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  #31  
Old 02-21-2009, 12:03 AM
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Thanks for all the replies and intrest in my question. I have read and appreciate every post.

I plan to look for a proper dial indicator. I'm not a machinist, but did have a course in metal working as part of my graduate training in physics - we often have to make or at least spec research equipment. Reading the scale will not be an issue.

IMHO, the MB spec is primarily to be certain the bearing is tight but not under a load. Doing it by feel would probably eliminate the preload but could likely lead to failure from being too loose. I doubt the actual tollerance is that critical as long as it is small and not 0.
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  #32  
Old 02-21-2009, 12:39 AM
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The front wheel bearings on our cars are Set3 and Set5 tapered roller bearings. These are probably the MOST COMMON wheel bearings in the world for rear wheel drive vehicles due to the fact that most GM vehicles used them, in one model or another, for over four DECADES!

These bearings have been adjusted using coconut wrenches in Samoa, ice cubes have been used to set tolerances on them in Nome, political prisoners adjusted them in Siberia using leftover pieces of Russian tanks. These bearings have crossed more continents, without complaint, than a congressman on a tax-payer financed junket.

The fact is,..... Mercedes was ahead of the curve, on a method to set the clearance in a precise manner that could be duplicated. That's all. Most vehicle manufacturers, at the time these bearings were in the greatest use, called for torqueing them down tight to seat them and remove microscopic "burs"; then loosening up the hub/axle nut; then retightening until just barely snug and then backing the nut off a fraction of a turn (amount depending on which service manual you read) (I think Pontiac called for 1/4 or 1/6 of a turn back-off). This eliminated any pre-load, which tapered bearings don't like, yet they were not loose enough to move much and micro-wobble and loosen up (yes, even with the castellated nut/cover and the cotter pin).

Using a dial gauge to set them is the correct way, BUT.......for goodness sake, it doesn't have to be agonized over and over. If you are in range of the Mercedes recommended specs you're "golden" AND THIS IS HOW YOU SHOULD DO IT, WITH THE GAUGE; if you're an old time tech , who has done 1,000 Chevy Impalas, then I'd trust you to do it by feel, and I'd drive from Nome to Patagonia on those bearings.
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  #33  
Old 02-21-2009, 12:42 AM
83240D
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Yeah, you should be fine. I have found that engineers will usually give bonus tolerance on specs. For example, if a part seriously and truly needs a tolerance .002 then he will specify on the blueprint, a tolerance of .0005, knowing that after the parts gets measured by umpteen people, and a common factor of "human error" comes in to play, it will atleast meet HIS true tolerance of .002, and all is well, and birds are singing, the breeze is blowing, people are smiling, and not crashing in a flight to L.A. or something. Listen to this guys.... I make a part for a certain aircraft company that has a tolerance of +/- .0003, My boss took a trip to see these parts and how they are installed. He saw an aerospace worker with a part similar to the one I make, and it was too tight in the hole, so he took a ball peen hammer and nailed that b%tch in. So did the tolerance really matter?
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Its all in perspective guys
jbaj007 is right, get it as close as you can, and your golden.
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  #34  
Old 02-21-2009, 12:48 AM
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Well, I must say this thread I started has been fun to follow. I think the last 3 posts put it all in perspective.

Maybe I'll start a new thread on why MB is so precise with the amount of grease to use in the bearing. This one I know the answer to from experience. Too much grease will actually pull the grease out of the bearing making it run too dry - might even be worse than not enough grease.
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  #35  
Old 02-21-2009, 12:50 AM
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Quote:
Originally Posted by 83240D View Post
Yeah, you should be fine. I have found that engineers will usually give bonus tolerance on specs. For example, if a part seriously and truly needs a tolerance .002 then he will specify on the blueprint, a tolerance of .0005............

If you really knew how little most engineers know about tolerancing and how small .0005" actually is............you'd be amazed.

The reason they specify .0005" is because they can.........not because they are confident that it's absolutely necessary for the component to function. In just about every case, it cannot be necessary for function unless the component is going to operate in a temperature controlled room.

Occasionally we specify .0005" for a tolerance when we want a specific fit to the jet engine part.........it must not assemble at room temperature but must assemble at about 200F. That forces our hand into tolerances of this magnitude.
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  #36  
Old 02-21-2009, 12:57 AM
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Last time I did mine by feel, knowing the proper amount was very small and checked it with a Starrett "last word" indicator, I was at .0009"
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  #37  
Old 02-21-2009, 04:35 AM
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Here's the DIY on the rear bearings. Follow the same basic advice here but use the front tolerance and set everything on the front wheels.

Replacing the rear wheel bearings on a W123, W126

Dave
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  #38  
Old 02-21-2009, 10:34 AM
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Quote:
Originally Posted by jbaj007 View Post
if you're an old time tech , who has done 1,000 Chevy Impalas, then I'd trust you to do it by feel, and I'd drive from Nome to Patagonia on those bearings.
The difference between an Impala and a W123 is the nut. The clamping nut used by MB makes adjustment by "feel" almost impossible. Most domestic cars, on the other hand, use a conventional nut that requires almost no torque to turn until it bottoms.
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