Mercedes-Benz Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
651 Posts
Discussion Starter #1
What is the life expectancy of our W140 Rear Wheel Bearings. I ask since at 215K miles am I on borrowed time or do most never fail. If you have any relevant info please pass it on.

For example if I told you that my vehicle had 170K miles and was asking the same question about the Water Pump I would expect the response to be "at 170K miles you are on borrowed time with the water pump since they generally fail at about 150K miles"

Thanks,

Seth
 

·
Registered
Joined
·
3,569 Posts
when i was student of mechanical engineering we were taught that such bearings are designed for at least 10,000 hours of work under predicted load. i would say that your load is much under the predicted because i guess you do not drive with maximal speed and with maximal weight in the trunk. In my mind this fact is somehow compensated with age of bearings; the fat is most probably going out of the bearings, etc.

an example: 2 hours of driving per day is 700 hours per year. this gives 15 years of lifespan for the wheel bearings. i guess this means ca. 1 million of kilometers if your average speed is 100 km/h.

all this is a rough estimation of course if you ask me.
 

·
Registered
Joined
·
405 Posts
I dont think there is a true number given there are so many factors, one side may outlive another by a fair distance.

Replace them when they are needed unless you don't mind spending money, its an expensive exercise and time consuming or both. When they start to go bad you will hear it and they will become so loud you couldn't ignore. They rarely develop play before being replaced so they aren't so critical like a water pump which can completely fail in a short period maybe taking things with it.

I replaced mine at 228,000 km because i had the axle off, they were a little rough but probably would of lasted a very long time in that state given they are sealed bearings. My car is appeared a little quieter after replacement but it could of been placebo.
 

·
Registered
Joined
·
3,569 Posts
I dont think there is a true number given there are so many factors, one side may outlive another by a fair distance.
actually 10,000 hours is a very true number :).

more precisely: at least 10,000 hours if working conditions are not worse than the predicted conditions.

of course this is true in let's say 99% of real situations (I forgot the exact number).
 

·
Registered
Joined
·
405 Posts
Im not doubting the number for a theoretic estimate but you said it yourself about predicted conditions, i don't believe real world data exists in this case for a honest figure.
 

·
Registered
Joined
·
3,569 Posts
ok,i will try once again :):

10,000 hours is a minimal life expectancy in close to 100% of all cases. In reality it is not 100% but somewhere between 95 - 99% I guess.

So in most cases this type of bearings will survive at least 10,000 hours of work. The only note is that working conditions must not exceed the predicted ones, however this is not a case if the user of a car does not exhibit abnormal actions. Normal driving (not faster than 250 km/h, not more load than 2,500 kg, normal braking, normal driving through curves, etc) is just normal driving, so a way of driving for which the car was made.

I only admit that the above explanation does not consider the age of the bearing, but once again, as an engineer, I would say that these cars are driven much much much below the designed conditions, so this can be compensated with the age of the bearings.

A lot of people consider statistics as a mother of lies but in top science it is not so. Statistics is actually 100% right. Not 99,99% but 100,00% ! Why? Because there are another parameters and variables, not only mean values, etc. One of them is confidence level for instance. Statistics always considers possibility that some phenomenon will not happen (or it will); bearing life expectancy is a typical case of a NORMAL (so natural) phenomenon for which a Gaussian distribution of values and standard deviations is significant. In this type of distribution everything is nicely defined, so consequently life expectancy for a big number of bearings (population) can be predicted ... of course with limited confidence level which is usually 1-5 % in mechanical engineering. So if you are referring to this 1 -5% then yes, you are right ... of course, exceptions are typical for all natural phenomena. But 1-5% is a pretty high confidence level.
 

·
Premium Member
Joined
·
738 Posts
Mechanical Engineering 101

Samo,

Well stated on the simple basics of Mechanical Engineering design of mechanical elements such as bearings.

It is common in industries such as power generation and paper making, that bearings and other mechanical equipment are changed before the expected failure. This is called predictive maintenance. This is simply because the failure of that "Cheap" bearing could create a multimillion dollar loss in production down time. For example, in a power plant during an outage (shutdown), bearings are routinely examined for wear and replaced or rolled as necessary. They do not have the outage to replace the bearings, but while they are down, they examine them.

In the days before a single serpentine belt we had multiple belts on the front of our cars. If you changed the one in back, you also changed the others since they were already off. If you remove or replace the engine, you always replace the motor mounts.

