Will bearing failure be visible by visual inspection of bearings?(1985 300D)
I am starting to hear that grumbling noise when a wheel bearing goes bad, and I am skeptical because I replaced them with OEM bearings.
I am pretty sure I did the job correctly.
I am going to pull the rotors tonight. I am just curious.
Will bearing failure be visible by visual inspection? Or can it escape even the trained eye?

Also failed bearings have a characteristic noise. Can I be confusing this noise with tire noise? I had to drive the car for several weeks on blown shocks.

Does the sound get louder when you corner? I had a wheel bearing do this and couldn't find any imperfection until I cut it apart. There was a very small mark on the innner roller surface.

If you remove the bearing and wash them you will see if there is any problem with the cup or bearing.. The bearing has a O on the large end.. it is the wear bar.. if its worn flat then the bearing was over tightened or just worn out.. The most common thing on the rear bearings is to over tighten them and burn them up.. However when you remove the rear bearings in most cases you damage them so they will need replaced ... You can check them by checking the end play.. They should have about 2 thousands end play.. perhaps up to 4 but not much more.. however you should have checked for that when you put them in.. There are also a number of other things that will cause noises on corners.. so if the end play is right I would just leave them and check them from time to time.. If it does grow a lot it will mean it has a bad bearing..

Ken

I recently replaced my front bearings and everything sounded fine until the dreaded grumbling began to eminate from the left passenger wheel. I changed my pads and the sound went away. Later the sound emerged. Upon arriving home, I took a look at the left front wheel and noticed a broken lugbolt just hanging out!
My wheels have spacers which must have affected the load placed on the bolts. Other members advised that the wheels need to be centered by the hub, not the bolts. If you have spacers, try removing them and see if this rectifies your situation. I was unable to remove the broken bolt with an EZ-out so now it's to the junkyard for another hub

anyways, good luck with the car.

Carrameow,

Rolling element bearing failures generally result from conditions that cause the lubricant to fail first. The most common causes are being too tight or too loose. Too tight causes low oil film thickness, leading to heating that thins the film thickness more, leading to heating and so on until the grease is destroyed and the bearing gets real hot and siezes. This process is known as thermal runaway. That will be very visually apparent. The grease will stink and the race will be discolored if you get to the bearing before it siezes. If not, well.....

Too loose leads to a phenonmena called ball skid. Rather than roll the balls skid, as the name implies, and a normal oil film does not form. The metal to metal skidding damages the balls and the races, but you do not get rapid thermal problems leading to siezing in a short time. Ball skidding will eventually ruin the lubricant, and the surface finish on the races and balls. Metal to metal contact generates wear particles that have no where to go, so they end up being run over by the balls, causing what start out to be microscopic dents. Eventually the race gets a frosted line where the ball contact is, which, under magnification is a line of surface defects. Left in, the bearing will eventually form pits and craters in these areas as the surface defects grow into visible to the naked eye type events. The balls may or may not show signs of distress, since they present an infinite number of surface tracks to the race and the microscopic stuff is kind of evenly distributed over the surface of the balls. The race sees every ball run by over the same contact line, so it suffers more from this problem in most cases.

Another very popular failure mode results from a lack of cleanliness during the bearing installation. In this case you may have the pre-load correct and be neither too tight or too loose. But the dirt starts the denting and defect generating process as soon as you get moving. Dents and bumps also disrupt the oil film between the ball and race, leading to metal to metal contact. With no place for the stuff to go, it is not long before the degrading bearing begins to add wear and particles from other damage and the race begins to look a lot like the bearing without sufficient pre-load. Under a microscope they look a bit different, but ultimately the failure mode is similar.

There is a lot more to the subject, and I hope I have not oversimplified to the point of misleading you. But the answer to your question is yes. If the bearing is bad enough to make audible noise during normal operation, the damage should be visible. Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Wheel bearings, when new, are bright and shiny, both rollers and races. Any wear, scratches, roughness, or, worst, divots out of the races, will cause some noise.

Short of pulling the hub, you can jack up and pull the pads out of the calipers. That eliminates brake noise. Check play -- if you can move the hub straight in and out, the bearings will growl as the hub vibrates, they are too loose.

Then rotate the hub. Should turn smoothly with minimal noise -- you may feel some minor vibration or a hiss as the grease moves around, but no growling, tight spots, or crunching noises.

I've seen bearings set so tight that the manufactures marks on the inner race were clearly imprinted on the thrust washer! Too tight cold and they REALLY get tight as they head up and the hub doesn't, you can ruin them in less than 100 miles.

Ditto for dirt in the grease, too -- or salt from driving through a salty slush puddle with warm bearings. Did this in Canada -- the retainer ring ran through the rollers, believe it or not, without the wheel falling off. Had to buy a new stub axle, the bearing was welded on!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!