Hello: I recently replaced the rear rotors, calipers, pads and brake hoses on my 1990 300SE. It was suprisingly simple and straightforward. I left the wheel bearings for another day and maybe another person, like a real mechanic. Now I want to tackle the front brakes and change the same items: rotors, calipers, pads and hoses. I've read many posts on the subject and have seen just a few photos. What I'd like to know is if I can change the front rotors without bothering the bearings? I want to be prepared with the proper parts and tools if I have to at least re-pack the bearings. If I do have to remove and re-pack the bearings what will I need besides the correct grease? Seals...? I wouldn't mind replacing the calipers, rotors, pads and hoses myself and then taking the car to a mechanic to properly set the bearings if that's what I have to do.
Thank you in adance for your replies.

Yes, you can replace the front rotors, calipers, brake hoses and brake pads without having to touch the wheel bearings; however, a tech will need to remove each front caliper to remove the rotor/hub assembly in order to replace the inner and outer wheel bearings. So you probably won't save as much money as you expect by doing most of the work yourself.

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Fred Hoelzle

Nope, you can't replace the rotors without having to reset the bearings. Essentially the bearing comes apart as the hub, which the rotor is attached to, comes off the spindle.

Loosening the bolts that hold the rotor to the hub is a major PITA. Heat and a lot of torque are your friends. Some folks reattach the hub to the road wheel when the hub's off the spindle to have something to hold while loosening those bolts.

You should replace the inner bearing seal anytime the hub comes off the spindle. If you don't have service records suggesting the wheel bearings were serviced recently, or at all, plan on cleaning and repacking the wheel bearings. You can't go wrong with MB label green wheel bearing grease and it's conveniently packaged in a front axle's worth quantity.

Sixto
87 300D

Oops, maybe Ferdman knows something I don't. Very possible on a W124. AFAIK, there's no way around it in a W126. I guess we need someone else to chime in.

Sixto
87 300D

Now I see Ferdman's point. You don't have to mess with the outer races when doing the brakes, and the mechanic who does the bearings will essentially do a brake job to get to the bearings. I agree with Ferdman, it makes little sense to make two jobs out of one.

Sixto
87 300D

OK guys, so which one is it? You have me more confused now. I understand that anything a mechanic does later will require removing the caliper and rotor. However, if I can save the wheel bearing job for later and just do the brakes now I would be happy. Besides, any time I've tried to save money by having a mechanic do two or three jobs in one, it has never worked out. They just go to their time schedule book and charge for each individual job.

It's both but mine is an opinion

Here's how the job goes. It's from memory and it's been a few years so check your manual to be sure:

With the caliper out of the way, the rotor is clear for removal. Except, it's bolted to the hub and the bolt heads are on the side of the rotor you can't see. Pry off the grease cap at the center of the hub. Save the bent copper thingy pressed into the center of the spindle. Loosen the bolt pinching the ends of the nut clamp at the end of the spindle. Spin the nut clamp off the spindle. Gently wiggle the rotor and hub on the spindle to loosen the washer and outer bearing roller set. Remove the washer and outer bearing roller set. Pull the rotor and hub off the spindle minding the inner bearing roller set -- it'll likely stay with the hub because of the grease seal but who knows if the grease seal is still intact. Release the rotor from the hub by removing the five bolts holding the rotor to the hub. This is one of the worst jobs I've done on an MB.

Installation is the reverse of removal EXCEPT you have to set bearing preload. Also, if the bearings haven't been repacked in a while, they'll be coated in gray clay rather than green grease. It's up to you to put things back the way they are or give the bearings a good cleaning, inspection and repacking. Whatever you decide, you have to set bearing preload properly or at least close to properly so you don't burn the bearings driving the car to your mechanic. It's not difficult to set preload by feel even without a dial gauge but there's lots of debate whether that's an acceptable method. Lots of mechanics do it by feel but they've done it hundreds of times vs my handful of times and your first time

This assumes Ferdman doesn't in fact know how to remove the rotor without removing the hub. If he knows that secret and is willing to share, everything I wrote means nothing.

Sixto
87 300D

I thank both of you for taking the time to respond. It seems I'll at least need a seal and some MB grease for each side. If anyone else has more to add I'd appreciate it.
My car is very clean and rust free. I haven't had any problems getting anything loose so far. That can certainly change. The procedure does seem to be quite tedious especially since it will have to be done each time the brakes need changing as the rotors are supposed to be changed when the pads are changed.

OK, from a guy who used to do this a lot:
Yes, the rotors on a 126 bolt to the hubs.
The problem with not packing the bearings is that it's really hard to keep junk out of the bearings when you unbolt them (which you are better off getting someone to do with an impact gun rather than by hand). Plus as someone mentioned you "should" replace the inner seal.
There is a few different varieties of bearing packers which make this job somewhat more tolerable. Some are probably cheap enough to just go ahead and buy yourself one, even if it ends up being used on this one job.
Oh, the hub cap can be a bear to remove without the special tool, but again it can be done.
The messy part is getting the old grease out of the hub. Lots of old towels help, or a couple rolls of paper towels.
If you have someone who can zing the old rotors off and new ones on, it's not that bad of a job.
We (or at least I) can talk you through setting the bearings.
Bearing grease, just use a name brand high temp bearing grease. Geez lets not turn this into an "oil thread"!.
Gilly

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Not true, in most cases and normal brake useage, you usually will end up doing the rotors every other time on the front and even less seldomly on the rear, and NEVER have the rotors machined when replacing pads, just-replace-the-pads.....
Gilly

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Thanks for your input. I don't mind the cost of new rotors. The rear brake job had to be about as easy as it gets to replace the rotors, calipers...
The front doesn't sound like fun, but with the right guidance I can get it done. I don't mind getting dirty and I can certainly clean the bearings as they should be. I'd like to replace them all, but I just don't want to do it now. Maybe I can just clean and repack everything now and replace it all later.

I apologize for any confusion I caused. My experience is with 124 cars and before I replied I looked quickly at an online parts website to check the appearance of 126 front rotors. At a glance they appeared the same as 124 rotors so I responded accordingly. Apparently working on 126 front rotors is much more difficult.

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Fred Hoelzle

Pretty rare to have to replace the bearings. The cages will notmally be somewhat loose of course, but if a cage would be so loose as to make you worry about the bearing coming uncaged in your hands, or if you see a lot of discoloration (blueing) of the individual rollers or they are pitted, then you should probably "issue a stop-work" and do the bearings. But again highly unusual and unlikely.
Also examine the races for any signs of scoring of course.
Gilly

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Hey, no problem. Maybe I need to get a 124 next time.
Thank you.

Well, I'm going to give it a try. I have to learn sometime. Hopefully this isn't the last W126 I own. I just want to make sure I have everything here when I do the job. I hate having to run out in the middle of working on the car. And even worse than that is finding that it takes a day or two to get parts that are not in stock, which is most everything.
Thank you.