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W124 Front Wheel Bearing

Discussion in 'Wheels, Tyres, Brakes & Suspension' started by Number_Cruncher, Sep 19, 2008.

  1. Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    While fitting new brakes at the weekend, I found a problem with one of the front wheel bearings.

    I had jacked up the car, and felt the wheels prior to the MOT, and found them all OK. The car passed its MOT that morning just before I began to replace the brakes.

    Even with the wheel off, and turning the disc, I felt nothing unusual, but, when I took the disc off, and began to wire-brush and clean the face of the mounting flange, I found the bearing felt really quite rough to turn. D'oh!, I found the problem just approching midday on Saturday, as every decent local bearing stockist was closing! :mad:

    Attached (hopefully!) is a piccie of what I found in the smaller, outer bearing; the outer race is badly pitted, and the roller just to the right edge has failed quite badly. The main cause of the roughness was actually flakes off the failed roller wedging themselves under other rollers. The odd thing was, there was no noise in the car, and the bearing felt OK when felt by rocking and turning the wheel.

    I'm really glad that I caught this before the bearing locked, and spun the inner race on the stub axle. The only indication that there was anything wrong was the roughness which was only felt at hub radius - you couldn't feel it with the disc in place.

    Upon re-assembly, with new bearings in place, I set the end-float to MB's spec of 0.01mm using a dial gauge, and I can confirm that there's no way anyone can meet the spec by feel alone; without using the gauge. You can't feel 0.01mm of free play when there's grease in the bearing - no way! - but, it shows up on the dial gauge plainly enough.

    The bearings themselves are quite easy to replace - there's a decent lip to get in with a drift to knock the old outer races out of the hub, and, when pressing the new ones in, you can use the old outer races as spacers, because the races don't sit deeply recessed in their bores. The only thing to be at all wary about is making sure that you don't damage the ABS teeth - oh, and, as ever, maintaining scrupulous cleanliness when dealing with the new bearings!

    View attachment 11995
     
    Last edited: May 28, 2011
  2. grober

    grober Hardcore MB Enthusiast

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    Good post-should maybe go in the how to section?? Altho some more pics would have helped. Maybe difficult to take pics when your hands are covered in grease?;)
     
  3. kth286

    kth286 Hardcore MB Enthusiast

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    Number Cruncher

    Good post.

    How long would it take to replace a front 124 bearing assuming starting from when the car is on the ground on all four wheels.

    Job will be done on the ground just using Mercedes jack and the use of an axle stand.

    Thanks
     
  4. Frank O' Phile

    Frank O' Phile Hardcore MB Enthusiast

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    Mine went almost the same way. Only a couple of days after passing the MOT the rumbling started suddenly. None of that faint whining, wondering whether a bearing might be on its way out. This started so quickly I thought a caliper had fallen off.

    Replacement is straight forward enough and can be done on the ground and the only real problem is finding the right tools for knocking out the old races. I would guess at 2 hours start to finish, with a coffee break of course.
     
  5. kth286

    kth286 Hardcore MB Enthusiast

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    Good - not long at all then.

    Thanks for that.
     
  6. OP
    OP
    Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    Yes, I think 2 hours is a reasonable estimate to do it on a driveway, without rushing - in a workshop, much faster, I would hope to have both sides done in that time.

    I found that the brake disc came off the hub without putting up too much of a fight, so, it's reasonable to do the job without having to budget for new discs - I was replacing mine anyway.

    You do need a good drift, say 6 or 8 inches long, 8 to 10 mm in diameter at the tip, with a good unbroken corner, something a bit like this;

    http://buy1.snapon.com/catalog/item.asp?P65=&tool=&item_ID=74199&group_ID=1034&store=uk&dir=catalog

    You don't need to spend a fortune on the dial test indicator and stand - as long as the dial gauge can read down to 0.01mm, it should be OK.

    I found that the washer behind the securing split nut had been damaged/worn (item 38 on the piccie on the link below), but, this was fairly superficial, and a few minutes flatting it on some fine abrasive paper spread over a flat sheet of glass cleaned it up. My concern was to make sure I had a good flat surface, so the end float measurement would be consistent, and not depend upon whether I was hitting a burr, or not.

    http://www.detali.ru/cat/oem_mb2.as...GM=717.433&CT=F&cat=44R&SID=33&SGR=030&SGN=01
     
  7. bigshineybike

    bigshineybike New Member

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    I have just come in from replacing my front wheel bearing and thought i'd make a comment on adjusting bearings without a dial guage
    The pitch of the axle thread is 1mm.
    Assume we tighten the nut firmly finger tight. There may then be some preload on the bearing.
    We do not know how much, there are a lot of parts and they are now all under a bit of tension (stretch) or compression (squeeze).
    One full turn of the axle nut would give something like 1 mm of free play.
    one half turn would be .5mm (half a millimetre)
    To make an angular adjustment on the nut you will need to assume no free play (endfloat) or preload at all.
    Now back off the nut 3.6 degrees (up to 14.4 degrees to stay within MB tolerance) to release the end float to 0.01mm (in my world that's 0.0004 or close to half a thou!)

