that we were using between 50 to 100ml per side every time we drove any great distance. As each portal only contains 200ml when full and we were only carrying 5l of the special oil that we had filled the axles with, it was time to do something.
Talking to other Unimog owners that we met en-route we heard of many different possible solutions, including detaching the breather from the axle and attaching it instead to new clutch fluid reservoirs to act as header tanks, welding up old shock absorbers into an in-line oil catchment device. Thinking about what was actually happening, it would seem that the fit of the gears inside the portal housing is probably quite tight, so the gear pair are acting in the same way as a gear-pump, with a high-pressure area in one part of the portal and by corollary a low pressure area somewhere else. The fact that oil was being pumped upwards throught the breather pipe indicated that the high pressure area coincides with the location of the breather tube.
There is also an oil-filler/level plug which is much lower than the breather. We wanted to link these two points to try to get the oil to flow back down to the lower levvel from the breather pipe rather than going all the way into the axle, initially we wanted to do this using copper pipe soldered together to form a "tee", but try finding copper pipe in Namibia....... Finally we found some "banjo" unions that fitted the level plug and the breather point, so fitted them and linked them using stainless shielded flexible tube joined via a tee-piece at the top to the axle vent. The logic of this is to allow any over pressure to vent but to allow any oil being forced out by the high-pressure area of the portal to be literally sucked back down by the low-pressure area which looked like it would probably be around the level plug area. The picture shows this on the right hand wheel - we only had enough kit to do the one side.
The results were instant and dramatic - this wheel stopped losing oil altogether whereas the left hand side (unmodified) continued to lose oil.
The plan now is to kit ourselves up with enough parts to be able to modify the right hand side in exactly the same way. The downside of this solution is that the flexible pipes could get caught and damaged by branches or stones thrown up by the tyres when driving offroad. The instant solution is that the current mod is easily removed and the truck returned to original for those times that we will be in more difficult terrain, however it should also be possible to solder some copper pipe to replicate the flexi-tubes to create a more robust piece of kit. We'll be taking this out as well.
October 2013 - After much searching I managed to complete the mod kit for the other axle (strangely the hardest parts to find in Africa were jubilee clips - but we eventually located some of the right size in Iringa in Tanzania). The mod was applied and is now working succesfully - we've since done about 2000km of hard driving all the way up Tanzania in 5 days without any oil loss.