Wheel Bearing Removal - PeachParts Mercedes-Benz Forum

#1 07-30-2003, 06:10 PM

Hey guys,

Just working on bolting up my W123 300D brake parts on my W115 220D. I removed the caliper, and hub dust cap, and the locking nut. I slid off the first wheel bearing. Trouble is, I cant slide off the rotor/hub assembly because the second wheel bearing seems to be wedged in there. My Chiltons manual doesn't provide any helpful insight in the removal of the second, rear wheel bearing. Any tips?

And secondly, I can "repack" these bearings by applying a liberal amount of grease to them, no?

engatwork · #2 07-30-2003, 06:37 PM

You ain't pulling hard enough. You have to grab it in the 3 and 9 o'clock position and pull like all get out. It will come off. You can repack the existing brgs. There is a certain amount that it calls for and putting too much can overheat them. If you have never done it before find someone that has packed wheel bearings to walk you through it the first time. Pretty straight forward.

#3 07-30-2003, 08:02 PM

Okay, thanks for the help.

I got it off with some might ... but I already repacked one bearing and probably put too much on. I applied a pretty liberal amount of grease ... but not too much. I have no one to teach me. I will repack the second bearing with less and see what happens I suppose.

Danke!

engatwork · #4 07-30-2003, 08:37 PM

It is not really how much you pack in the bearing because you can only get so much in there. It is everywhere else that you want to be particular about. Don't fill the cap all the way up. I usually just put some in there up to the "edge" where the inside diameter changes. I usually just coat the spindle and inside of the bearings good. I just brought this up because there is a "capacity" rating per wheel. Don't have the info here in front of me though. Personally, I have never weighed it when I have redone one.

JimSmith · #5 07-30-2003, 10:51 PM

Cazzzidy

The intent of packing a bearing with grease is to provide lubrication and cooling to the interface between the loaded balls and the races. Grease is used to avoid the need for a forced or pumped oil lubrication system, and is a very practical, robust and inexpensive solution when it is carried out according to plan.

Grease works by storing the base lubricationg oil in a suspension of thickeners, chemical stabilizers and other materials. The oil is released by increases in bulk temperature to replace the oil that is used by the bearing. "Using" the oil occurs when the oil molecules are heated to very high temperatures and subjected to very high pressures and mechanical loads, which occurs in the film between the ball and the race. Under these conditions the oil molecules are broken apart, oxidized and turned into stuff other than oil. Some also vaporize and condense elsewhere, often outside the area where they can be returned to duty. The stabilizers and "other materials" are intended to protect the oil molecules from being oxydized or mechanically ripped apart by the extreme conditions in that film between the loaded balls and the race. The science of tribology and these additives is a little like the dark magic of witchcraft - I am not convinced these things are "designed" as it seems they are mostly the result of lots of trials, tests, and, with the good formulas, a healthy dose of luck.

As the bulk temperature of the grease increases the oil comes out of suspension from the stored grease adjacent to the bearing and runs into the area where it is needed. This cools the bulk mass down and the grease stiffens up again, and stops bleeding oil. Until it is needed again.

So, you need enough grease, in the right places in the bearing and the bearing cavity, to fulfill this job for a significant period of time. There is also a role as a heat transfer media to draw heat away from the bearing and spread it to adjacent surfaces to help cool the bearing. Grease is generally much better than air at this function.

Normally as you run a bearing after packing it, the bulk of the grease you packed in the bearing itself is forced out of the bearing and comes to rest in the adjacent housing volume, where it can readily supply that oil as it is needed by the process noted above. If the bearing is packed correctly, and then the adjacent volume in the bearing housing is packed full of grease too, there is no place for the excess grease in the bearing to go. As a result it ends up being churned like butter as it is dragged around with the balls and cage. This creates excess drag, and the energy you put in to overcome the drag goes toward heating the larger volume of grease. In this situation there is no need for the oil in the bearing, as it is already full of grease and oil, so the oil runs to some other part of the housing (and usually leaks out the cap), which makes the remaining stuff thicker, creating more drag, more heat, and so on.

This condition eventually defeats the original "design" of the grease lubrication system and you get a rapid loss of lubricating oil, while the bearing itself is still full of thickeners and chemical additives. Since oil from the adjacent "fresh grease" cannot run into the bearing because it is blocked by these thickeners, as well as the overall grease pack inside the housing, there is no means to lower temperatures.

Most thickeners and additives are not lubricants (thickeners are typically fine clay particles or metal based soaps, neither of which is a lubricant by itself), and as, as noted, the oil all runs out so the bearing keeps getting hotter and fails. The key is not to overfill the actual housing. I have seen many automotive rolling element bearings packed solid with grease, and as long as the housing is not more 25% or so filled, the bearing works fine.

As engatwork noted, there is typically a volume, measured by weight of a specified type of grease, listed by the auto manufacturer for the bearing application. I am not aware of where this information is provided by Mercedes-Benz, but I would feel pretty comfortable packing the bearing itself "solid" and putting about the same amount of grease in the cavity or housing as I found when I opened it up. When handling the bearing it is best to go through great pains to keep it and the housing, as well as all the tools and the grease you use absolutely clean. This means you should use rubber gloves as well, as while you handle the bearing with bare hands you will off load a significant quantity of chlorides from your skin, as well as other acidic skin oils and greases. These chemical contaminants will rapidly deplete the additives in the grease, leaving the bearing vulnerable to rapid grease failure, and particulate stuff will quickly lead to mechanical failure of the races.

Good luck, and I hope this helps. Jim

#6 07-31-2003, 01:08 AM

That was one of the best, most informative posts I have ever read, Jim. It should be in a FAQ somewhere, as it completly explains the roll of grease in a bearing application, problems associated with it, and correct packing procedures. Bravo!

After reading that piece of art, I am going to pull my two "packed" bearings and try again. This time, I am going to soak the bearings in a solvent to clean them before re-packing. I will pack it to the brim, and give special attention to the assembly in which it will be working. Hopefully I can create a lubricating atmoshpere that will provide a clean, quiet, and cool rotation.

Thanks again, Cassidy

sokoloff · #7 07-31-2003, 06:47 AM

You really need to find the MB specs for the amount of grease. For my 123 body, I think it is only 60g per side which is hardly fully packed. In fact, if I didn't know the factory specs, I would want to put a whole lot more in there.

Len

JimSmith · #8 07-31-2003, 07:17 AM

Len,

When I noted the bearing is packed "full," that means the actual bearing, which will not hold 60 grams. By filling it you push grease in one side and look for it to show up on the other. This means you "fill" the space between the balls and the cage, which on a relatively small bearing like a wheel bearing, is a small volume. The rest of the grease goes in the housing. Jim

The Warden · #9 07-31-2003, 11:01 AM

When I did my bearings last January, I bought a 150 gram tube of grease from the local dealer and weighed out half into an old butter container, then put the other half in another container. I then packed the bearings, coated the spindle and races, and put the remainder into the grease cap. 7 months later I haven't had any problems with overheating or anything like that.

At time time, I was told that the M-B grease was special and to use it specifically. Given that the grease wasn't expensive, I don't see anything wrong with using it.

Just my $.02...good luck!

sokoloff · #10 08-06-2003, 06:41 AM

Jim - read your post a little too quickly. My apologies. I agree that the bearing itself needs to be packed well.

Len