Loose bearings
 

Need some help with wheel bearings on my 91 300E. Seems my front wheel bearings loosen within 1000 miles after adjustment. Someone explain to me what I am doing wrong or how to do right. I have repacked wheel bearings and replaced wheel bearings using the procedure in the manual. No matter if I repack or replace, seems the bearings loosen within 1000 miles or less. When I say loosen, I grab the at the top and push/pull vigorously. I can feel movement and hear 'clunk'. I purchased and used a metric dial indicator the last time and tightened to an indicated .02mm. Everything seemed fine for about 750 miles and when I re-checked, loose again. Talking with the local MB techs, seems i may not be tightening the bearings enough on the initial setting. The manual states to tighten bearings until they turn "with effort", loosen and then tighten to .02mm. The MB techs @ the dealership dont use the dial gauge and they say that they have no problems with come backs. Is this true or does every 124 out there have loose bearings?
Any help or suggestions would be appreciated. I have replaced all tie rods, drag link and rebuilt the idler arm. The front end is tight enough that the loose wheel bearings can be felt.:confused:

I concur with the MB techs. I don't use a dial indicator either, but the again you get the feel after several hundred times. I suggest you use the factory method for safety sake. There are two keys to remember. Don't over pack the hub with grease and tighten and back off the nut several times before you set the final preload. Tighten the nut down with about 45 ft lbs, spin the hub, back off the nut, re-tighten to about 45 again, spin the hub, back off the nut, and do this several times before setting the bearing to specs.

I've never used a dial gauge to check freeplay and I've changed and adjusted front wheel bearings on my 123, 124, and 126 models for over 20 years and I've never had a problem. It's kind of hard to describe how they should feel, but that said I tighten them real tight initially and try to turn hub to get them to seat. Then I loosen and tighten again. Go thru that process several times, then tighten till they are hard to move and then back off maybe 1/2 turn and then turn to tighten till you feel the adjusting nut starting to seat. Then put wheel on and spin it around a few times and then grab tire at top and bottom and feel for freeplay, to do this I remove brake pads. Keep in mind that I'm not a professional but this seem to have worked for me for a very long time.

Well, you do it just like a professional. As a professional, I can't recommend this method, but is how I do it.The only part I would say is not necessary is removing the brake pads, but if that is your comfort level, keep doing it.

I believe the only answer can be that the bearing races weren't seated properly. Ron is correct. When you put the nut back on, you're supposed to wrench it hard while turning the wheel (or rotor), until it is difficult to turn the wheel. This seats the races and squeezes the excess grease from the working contact surfaces so the clearance can't creep any further during use. Only then do you set the clearance.

Don't worry about damaging the races this way, they can take it.

I am glad you guys do it this way as well... tightening and backing off is the only way I have ever done wheel bearings.... I don't think I have ever replaced one

Hi
If they keep getting loose they might be too worn?
Regards, Bruno

If a bearing loosens up from wear, then that bearing has very serious problems and will destroy itself in short order. Anything less than the original honing marks on the race, and the bearing will go south rapidly. Bearings don't wear as you may think of other wear parts (journal bearings, seals, ball joints).

i am wondering
 

if it was run with the bearings loose the race might be worn between the race and the hub.

tom w

You're out of your freakin mind. You don't seat races by tightening the nut. You seat races by pressing or hammering them home with a race installer. Then you install the bearings and set the preload by the means that have been described earlier in this thread.

easy there
 

autozen

i bet he meant to seat the bearings against the race.

tom w

Actually, its unlikely that you can sufficiently accurately seat the races using either a press or a drift. Nothing will apply the pressure as evenly as the actual adjusting nut, when a few thousands of an inch clearance is the spec. It IS the races you are seating properly - the bearings do not need 'seating' between their mating parts, so the 45 ft-lb torque would accomplish nothing if this were the case.

Steve

Ok, Tom, I'll back off til I get an answer. I'm just concerned about seriously bad info about something as important as wheel bearings. I once saw a DIY tighten wheel bearings down to tight and go for a test drive. He ruined all the spindles and bearings, but what concerned me most was that he could have killed someone. We professionals take our job very seriously. I have always maintained a standard of sending out a car knowing that I have done my best to be sure nobody was ever stranded or at risk, because I was lax in my diagnoses. Anything less comes from a pseudo professional.:)

Where are you people coming from?

I disagree. The O.D. of the race is smaller than the hub. You must freeze the race if you want it to fit at room temperature. It will expand and effectively be clamped in place by the hub. When a mechanic "hammers" the race into place with a drift, he is attempting to overcome the interference fit between the race and the hub. There is quite a bit of force that secures this race and there is zero clearance between the OD of the race and the hub.

Tightening down on the adjusting nut won't move the race within the hub whatsoever.

The procedure of tightening the adjusting nut past the desired operational point is to ensure that the hub is fully seated against the inner bearing. If you simply brought the nut up against the face of the outer bearing, you could be misled by any clearance that existed between the rotor/hub and the inner bearing. Once all the clearance is definitely zero (or negative), then you can back the nut off and set it properly to the desired operational point (.0005" end play IIRC).

You could use a dual set of angular contact ball bearings like I do when I manufacture my spindles for balancing jet engines. The set costs $3000. But, you just clamp the outer races together and the two bearings load themselves up with the proper preload and the internal clearance is zero. The bearings run fantastic in this situation and they are eminently suitable for measuring unbalance that approaches .000010" displacement of C.G. Truly amazing. This could never be done with a tapered roller bearing that requires clearance to run safely.