Wheel bearing play... is my Mecedes Manual wrong?
 

I know the recommended procedure people are following for setting front wheel bearing is to use a dial indicator and, with the base on the rotor measure the end play of the spindle. People are recommending half a notch if one's dial indicator is measuring thousands.

My question is that I have a 1977-1988 Mercedes Service Manual for Chassis and Body Series 123. In section 33.3-300/2 it states :

"6 Place tester on front wheel hub and set dial gauge to approx. 2 mm pre-load."

" 7 Check end play of wheel hub by pulling and pushing on flange."

Two millimeters is 0.078".... that's a lot of rattle room. Anyone know what the story is? A typo in my manual?

the manual is saying to pre load the dial to 2mm, THEN to measure the actual tolerance of the bearing...
keep reading for the tolerance, it's not in the instructions for HOW to measure it.

doesn't that translate into looking for 2mm worth of movement?

In any case it is the only measurement I am seeing in the Manual... 2 mm. It certainly is possible I am missing something and that is the point of my question but I don't understand what. I don't know what setting the dial for "2 mm pre-load" means, it is less than clear.

If you go to this link, at the bottom there is a pdf file which is a copy of the manual I am referring to. Step 6 pg 266

Front wheel bearing removal? - Benzworld.org - Mercedes-Benz Discussion Forum

As John suggested above, they are indicating that you need to pre-load the indicator. That way, it can read both positive and negative values. Physically locate your indicator to read 2 mm (or whatever the inch equivalent is) by pushing it slightly against the hub, and then push and pull on it as you mentioned. In your head, you can re-zero the indicator at 2 mm, and then simply read values from there.

Not by a long shot.



The allowable end play is 0.01 - 0.02 mm. (Listed at the very top of page 265 in the service manual.)

qwerty... you found what I was missing. I still don't understand what they are talking about with 2mm pre-load.... unless that means move the dial indicator in (at least) 2mm. There might be a reason to do that. I certainly pushed before I pulled in getting a reading but there it is in black and white, like small print in a legal disclaimer.... Thank you!

The 2mm is nowhere near critical. You just need enough preload on the dial indicator plunger to get a good response. Then you are looking for less than 0.001" of end play.

I follow you... 2mm is not much, is it. Why don't they right "be sure to pre-load the dial gauge so as to not have it bottom out when pushing the flange in and out"

{Simplified version of the below. Hold the Dial Indicator in one Hand so you can see the Dial; put the Plunger in the center of the Palm of the other Hand; push on the Dial Indicator till the pointer moves 2mm; you now have 2mm of preload on the Dial Indicator.}

You have noticed that the Plunger on the Dial Indicator has a Spring that pushes it out.

What preloading the dial Indicator means is that you apply the tip of the Plunger to what you want to measure and then you Push the Body of the Dial Indicator to compress the Plunger 2mm and you lock the indicator in that position.

You either Push the Hub all the way in or all the way out and set the turn the outer Dial on the Indicator to Zero. Then watch the Pointer on the Indicator and push in and pull out on the Hub slowly and watch how far the Pointer moves; that is your actual measurement.

In order for the above to work you need to have a Dial indicator that has enough total movement/Range.

Germans are big on repeatable procedures. They put numbers on EVERYTHING. ;)

On many dial gauges you can rotate the dial face to re-zero the readout after pre-loading. That makes it a bit easier since the accuracy of reading your preload value won't affect the accuracy of your final measurement.

They sure didn't invent documentation that is hard to read and use. My Harbor Freight dial face rotates. I was doing it correctly I just wasn't figuring out how the manual was trying to tell me to do it the way I was doing it.

It is like a lot of things there is a learning curve. Also the translation from German in the Manual also sometimes is not clear or they use words that we would not use.

In somesections of the Manual the Delivery Valve Holder on the Fuel Injection Pumps are called Pipes; confusing because they don't look like Pipes.

I have had Factory manuals for some Japanese car, Toyota and Nissan which were really good. Bentley does stuff for a lot of the German cars but not Mercedes. Haynes manuals can be pretty good but they are sketchy when it comes to Mercedes... In my book the genuine Mercedes manual suck and that's whats so great about the information on this website in particular. I don't think I could own a Benz without it.