How To Replace Front Rotor W123 - PeachParts Mercedes-Benz Forum

rhodes2010 · #1 02-19-2008, 03:31 AM

I replaced both front rotors on my 1980 300D W123 this weekend.

I photographed the key points but fear the file size limit on the board
may keep me from getting them loaded.

My original rotors had grown very very thin, and then cracked.
The car has 300,000 so I suppose it is to be expected.

I had purchased the Brembo rotors prior to this so was pretty much ready.
I purchased inner bearings BR5 and inner seal 19630 and outer bearing BR3 from Kragen online for $44 (both sides, all six boxes).
I put all the bearing boxes in the freezer as soon as I got them home.
Also purchased some Blue Threadlock.

After going through the learning curve on the left side the right side took
no more than 3 hours start to finish.

My biggest grief was all the old grease and the half roll of paper towels it
took to clean it all off.

The steps:
1. lift car and remove wheel.
2. Use 19mm breaker bar and then ratchet to remove 2 caliper bolts
and remove caliper.
3. remove grease cap over center of hub.
4. Use 5mm allen/hex wrench to loosen nut on spindle.
5. remove spindle nut and slide rotor off of spindle.
6. Remove inner and outer bearing races with a punch and hammer.
7. Clean grease from inside of hub.
8. Remove hub from rotor with 8mm allen/hex that was 3/8 drive adapted to a
1/2 inch breaker bar and using a piece of steel tube for leverage.
For this I bolted the hub to the wheel with 3 nuts and had someone stand
on the inside edge of tire while I broke each of the five bolts loose.
9. Cleaned the five removed bolts with a wire brush.
10. Cleaned off the mounting surface of hub with brake cleaner and positioned
new rotor. Used blue threadlock sparingly and threaded the allen bolts
back into hub.
11. Torqued allen bolts to 80 - 85 pounds.
12. Removed hub/rotor from wheel.
13. Went to freezer and got bearings and seal and installed inner and outer
race with hammer and punch, gently but firmly.
14. Packed inner bearing using grease gun and bearing packer and installed
into greased race.
15. Wiped grease on inside of seal and installed inner seal with hammer, gently
but firmly.
16. Cleaned old grease off of spindle and wiped new grease on base of spindle
where the seal will ride.
17. Use brake cleaner to clean inside of rotor, wipe very clean.
18. Slid rotor and hub onto spindle until seated.
19. Packed inside of hub with grease from grease gun, not too much.
20. Packed outer bearing with grease using bearing packer and grease gun.
21. Placed outer bearing into hub and installed spindle nut.
22. Tightened spindle nut down hard using channel locks to turn it as far as
I could then backed off no more than 1/3 turn.
23. Checked smooth spin of rotor, there should be no binding and certainly
no looseness felt when rotor is pulled or flexed.
24. When satisfied I tightened 5mm allen bolt on spindle nut tight.
25. Put some grease around spindle nut and a little inside grease cap
then installed grease cap over hub.
26. Reinstalled caliper onto new rotor. This can be tricky. Use new pads
if possible and spread pads far enough to accommodate new rotor thickness.
27. Added some blue threadlock to caliper bolts and reinstalled.

Got back in drivers seat , started engine and gently pumped brakes back up until firm.
Took a few short test drives and listened carefully for noise like bearings or rotor-to-caliper interference.
All was good.

In a few weeks I will install new upper and lower ball joints and tie rods.
This has never been done and the boots are finally cracked and the joints dry.

Please comment with corrections that should be made to the above,
we do not want to give out wrong information on something as critical as
front end components.

rhodes2010 · #2 02-19-2008, 03:37 AM

The first two pictures are removal of cap and the crack in rotor.

Here are Loosen nut and remove bearing race.

rhodes2010 · #3 02-19-2008, 03:41 AM

The 1/2 inch breaker bar with 8mm hex attached.

The breaker bar with some leverage. Have someone stand on the tire.

Wire brush to clean the bolts, and some blue threadlock to reinstall.

rhodes2010 · #4 02-19-2008, 03:45 AM

Torque the hub and install the inner and outer race
that have been in the freezer for a few hours.

rhodes2010 · #5 02-19-2008, 03:49 AM

I used a manual grease gun to pack the bearings.

We used to do this by hand. I can't say this is less messy, you still get a lot of grease on your hands.

mobetta · #6 02-19-2008, 03:26 PM

nice post. The only thing I would add is to use disc brake type wheel bearing grease. disc brakes see higher temps.

I believe you will have to un-do all this to replace the ball joints.

85300DT · #7 02-19-2008, 11:18 PM

To make an easier time of getting those hub bolts holding the disc loose is using heat. Hit them with a small mapp gas set up and they are much easier to remove.

JimmyL · #8 02-20-2008, 12:42 AM

Nice thread Rhodes. Thanks!

eagle-co94 · #9 09-01-2008, 09:42 PM

Nice bump for this. Thanks for the info! My passenger side rotor BROKE FREE of the rotor hat and spins on its own! Needless to say my front brakes are shot, so I'm looking to do calipers, rotors and pads all at once.

Oracle12345 · #10 09-01-2008, 09:49 PM

Nice write up for the person has never done it before.

Pretty straight foward and easy even without reading this diy.

Chad300tdt · #11 09-01-2008, 09:50 PM

You can use 1st generation w126 rotors and calipers and you will get vented front rotors with no modifications. Just bolt the parts on.

I used this thread to help me with the job too.

Here's the thread I posted when I did it:
Upgrading w123 with 1st generation w126 brakes

Oracle12345 · #12 09-01-2008, 09:52 PM

Quote:

Originally Posted by Chad300tdt

You can use 1st generation w126 rotors and calipers and you will get vented front rotors with no modifications. Just bolt the parts on.

I used this thread to help me with the job too.

Here's the thread I posted when I did it:
Upgrading w123 with 1st generation w126 brakes

Not really necessary the stock w123 brake calipers and rotors do the job just fine.

Chad300tdt · #13 09-01-2008, 09:53 PM

Not if you get brake fade and haloed rotors.

starrywhite · #14 05-07-2012, 12:18 AM

Thanks for the helpful thread.
Freezing the races really helped, as well as the tip on using the old ones to bang on.
Knocking them in was the scariest part for me. Ears still pleasantly ringing from all the hammering.
Anyway, no more nasty hum in the hub and I'm sure that if those races weren't all the way home, I would have heard some horrible noises immediately.
Felt a bit of warmth at the bit of the hub that protrudes at the wheel after a 6 mile test.
Don't know if that is from the brakes because the disc was hot to the touch. Didn't have time to take the wheel off again to feel the hub itself.
Any advice on what is too hot?

sokoloff · #15 05-07-2012, 02:06 PM

There are specs for the proper amount of grease to add and also specs for end play. Too little or too much can both be problematic. Nice write up.