SEE FYI - Front portal axles lubrication issues

[peakbagger]

FYI, While roaming other Unimog websites a known crops up about the front portal axles losing fluid. Its reportedly an issue with Military Mogs of the 406 vintage and going on into the later SBUs, including the SEE. There is a possibility that the front portal boxes will slowly pump their fluid into the differential housing which will lead to the fluid getting low in the portal boxes and eventually portal gear damage. It seems to occur mostly on units run at road speeds so this may not be applicable to those using SEEs at low speed. There are a couple of choices for a fix, the no cost one is check the portal axle fluid level frequently if used at road speed, or the permanent fix is to install modified breather tube assembly's that separate the gearlube in the vent tube and reintroduce it back to the portal box. Vons Mogs and Expedition imports both carry modification kits and I expect someone willing to chase parts with the capability to braze tubing could duplicate a similar system. I plan to install modified breather tubes on my 1300 but will probably just keep an eye on the fluid level of my SEE.

 

[The FLU farm]

Thanks, peakbagger. Hopefully that info can help save a few FLU owners from expensive repairs.
I'm playing it really safe, by checking the levels and driving slowly.

 

[LZahariev]

What is the correct way to check the fluid level in the portal box of the axle? What type of fluid would be used to top off?

 

[The FLU farm]

Don't take my word for it, but what I did was remove the level plug, and if nothing came out I added some sort of 80W/90 I had handy through the filler plug until it came out at the level plug.
Probably should pull the drain plugs and start fresh at some point.

 

[peakbagger]

If you downloaded the manuals there is a Lubrication Order. Page 16 of 38 has an illustration of the portal axle plugs. In general its a very valuable and thankfully short (only 38 pages).

If you are laying under the truck there are three threaded plugs on the back of the portal. The lowest one roughly on the center of the axle is the drain plug. The one that is higher and to the rear of the truck is the check plug. The higher one towards the front of the truck is the fill plug. With the truck in 2WD, open the check plug and the fluid should be level with the bottom of the hole. The easiest way is open the fill plug and add fluid until it drips out of the check hole.

The portals dont hold a lot of oil and and this is probably the most critical place to check fluid level on the vehicle. The standard recommendation is 80/90 synthetic gear lube, I use Mobil One. It doesnt take a lot to change it out. The folks who run Mogs at road speed are paranoid about the portals as if they fail, the truck isnt going anywhere and repairs are expensive. Most folks carefully drain and change the portal fluids routinely and inspect what comes out for any metal chips or other foreign objects. For a SEE that has sat for many years its definitely a must change. The air system pressurizes the axles and portals while in 4WD and since the SEE does not have an air dryer, water build up in the air system is likely and eventually it can get into the portal and axle oil. Oil floats on water so you could be topping off a blend of oil and water so I strongly recommend draining and replacing once to deal with any water build up that occurred over years of sitting.

FYI while you are under there go through the rest of the lube instructions and locate all the grease fittings and give them a squirt, heed the warnings on overlubing. The rear thrust ball joint (page 18 fitting is a PITA to find, the only way I could get to it is via the back of the cab area from above. I needed to deploy the backhoe to get down in there. I expect since its such a PITA to get to that it doesnt get lubed. All the fittings shown should be there, if you cant find them you need to look more carefully or they may be snapped off.

 

[LZahariev]

Thank you for the info.

 

[Pinsandpitons]

I like pictures.

 

[peakbagger]

I agree !