    I imaging what MB expect of us, is no free play and no preload, which some of us probably are happy to judge by feel alone.
    A garage foreman I worked for 30 years ago used to say
    "Tight's tight and too tight's f***ed"

    I hope I dont appear to be disagreeing with anyone just sharing my thoughts aloud.
     
  8. macabethiel

    macabethiel New Member

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    W124 wheel bearings

    One of my wheel bearings completely failed and was replaced on my old 260E and that was fine a few months earlier. Chap at the Garage said they were prone to sudden failure at very high mileages.

    Mind you it had done 183,000 miles that was on n/s/f , the o/s/f had to be replaced at 187,000 miles. Rears were still original when I sold it on.

    At 190 k having replaced the steering box 12 months earlier I decided to call it day in our 7 year relationship.

    One of the two best Mercs I have ever owned. Not fast, not very economical but stone age technology with overdesign everywhere - just look at those LT leads compared to a Ford or Vauxhall !
     
  9. OP
    OP
    Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    That's the problem - once you've got grease and the friction from the oil seal, I think it's simply impossible to arrive at this happy position by feel alone.

    I think you're right, and I think your point is very perceptive. I've since found some corroborating information in a book quoting German best practice for bearing assembly and setting.

    As a point of interest, did you adjust the bearings by feel or with a gauge?

    I maintain that until you've tried to hit 0.01mm with a gauge, you can't appreciate how difficult and tight the specification actually is.

    This is one of those subjects that invariably causes differences of opinion. Most wheel bearings aren't specified with such a tight tolerance, and so, adjusting by feel is normal practice in most workshops, but incorrect practice with MB front wheel bearings.
     
  10. iscaboy

    iscaboy Hardcore MB Enthusiast

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    It's not that hard, nip it (the nut) up gently, rotate the hub/disk a few turns, back it off, then nip it up by hand (no spanner) again, et voila, no preload and no float.

    No more difficult than a tappet.
     
  11. OP
    OP
    Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    >>It's not that hard

    I would be *amazed* if you could reliably hit the MB specification without a gauge.

    Usually, people who say it isn't difficult are those who have never tried using a gauge to get down to 0.01mm, and so, they really don't know if it's difficult or not.

    Tappet clearances are about 30 times larger than the values involved here - yes!, tappets are easy in comparison!
     
  12. iscaboy

    iscaboy Hardcore MB Enthusiast

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    Helps if you can read specifications.

    MB absolutely will not spec "float 0.01 mm" there is always a tolerance.

    In any event, "feeling" a thou is no big deal, just ask anyone trained on a manual lathe / mill / scraper / etc. Hell, every time you use a micrometer you are "feeling" something of the order of a fiftieth of a thou.

    MB wheel bearings aren't unique on the planet either, "No preload and no float" describes 99.99% of wheel bearings on the planet.

    They'll also slacken off a bit when the whole thing gets up to operating temperature, if you ever have to do these things in places with greater temperature ranges than we have you put in extra float to allow for the low temperatures and thermal contraction.
     
  13. renault12ts

    renault12ts Hardcore MB Enthusiast

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    Duck !!!!
     
    1 person likes this.
  14. OP
    OP
    Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    Here's the spec;

    http://www.ps2cho.net/downloads/MB CD/W124/w124CD2/Program/Chassis/33-0010.pdf

    Yes, there's a tolerance, but, it really doesn't help much.

    I guarantee that you can't feel it by hand.

    By your reply, it's clear that you've never actually tried it.

    >>MB wheel bearings aren't unique on the planet either

    Maybe not, but, there's a clear spec, and a clear method to acheive that. Anything else is guesswork.
     
    1 person likes this.
  15. Will

    Will Hardcore MB Enthusiast

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    Without taking either side on this, I do wonder just how many MBs are running out of 'spec'. I'd hazard a guess that the majority on the roads today will be.

    Reason I suggest this is that I've had several MBs over the years, and the front wheel bearings have been slightly loose on a few of them (in that, there was a noticable level of free-play).

    Despite full MBSH and a modest miles (60k odd at the time of servicing) my CLK55 had slightly loose front wheel bearings on both sides. As did previous W202s (same setup).

    Surely if MB don't check and adjust this at a service (?), after a few thousand miles they'll all be out of spec.

    Didn't have a dial gauge to hand (although I would consider using one if I did :)), but if they're not currently to the nearest 0.00th of a mm they're a damn sight closer than they were, and they're not running tight either.

    Has to be better than doing nothing, as MB seemed to have done.
     
  16. iscaboy

    iscaboy Hardcore MB Enthusiast

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    Like I said, helps if you can read a spec, since you say it doesn't help you much, you obviously can't.

    from the pdf linked.

    Desired end float between 10 and 20 microns.

    Permissible end float 30 microns.

    Permissible radial float 50 microns.

    I guarantee that every turner on the planet can feel that by hand, I also guarantee that every fitter on the planet can feel that by hand, once they have been shown it once.