So, the short answer regarding the bearings in the rear of our star cars is, "if they ain't broke don't fix em". If you have the rear end disassembled and your car has high mileage, then change the bearings while you are there. :nerd
 

·
Registered
Joined
·
405 Posts
Well if what you say is indeed accurate then i've replaced more of what are presumably factory wheel bearings than i can remember in your 1-5% range, most of these cars less than 300,000km. We must have bad luck in this country.
 

·
Registered
Joined
·
3,569 Posts
NZJay, the original question was about life expectancy. I offered an answer which tells how to roughly predict it. My rear wheel bearings have 425,000 km and they seem to be fine. During doing brakes I can feel smooth operation only so far. So my message was that bearings are designed to survive a specific amount of time in predicted conditions during their exploitation. I really think most of people do not know this fact.

we are just chatting here. In addition, I actually did not claim that rear bearings for W140 specifically should survive 1,000,000 km. So maybe for our cars this limit is 5,000 hours or 500,000 km (or more ... who knows). But the 'story" is always the same: bearing X will survive at least Y hours in normal conditions of exploitation. if this is not true, then this can happen only in let's say Z% (e.g., 5%) of real cases.

In mechanical engineering there are specific tools for estimating bearings health. The measurement of vibrations on the bearing or near it can tell how worn it is. Wavelet analysis and cepstrum analysis are two of extremely powerful tools in this area. Everybody who has a decent A/D converter, accelerometer, and some knowledge about digital signals can try this at home (google.com).

NZJay, actually your comments are closer to reality than my comments from practical point of view :).
 

·
Registered
Joined
·
3,569 Posts
this is a good info (page 6):

Market demands for commercial vehicles (CVs) have progressed from a mileage of 300,000 km with standard bearings to more than a million km with wheel bearing units.
 

Attachments

·
Premium Member
Joined
·
738 Posts
this is a good info (page 6):

Market demands for commercial vehicles (CVs) have progressed from a mileage of 300,000 km with standard bearings to more than a million km with wheel bearing units.
Samo,

Don't give away all of our secrets, they won't need us MEs any more!:devil
 

·
Registered
Joined
·
3,569 Posts
David, do not worry, fortunately they will need us more than ever. New generations are extremely good in handling ipads and iphones, however I think creativeness, one's own initiative and inventiveness is not something which is better now than in our times ... maybe it is even worse. Good for us.
 

·
Registered
Joined
·
405 Posts
These plastic idler\tensioner pulleys\bearings are the main issue i have these days, they are expensive to replace here and have terrible service life compared to a metal pulley with easily obtainable and quality replacement 6203 etc bearing which you just knock out and in. Euro brands seems to be the worst for this given their love for recycled plastics.
 

·
Registered
Joined
·
3,569 Posts
yes, many times i do not have any reasonable explanation why some parts are made of plastics. The only one is money (profit) of course. To some degree the weight, too.
 

·
Registered
Joined
·
651 Posts
Discussion Starter #16
NZJay

In the future you are better off with your time and $$$ using INA which are OEM for the pulley of idler and tensioner. I would suggest avoiding Uro for anything as they are cheap (for a reason) chinese parts.

Seth
 

·
Registered
Joined
·
405 Posts
I agree but was running a new INA idler pulley and new SKF bearing in the tensioner in my old S600, only URO part ive used in my life was a fan clutch while i found a better replacement. The INA idler in W140 is much better design than say the INA BMW idler
Ive had heaps of plastic INA pulleys on BMW's and they dont last long before coming noisy(never used one till failure). Ive just put in a Gates idler with C&P bearing for a trial run in the BMW so will see if that preforms any better.

I think the grease they use in them appears like EP grease instead of high temp wheel bearing grease, they also appear under greased and the seals fail easy misting out the grease ( possibly due to the plastic distorting over time). Never had those issue in a proper sealed metal cased bearing. Its just cost cutting.
 

·
Premium Member
Joined
·
738 Posts
NZJay

In the future you are better off with your time and $$$ using INA which are OEM for the pulley of idler and tensioner. I would suggest avoiding Uro for anything as they are cheap (for a reason) chinese parts.

Seth
I have learned the hard way about the URO Crap.:thumbsup:
 
1 - 18 of 18 Posts
About this Discussion
17 Replies
4 Participants
quakercity
Mercedes-Benz Forum
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!
Full Forum Listing
Top