Hubs

If you do not plan to detach the brake calipers from the brake system, you can hang them from the truck body with baling wire.  Also, the bolts that hold the caliper to the hub are tight, so a robust, hardened socket and breaker bar with cheater will be required.  In this photo, the bottom bolt was the zero-clearance body bolt.  Insure you note which hole it came from so it can be reassembled the same way.  Also, during reassembly, be sure to use anti-seize on the bolts and nuts.  You will thank yourself later.  Build air pressure and engage the differential lock.  Remove the cotter pin and loosen the castle nut while the assembly is still on the axle.  The first time we did not do this and it makes things harder.

The hub assembly is heavy and you should consider using an engine hoist to lift it during the service process.  It saves the back and prevents it from being dropped on your foot possibly damaging your foot or the hub casing. One of those two is replaceable, the other is not.  To separate it from the hub mount required some rubber mallet work to crack it loose.

We cleaned and inspected the old hub casting and found it damaged beyond further use.  A used casting was obtained from Rob Pickering at Terry Lee Enterprises and was cleaned and ready for installation.

The smaller roller bearing installed in the housing.  This is also called the upper outer bearing.  It gets tapped in with a plastic mallet and soft metal punch or bar.  Easy and slow will win this battle; you do not want the bearing cocked in the cup as it is hard to get out.

Next, the driven gear is placed in the housing gears down (out) and the lower inner bearing is tapped onto the gear shaft and into the housing.

The bearing is seated but the gear will need to be driven back into the bearing.  You will have to brace the bearing to prevent it from being pounded out.  Civilized mechanics use a hydraulic press and we would have as well if we had access to one.  Instead we used a dead-blow mallet and some time.  Slow, but it did work.  You can also use the castle bolt and wear ring to help seat these parts together.

This is the "lower outer" roller bearing that always seems to fail first.  This is a big bearing, but it does not have an inside race.  Sadly, Mercedes elected to use the surface on the driven gear as the inner race thus assuring that when there is wear you have to replace the whole gear rather than just a bearing.  Look carefully at the photo above and you will note that there is a plastic retaining ring on the inside.  This ring holds the rollers in place until it is time to slip over the wheel gear (driven gear).  Inspect the next photo carefully and you will note the ring being displaced as the bearing is being seated.  Note the castle bolt next to the bearing grease at the top of the photo.

To seat the outer lower bearing we used a small punch and then tap-tap-tapped our way around the circumference of the bearing repeatedly to get it to seat.  We coated both the outside of the bearing and the inside of the housing with a light coat of axle grease to prevent binding.  Note that the retaining ring for the rollers is being displaced as the bearing is being seated.   This prevents the rollers from scattering to the four winds during the process.  The hub bolts were screwed in to allow moving the gear if required.  There several things going on at once during this process.  You are seating the bearing, but you are also seating the gear into the lower inner bearing at the same time.

The same process a bit further along.  Note that the retaining ring has popped out while the constellation of rollers are in place.  Also note the retaining bolt that goes through the center of the driven gear.  SUGGESTION: it is easiest to loosen the castle nut on this while the hub is still attached to the axle.  With full air pressure, engage differential lock and get your hardened socket with breaker bar and crack it loose.  Likewise, tighten it to full specified torque after it is back on the truck.  See shop manual for specified torque (it will be tight).   BUT YOU HAVE TO REMEMBER TO TIGHTEN IT.  This bolt holds the driven gear in the hub casting and if it is loose nothing good will come of it.  And remember to install the cotter pin after the castle nut is tight.  Also note in the photo above just above the hub casting is the wear ring.  The wear ring provides the seal between the spinning gear and the lower outer oil seal.  The ring is shown with the hump up on the table.  When assembled, the hump fits into the grooved area in the driven gear.

Installing the wear ring and the oil seal requires keeping the wear ring in place while the seal is tapped in with a punch and mallet.  Slow and easy wins this battle.  Put a light coat of grease around the circumference of the wear ring and on the inside of the seal.

THIS IS THE WRONG WAY TO DO THIS!!  We had not deduced the "use the axle and diff lock" technique yet.  The vice could not hold the axle shaft sufficiently tight to provide full torque.

This is the better way.  Hand tighten the gear to the axle with your allen wrench.  The bearing should already be on the gear.  Stick the assembly in the axle, engage diff lock and tighten the bolt to the full torque specification.  Note the pocket in the hub mount below; the associated gear is held into the hub casting via the castle nut described above and will be seated when the assembly is bolted to the mount.

The finished hub assembly is being lifted back onto the hub mount.  Note that the wear ring and outer lower oil seal have been installed.  Also, the castle nut has been installed and tightened.  I recall that in this case, I tightened the nut by installing several hub bolts and using them as a fulcrum for the tightening process.  Using the diff lock is safer, easier and will allow you to easily check the torque. WHEN YOU GET READY TO REASSEMBLE THE UNIT, DON'T FORGET THE GASKET SEALER.  IT WILL LEAK UNLESS YOU USE SEALER.  Apply the sealant around the entire face of the casting

Time for the final assembly.  Note that the hub bolts are special.  Not only are they hardened, but they have a neck-down as well.  Insure that these are clean, free of debris and that the threads are not damaged.

Next install the caliper(s).  Remember to put the body bolt into the same location and to use anti-seize on both bolts and nuts.  Then install the stone shield at the back.

Next comes the brake rotor and the hub.  Getting these aligned is hard, we used a hydraulic jack as an adjustable support for the heavy rotor to make life easy.  You can see the jack at the bottom of the photo.  Once you can get 2 bolts on opposite sides in, the balance is easy.  The hub will have to be tapped into position as it is an interference fit inside the rotor.  INSURE THAT THE HUB BOLTS ARE TO THEIR FULL SPECIFIED TORQUE.  These bolts hold the wheel to the axle and if they are loose bad things will happen next.  I also suggest that you use anti-seize on these bolts.  They are difficult to get out if they are rusted; you will break sockets and/or breaker bars trying (ask me how I know).

If you are really good and you have your act together, all the correct tools and parts and luck is with you, you may be able to complete a hub service in about 10 hours.  These conditions are rarely, if ever, likely to occur so 2 full days would be a good execution time although it will likely be longer.  If you do this outside, be sure to cover your work with a trash bag and tape or a tarp and bungees to prevent rain or dew from contaminating the components.

Doing a hub is a real hassle.  We have been fortunate that the failures we have had were sufficiently close to a shop that we did not have to do this on the side of the road.  There is some good in every bad situation I suppose.