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

rhodes2010 · #1 02-19-2008, 02:31 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.