W124 wheel bearing re-grease

[maxypriest]

I'm all up for preventitive maintence.

My front wheel bearings need a little adjustment, so i was thinking i'll re grease them at the same time.

Worth doing?

Any advise?

Max

 

[Number_Cruncher]

If and only if you can regrease in clean conditions. If you introduce any dirt, you'll make things worse, not better.

You'll need a dial gaue to set the bearings up properly.

 

[television]

Technically a dial gauge is used to check the pre load on the bearings, the bearings are not being replaced in this case, and satisfactory results can be got by just tightening up a touch, good results can be had by spinning the hub as you tighten, when you start to feel the hub harder to turn, back off the nut by a 1/4 turn and this does in practice equal the 0.05mm limit allowed, the pre load figure is 2mm

 

[Number_Cruncher]

Sorry Malcolm, I can't agree with your post.

The front wheel bearings aren't pre-loaded at all - they *must* have a running clearance.

The difficulty is that the clearance, as psecified by MB, is very very small. You can't get *anywhere* near setting this clearance by any other method than by the use of a dial gauge.

Edit: Having consulted the MB spec, I can see how Malcolm has arrived at what he has written.

To clarify;

2mm preload is *NOT* setting the preload for the bearing - it's to set the dial gauge with 2mm of preload.

0.05mm is the maximum allowed when checking an in-situ bearing - this figure is *not* applicable in this case.

Play between 0.01 and 0.02mm is how you should set the bearing after disturbing the clamping nut. These are the applicable setting figures in this case. There's absolutely no way you can set this without a dial gauge.

 

[maxypriest]

Ok.... can of worms here!

So where do i attach the magnetic base, and where does the tip of the gauge touch?

Cheers!

Max

 

[Number_Cruncher]

The magnetic base attaches to the flat face of the hub, where the bolt holes are, and the probe of the dial gauge touches onto the nose of the axle/spindle. To assess the play, you pull and push the hub while watching the needle on the gauge.

If you don't already have a dial gauge, there's no need to spend a great amount in buying one - they aren't expensive.

 

[television]

We could make every thread and post so technical that there would be no use for a forum at all, in practice 100s have tightened the bearings up a touch with no come back what so ever, and that must be better than doing nothing.

Rightly or wrongly I have changed some 100 wheel bearings in my life without a dial gauge, just using my engineering experience, never had one go wrong, and never a failure mentioned on here with any advice or info that I have given

 

[Number_Cruncher]

I don't doubt it Malcolm - I too have fitted many bearings on many different vehcles without a dial gauge, and without a problem.

However, this was before I became aware of the MB specification for their front wheel bearings. This bearing setting method and clearance value has been in place since at least W123, and probably goes back even further - it's not a new or sudden change in spec.

When I renewed the front wheel bearing on my W124, I played around a bit with setting the clearance, because I didn't quite believe you had to use a DTI, but when you begin to get close to the MB spec, you can no longer feel the play by hand. So, if you can feel play, it's too loose. As you can't feel the play be hand, you are in danger of over-tightening, hence you are forced to measure it, and hence, use a dial gauge.

In the case of these wheel bearings, the special kit required isn't expensive or difficult to use. I see no reason to bodge, and I see no reason to deviate from the MB spec, nor to advise others to deviate from the spec.

 

[antijam]

I was wondering how you know your wheel bearings need adjustment?

If there is excessive play of the wheel on the stub axle, by the time you realise this very often the bearings are already in need of replacement. If you can hear a problem, then new bearings are essential.

Assuming they are still OK and you do a regrease, I have to agree with Malcolm - tighten up until free rotation is just seen to bind and then back off one quarter turn.

While the dial gauge theoretically guarantees the desired axial play, they are not always that easy to use in practise. A rigid anchor for the base is essential and with a newly greased bearing the 'stickiness' of the grease can make it difficult to accurately sense the end float.

 

[Number_Cruncher]

>>the 'stickiness' of the grease can make it difficult to accurately sense the end float.

Yes! That's actually part of the argument for having to use a dial gauge. There's no way you can feel the clearance by hand.

>>tighten up until free rotation is just seen to bind and then back off one quarter turn.

This will always leave these bearings WAY too loose. If you can feel any clearance at all, these bearings are too loose.

I challenge anyone to set these bearings up by hand, and then check with a dial gauge. I guarantee when you measure, you'll be outside the 0.01 to 0.02 adjustment spec.

Until you've tried both methods back to back, you will not believe just how inaccurate, imprecise and variable the rule of thumb methods are.

 

[television]

We are talking about 20 year old car that have done up to say 200k miles and the bearings have never been adjusted.

As antijam, one just cant go and buy a dial gauge and be an expert in 5 mins.

I guarantee that if you just do up the nut till resistance is felt, and back off 1/4 turn that will be very close, and not too tight,but 100 times better than it was before, you could work it out from the pitch of the stub axle thread.
If the pitch say is 1mm per turn, one 1/4 turn is 0.25 more than enough to make it better, but not so tight as to cause any damage

One does have to be a little practical at times, or these cars would all be thrown away if special tools had to be bought for every job

 

[kth286]

Another item that can affect the feel is the brake pad.

If your wheel bearing was slack and you now tighten the nut it will move the disc brake towards the inside pad as the gap is very small when pads release after a braking action.

You may feel that it is the bearing that is binding, and that would be wrong.

So, move the pads apart from the disc before making wheel bearing adjustment.

 

[Number_Cruncher]

>>I guarantee that if you just do up the nut till resistance is felt, and back off 1/4 turn that will be very close

That can only have been written by someone who has never actually measured it.

