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Hummer Knowledge Base

The Hummer Knowledge Base

How to Change Hub Oil


Y ou can check the hub oil without removing your tires on the right front and left rear only. But on the left front or right rear you can't because they are aimed the wrong way. You MUST remove the tires before you can drain any of the 4 hubs. I keep my eyes on the hubs that I can check easily without removing the tires and if they become contaminated then I remove the tires and change the oil in all 4 hubs. If you do any water fording check for contamination often! I get water in mine everytime I go play in the creek. I am told that it should be sealed and shouldn't leak but I am told by others that the hubs always leak. So armed only with my personal experiences, MINE ALWAYS LEAK! So my advice is to check them often, it's easy! I don't see a recommended time to change these fluids in the chart in my Hummer service manual, it says to check the hubs for leaks every 3000 miles but I guess they think the oil in there will last forever?? It won't! My advice, check it often!


click on pictures to make them bigger

I f you have CTIS it is a little harder because there are a few extra steps to disconnecting the air lines so the tires can be removed. First put your CTIS tire selector on the OFF position, this disconnects the front and back airlines from each other. Then remove the CTIS triangle shaped cover using a 5/8 or 16MM socket. Next push the air disconnect button (silver) on the center where the air hose comes out of the center of the wheel, the center should pop out about 1/2 inch when the button is pressed and that tire will be isolated from the rest of the system! NOTE: the little silver button is called a quick disconnect but it doesn't actually physicly come apart! Don't pry it apart!!! It only disconnects the air flow to that one tire...( Push the disconnect button on ALL the tires before proceding to the next step!) Then to remove the hose from the wheel use a 3/4 open end wrench to unscrew it. If you hear alot of air hissing when your doing this then you didn't push the silver botton on your other tires or don't have the tire selector set to off...


click on pictures to make them bigger

Y ou will need an impact wrench to remove the tires, the threads are diffrent on the hummer from anything else and the Lug nuts are very hard to get off without an impact wrench, they seem tight the whole way off, unlike a normal car that spins freely once they are loose. I wouldn't want to try and get a lug nut off with a hand wrench, much less all 8 on one tire, much less all 32 on the truck to do this oil change! AARGH! But the impact does make it easy, thats why Allan here at our Car Stereo shop borrowing my impact wrench! The lug nuts use a 7/8 inch socket. You will need to jack the vehicle up to remove the tire, the Hummer jack is OK but a good floor jack is alot less work or even a good HI LIFT jack would be good (every serious offroad vehicle should have a HiLift right?) . In the pictures above you can see Allan removing the Tire, in the second picture you can see the fill/check bolt hole (#1) on the geared hub. When inspecting your oil level the oil should not gush out of this hole, it should be slightly below the hole! The oil should be a nice color, if it is whiteish or way above the fill line your oil is probably contaminated with water! And a picture of Allan removing the drain plug with a 5/16 hex socket (#2) . If you want to clean really good inside the hub you can remove the side cover the plate which is held on with 8 bolts ( the plate with the fill plug in it) but we didn't think Allan's truck needed that much cleaning this time. The drain plug for the hubs, like most drain plugs in the Hummer is magnetic so examine it for metal filings and clean it off, put the drain plug back in and fill the hub till you get to the fill hole with multipurpose gear oil SAE80-90W (1 pint ) then put the fill plug back. Then remount the tire, rehook the air stuff if you have CTIS. After you screw the CTIS tube nut into the center of your wheel with your open end wrench (on all 4 wheels) then push in the square coupling and it should re-engage and the little silver disconnect button should pop back out. I have heard many reports of CTIS systems leaking but so far I have not had any leaks at all in my CTIS system.


W hile Allan was under there he drained and replaced his oil in his Axles (differentials) it uses the same gear oil as the hubs and is easy to do! The drain is on the bottom and is a 3/8 inch hex and they hold 2 quarts of gear oil.


Last minute update!


Scott Weiser made some last minute points just as I was going to upload this to Bob!
I don't want to redo the whole stinkin page so I will just throw Scott's text in here at the bottom!
It is important stuff!!! (I knew I would forget something!)

When you change the hub oil, you should check the spindles for tightness to see if the spindle nut has loosened. To do this, with the wheel off, use a pry bar over the drag link and under the spindle flange edge and try to wiggle the spindle up and down or in and out. There should be no detectible play in the spindle. Also look for "weeping" in the spindle seals and check your vent tubes for damage/crimping, along with checking the torque on your upper and lower ball-joint bolts. Just a note, it's a good idea to put the bolts into the balljoints from the *bottom*, with the nuts on top, so you can see if they have loosened up during pre-trip inspections. My first trip to Moab, one vehicle was disabled because the upper ball joint on the right rear wheel ripped out of the upper control arm, which was caused by a missing and several loose bolts, allowing it to "slop" about.



Thanks to Allan Madar for letting me take his picture while working on his Hummer with my tools.
Thanks to Micheal Selig for suggestions writing this tutorial
Thanks to Jack Rickard for telling me how to do the big/small pictures.
Thanks to Scott Weiser for waiting 'til the last minute to let me know all the stuff I forgot! :-)
Thanks to Bob and ALL the HML list members for everything!


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