Need help with W126 front rotor replacement - PeachParts Mercedes-Benz Forum

francotirador · #1 07-25-2010, 10:14 PM

Quote:

Originally Posted by sixto

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.

Gilly · #2 07-25-2010, 10:19 PM

Quote:

Originally Posted by francotirador

as the rotors are supposed to be changed when the pads are changed.

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

francotirador · #3 07-25-2010, 10:29 PM

Quote:

Originally Posted by Gilly

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

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.

Ferdman · #4 07-26-2010, 05:32 AM

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.

Gilly · #5 07-26-2010, 07:26 AM

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

francotirador · #6 07-26-2010, 08:53 AM

Quote:

Originally Posted by Gilly

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

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.

Hit Man X · #7 07-26-2010, 10:09 AM

You need to purchase some tools to do it properly, most notably a dial indicator with magnetic base. Play is 0.01-0.02mm I think, check the FSM to be certain. It is hardly anything and will take a few tries to get proper.

At the age of these cars, I just replace my wheel bearings. Why? No telling what PO or PO's shops have messed with them before. The seal goes without saying, replace it. There is no excuse not to do so.

An auto company named 'Lisle' makes many odd tools. This is what I use: http://www.lislecorp.com/divisions/products/?product=192 works great.

Just be happy you are smart enough to do them. Most of my 126s had original rotors on the back

francotirador · #8 07-26-2010, 08:50 AM

Quote:

Originally Posted by Ferdman

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.

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