0.01mm is 4 tenths of a thou - it's truly tiny.

A dial gauge and stand isn't at all expensive.

I find it odd to read all this advocation of deviation from the MB specs which are usually liberally quoted and distributed.

 

[television]

Have a nice day

 

[S80]

I must admit to having a foot in both Number_Cruncher and Television's 'camp'

As an Engineer, I tend to look for precise, numerical methods of problem-solving and repair, but sometimes these must yield to practical constraints - be they lack of specialist tools, working environment, money....

Quite often, I feel that the procedures given in workshop manuals attempt to remove much of the variability which would otherwise result from using - for example - expressions such as 'finger tight' or 'until resistance is felt'. Peoples' sensitivity (and sensitivities!) varies enormously, and what is perceived as 'finger-tight' by the seven-stone weakling will not appear so to a twenty-stone 'gorilla'.

So for adjusting taper-roller wheel bearings, there will be a large variation in what is meant by 'just perceptible endfloat'. People with good mechanical 'sympathy' - gained through experience and/or a natural aptitude will, I'd guess', get pretty close to an acceptable adjustment without recourse to a DTI. However, as Number_Cruncher points out, such gauges are easily obtained for relatively little cost.

As a further example, I would cite doing a cylinder head removal as an example where 'perfection' is rarely practised by the DIY-er. Checking the head for surface flatness is easy to do - just take it along to your friendly engine rebuilder. But what about the block? Just removing all traces of the old gasket without bits getting where they shouldn't can be a right pain in the proverbial - never mind messing about with straight-edges or sheets of glass. Sure, you could remove the entire engine, dismantle it and take the block to that engine rebuilders for a surface check and 'boil wash' while they're at it - but that's getting into the realms of fantasy for most.

However, as the French would say, 'that's all very well in practice, but does it work in theory?'

 

[roofless]

a very good debate but any chance you could make them a bit shorter & by the way no need for calibration just not as long :lol:

 

[Rory]

0.01mm is 4 tenths of a thou - it's truly tiny.

I was thinking that while reading the thread - surely you could move it 0.01mm depending on how hard you tried to move the hub?


Must admit that I've always been slightly nervous setting wheel bearing, and a young lad caused a fatal crash in the South West by doing them wrong on his Golf.

 

[Xtractorfan]

The method as detailed by Malcolm has been the norm for many, many years for adjusting bearings, and used by the guys who knew what they were doing, and I bet as well, done in many MB workshops,.... there were and still are those who will tighten up to recommended torques and follow the written word religiously, Ask me whom I would rather fit my 'new' or adjust my wheel bearings...The young apprentice with the dial gauge or the seasoned mechanic who could feel if a wheel bearing was properly torqued..

As S80 above and his wise scribblings, there is a place for both, My only problem with Number crunchers by the book method is the fact that a lot of DIYers wouldnt even know what a dial guage looked like...

 

[television]

On most of my post I try and talk in a language so that those who have not had any engineering background can feel confident in doing some of these jobs.

On the electric front I could tell folk to get an oscilloscope and start putting up wave forms, but to understand what you are looking at takes some training, even a simple dial gauge does take some practice.

 

[Number_Cruncher]

>>The method as detailed by Malcolm has been the norm for many, many years for adjusting bearings

That's quite right, and I've done this myself on many many bearings, on cars, buses, trucks, tractors over the years - but, the method doesn't get anywhere near setting up an MB bearing correctly.

If I were daft enough to pay someone to work on my car, I wouldn't be happy paying for anything other than correct parts, fitted using correct procedures.

IF these bearings could be set by feel, and IF dial gauges were expensive, and IF they were difficult to use, I could understand the desire to deviate from Mercedes' carefully written specification.

I don't understand why people are so keen to bodge wheel bearings, but will talk about polishing under their wheel arches, and the chrome finish of their wheel bolts.

Here's an interesting snippet of a thread on a US forum - please note the name of the author.

--------------8<-------------


Front Wheel Bearing W126
Stu Ritter
Tue Apr 15 16:17:04 MDT 2003
--------------------------------------------------------------

Wray Stanley wrote:

> Scott,
>
> The bearing tolerance is so small that I don't believe anyone who says they can "feel" when it is
> right. Dial indicator is mandatory.

Or, let's put it this way.
Every mechanic who has ever come to work for me, and in 25 years of
owning a shop I'd say I've had 8 or 9, has been put to the test because
none of them would believe me when I told them they couldn't set a wheel
bearing by hand. They would poopah me. OK, we would get a car, and
I would have them set the bearings. Both sides, so we could average their
mistakes. Then we would hook up a dial and measure it. None of them, not
a one of them got them to within 5 thou, much less the .01 - .02mm required.
All were set way to loose, as mechanics are wont to do. That was all it
took. After that, they all used the dial. It takes about 1 minute to hook it up
and put it away so they had no excuses.

Stu

--------------8<-------------

Now, these mechanics working for Mr Ritter were all at least an order of magnitude wrong in their setting - that's not even close!!

I do recognise that some intelligence is needed to use the dial gauge method - but that intelligence is not directly related to the use of or reading of the gauge - as mentioned by Rory, you can flex the hub enough to give 0.01mm deflection of the needle, and so, you need to distiguish between the sudden jump as play is taken up, and the more proportional response you obtain as the hub flexes.

If someone can't use and read a dial gauge, then, they must be seriously lacking in the brain department - it's no more difficult than reading the hands on a wall clock.

There is a place for pragmatism in the face of expensive special tools, or for needlessly difficult and nugatory procedures, but, I really do not think that this is one of them.