How much do you tighten front wheel bearings? - PeachParts Mercedes-Benz Forum

Diesel Dan · #1 10-01-2006, 06:19 PM

Hey folks,
I'm finishing up a front brake job on my '87 300D, and I decided to repack the outer bearings while I was in there. Can someone tell me the best way to tighten the outer nut (the one that's split with the allen bolt) that holds the bearing? How do you know how tight/loose to make it? What is the procedure? Thanks!

PatricdeBoer · #2 10-01-2006, 07:23 PM

I think you need a dial indicator to get it perfect. I usually tighten it until there is resistance when you spin the hub, then back off a little bit.

bjcsc · #3 10-01-2006, 07:29 PM

Dan:
The procedure is to tighten the nut while turning the wheel. Tighten it until you can't turn the wheel anymore with moderate force. Then, back the nut off 120 degrees (1/3 turn), give the end of the stub a good smack with a hammer and then tighten the allen bolt.

nhdoc · #4 10-01-2006, 10:26 PM

Mercedes has a spec for runout which would require a dial indicator...having said that I have never used one to set bearings and have done them as a prior poster has said...tighten until you feel resistance when trying to spin the hub then back off until it spins freely but before and real lateral play is felt.

Mechanics usually grab the nut with a pair of water pump pliers and spin the hub with one hand while they twist the nut with the pliers to feel the resistance...back and forth, back and forth while it spins...then when it is "just right" they set it with the lock and it's done.

I believe the spec is something like .001" and most american cars use a castle nut/cotter pin that is much less precise than the MB with the locking nut is.

Brian Carlton · #5 10-01-2006, 10:34 PM

The spec is .0005".

The problem is that you can't feel .0005" and all of the previous advice leaves you with no good idea of how much free play you have.

The danger in this approach is the fact that tapered roller bearings will quickly destroy themselves if they have a preload. All of the aforementioned procedures can result in preload.

So, without a dial indicator, you must back off the nut until you feel the slightest bit of axial play in the rotor. If you hear it clunk, you've got way too much. Just the very slightest bump with the force from pulling on it is what you're looking for. In reality, this amount of clearance is too much, but, without a dial indicator, it's far more preferable to a preload (pressure on the bearing rollers).

dkveuro · #6 10-01-2006, 10:56 PM

Somebody just came up with a self adjusting wheel bearing kit....anyone know who it was ? Has a spring loaded nut and thrust assembly dohickey.

FOUND IT !!!http://www.coatesengine.com/eGallery/pages/wheelbearing.htm

or........ http://www.coatesengine.com/photo_gallery.html

.

Diesel Dan · #7 10-01-2006, 11:47 PM

Thanks to all for the advice. I've thought on several occasions of getting a dial indicator, but just never felt I could justify it, considering the number of times I would use it.

Without the benefit of the indicator, BJCSC's advice sounds the most scientific so far, and my method in the past has been similar to what the other responders have said, so I think I'll try both ways and see where the nut ends up each time.

My method has been to yank back and forth on the hub while tightening until I no longer hear any clunking, or feel movement, and mentally take note of that spot. Then tighten until I feel resistence. Then back off to a point in between these two points. Hopefully, this method, and BJCSC's method will end up in the same spot! Then I'd feel really reassured!

Brian Carlton · #8 10-02-2006, 12:43 AM

Quote:

Originally Posted by Diesel Dan

My method has been to yank back and forth on the hub while tightening until I no longer hear any clunking, or feel movement, and mentally take note of that spot. Then tighten until I feel resistence. Then back off to a point in between these two points.

This procedure will guarantee you a preload and the bearings will fail prematurely. Use it at your peril.

Diesel Dan · #9 10-02-2006, 01:06 AM

Quote:

Originally Posted by Brian Carlton

This procedure will guarantee you a preload and the bearings will fail prematurely. Use it at your peril.

Sounds like you think I should err on the side of too loose rather than too tight. If I'm yanking back and forth and no longer feel any movement, or hear any clunk whatsoever, then you think that is too tight already?

As I read your first post again, it seems you think there should actually be a slight bit of play, a slight clunk, or "bump" as you put it?

Anyone dispute this approach? If not, then I'll tighten until just a hair before I no longer hear/feel lateral movement.

#10 10-02-2006, 01:10 AM

They need clearance to expand as they get warm.

Brian Carlton · #11 10-02-2006, 01:13 AM

Quote:

Originally Posted by Diesel Dan

If not, then I'll tighten until just a hair before I no longer hear/feel lateral movement.

Exactly.

Better to overtighten them and spin the wheel to make sure the hub is seated..........then back off the nut and tighten until just before you no longer feel any axial movement. Even this is too much clearance, but, it's better than the alternative.

#12 10-02-2006, 01:18 AM

FWIW, here is the manual section:

http://mb.braingears.com/123_DISK2/program/Chassis/33-300.pdf