    I literally can't remember how often I've had to set end float, and even on cheap and easy stuff like vehicle wheel bearings, 4 wheels is a piece of piss, it's a lot more important on a high speed motorcycle.

    You pulled this same **** in the ATF thread, linking to MB documents that CLEARLY stated "SAE ATF" right next to the spec, while claiming that said documents proved ATF was not PAS fluid.

    What you do to your own motor is your lookout.

    When you start giving crap advice to other people with regards to safety critical components it is another kettle of fish entirely.

    I'm NOT trying to start a fight, or an argument, or any of that crap, and due to the nature of the internet there is no way for anyone to tell who knows what, all I'm doing is giving people an alternative set of data.

    Hopefully they will ALL GO AND CHECK WITH A COMPETENT VEHICLE MECHANIC BEFORE TOUCHING THEIR OWN CAR.

    **** up steering, brakes, wheels, etc, even on your own car, and you are liable to both civil and criminal remedies.

    You MOT certificate does not mean ****, it means the vehicle passed the test on that day at that time, AND THAT IS ALL.

    Plod can test your vehicle a week later and determine it unroadworthy, god help you if the cause of that is something that YOU just spannered yourself.
     
    Last edited: Jun 5, 2010
  17. OP
    OP
    Number_Cruncher

    Number_Cruncher Hardcore MB Enthusiast

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    So, you haven't actually done this on a MB? you haven't measured a wheel bearing with a dial gauge and tried to get to this sort of clearance?

    In terms of spec, IF you adjust, you should adjust to between 0.01 and 0.02, any other figure really isn't relevant.

    >>I guarantee that every turner on the planet can feel that by hand,

    You might be able to feel that play when everything is dry, BUT, you can't feel it when there's grease everywhere, and the seal is dragging against it's running surface.

    >>I literally can't remember how often I've had to

    Back to pissing contest tactics?

    I too couldn't count the number of berarings I've fitted and adjusted - however, I was shocked by how difficult it is to meet the MB spec. That's why I tried using a dial gauge, and that's why I've been converted.


    >>You pulled this same **** in the ATF thread, linking to MB documents that CLEARLY stated "SAE ATF" right next to the spec, while claiming that said documents proved ATF was not PAS fluid.

    It's an unusual "ATF" which isn't listed against any MB automatic gearbox, and if PAS fluid were simply ATF, why can't any of the other ATFs listed in MB's spec be used in the PAS. MB's PAS fluid might be ATF in name, but it certainly isn't used as such.



    As for crap advice, all of the tighten by feel, slacken a bit, tap with a hammer, , etc, etc bodging methods are highly subjective and rely on the skill and knowledge of the person doing the adjustment. The use of a dial gauge removes this need for skill and judgement, and makes the work more reliable.


    Now, why all the ****s?

    All I'm suggesting is that people could do no better than follow the *manufacturer's* procedure for setting their wheel bearings. (Just like I was suggesting that people follow MB's spec for which fluid they use in their PAS) I can't see what's so difficult for you?
     
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  18. iscaboy

    iscaboy Hardcore MB Enthusiast

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    You're talking out of your backside mate.

    First off you insist you have to use a dial gauge because you have to set the float to 0.01 mm, then you link to an MB pdf that you apparently can't understand, but when told it says 10 to 20 microns is optimal you change your tune and say you should adjust to BETWEEN 0.01 and 0.02 mm, you then go on to dismiss all other figures as being irrelevant, even the quoted in your linked pdf MB figure of 30 microns.

    You just won't have it that there is any way but the way you do it, and only you are competent to interpret the writings in the holy manuscripts from MB.

    You start talking about a "dial gauge" as though it is some sacred object, but the one's you are talking about are cheap crap, no calibration certificate, and from your avowed position on the impossibility of doing anything by hand you clearly lack even the most rudimentary training in how to use instruments to measure things.

    If you're shocked by how difficult it is to meet MB spec for the wheel bearing, which is by the way pretty much the same spec for any road car, that should tell you about your ability, not the sub angstrom tolerances to which only MB parts are made.

    However, saving the best for last, and I quote

    "The use of a dial gauge removes this need for skill and judgement, and makes the work more reliable."

    This is the singularly most stupid, dangerous and frankly ****ing terrifying thing I have read in many a year.

    Instruments and specialist tools are an ADJUNCT to skill and judgement, NOT A ****ING SUBSTITUTE.

    I'm going to just have to start avoiding threads that you pop up in, life is too ****ing short, you clearly don't want to learn anything.
     
  19. Smiley

    Smiley Hardcore MB Enthusiast

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    Iscaboy,
    NC has provided helpful and useful advice over many years and of course others should work within their own abilities - and of course skill and experience can not be subsituted with a £20 dial gauge - NC never suggested that.
    I am not sure what he has done to upset you but the tone of your posts is unwarranted in my opinion.
     
    1 person likes this.
  20. iscaboy

    iscaboy Hardcore MB Enthusiast

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    Quote, verbatim, the man's own words...

    "The use of a dial gauge removes this need for skill and judgement, and makes the work more reliable."

    end quote.

    You, also, appear to have grave difficulties with the written word.
     

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