Front wheel bearing question
 

RE: my 1995 E320. I have read a lot of the threads concerning getting the bearing free play correct with a dial indicator. No one has addressed what pre-load is. I know what pre-load is regarding suspension. How do you pre-load the dial indicator to 2 mm? I'm using a digital indicator with its magnetic base attached to the hub.
1. Do I need to pre-load a digital gauge?
2. Does the brake disc really need to be removed to measure the .01 to .02 mm? The disc is attached via a set screw directly to the hub.

I replaced the front bearings months ago and obviously didn't do it right. I now got my hands on this digital gauge. This is maddening. I'm following the MB factory manual too. Loosen clamp with 5 mm screw, rotate wheel, tighten clamp, loosen clamp, strike spindle with a dead blow hammer once, then use gauge to adjust. I actually got the free play down to .01/.02 mm. (again, although I didn't pre-load the gauge), the triangular washer just turned the way it should. I then tightened the clamp to 12 Nm. Replaced dust cap, installed wheel, torqued to 110Nm, and I'll be damned, there is still obvious free play in the wheel while rocking the wheel at the 12 o'clock & 6 o'clock positions. What is going on? By the way, the free play isn't in the ball joint.

1/100th of a millimeter is next to nothing, which is what you want. You can achieve this without the dial gage, using the old method of just barely getting the washer to move. If you are close to that, I don't see how you can get obvious freeplay.
See this thread for some more discussion on the topic
http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1409091-how-do-you-use-dial-indicator.html

Mount the dial indicator so the probe has about 2mm movement on the read out. This is normal procedure when using a dial indicator so to answer your question, yes you need to pre-load the indicator.

digital indicator
 

Actually, I don't have to pre-load the indicator - it's digital. I'm the only one on this forum who is using a digital indicator. It's much easier to read .01 or .02 mm than trying to read a hairline on a dial. I simply push the probe up to the hub and lock it in place, then press the "zero" button and it zeros it out for me.

You still need to pre-load it. The probe should never be fully extended when measuring. But why did you ask if you think you know the answer?

Because a day has gone by since I posted that question and spent a few hours playing around with the adjustments, by hand and with the indicator. Since then I figured it out being a digital indicator.

wow,ii have yet to look into replacing my front wheels bearings,what ever happened to the days when you could just remove the lock nut off the spindle remove the rotor and the inner and outer wheel bearing then install a new grease seal,i take it the mercedes is different due to the fact that it is a hub that the rotor mounts onto? id like to investigate mine.

As a 15 year MB mechanic, I've never used a dial indicator to set front wheel bearings. If you're trying to set them that precise, I'll bet you are also setting them too tight.

With pliers, snug the locknut about 1/4 turn past 0 clearance. Back off until it's loose again. By hand, advance the locknut to 0 clearance then back it up ~8mm and lock it.

So you set the bearings with play/clearance of 8mm?

Not 8mm of play. Per duxthe1's procedure turn the locknut by hand to zero clearance then loosen it ~8mm (as measured on the circumference).

Years ago I used to set front wheel bearings on GM cars by lightly snugging up the nut then backing off 1 flat. It's the same idea.

Got it, like a boat trailer.

I thought that the Mercedes ones were supposed to have a pre-load, as in tightened a set amount beyond zero-clearance like the ones on heavy-duty trucks.

I have also heard this too. The wheel bearings are adjusted very tight on a Benz compared to your normal tighten and then back off a bit procedure.

i did mine by hand. so far nothing is burning up in flames.

If you remember that the desired play is between one and two cell (typical round animal or plant cell) diameters, you will probably set it just fine.:book2:

Knowing of course that the bearings sqiush a little when the car's weight goes on them, this would leave clearance all around. The right amount of preload will make everything fit perfectly when loaded, not sloppy like starting out with clearance.