How to guide to replace front Brake Pads and Rotors on a W123

[79Mercy]

I thought I would make this pictorial for all the people that are clueless as to how to do this job, just as I was at first. I hope this helps everyone.

You need:

2 front rotors
Set of front pads
Disc brake wheel bearing grease
Brake pad paste
10mm hex socket
5mm hex socket
19mm socket
Torque wrench
Channel locks
DOT 4 brake fluid

• Jack up the car and place on good jack stands.

• Use needle nose pliers and pull the old sensors out. 9 times out of 10 they’ll break, don’t worry you have new ones.

• Use a nail or a punch to remove the 2 pins that hold in the bake pads and spring.

• You may have to use pliers to push the pads back and to pull them out.

• Use your 19mm ½” drive ratchet and socket to remove the 2 bolts that hold the caliper to the steering knuckle.

• Hang the caliper by a old wire coat hanger from the torsion bar. Never let it hang by the brake hose.

• Use a flat head and a hammer to remove the dust cap..

• Use a 5mm hex socket to loosen the bolt, don’t remove this bolt, just loosen it.

• Unscrew the bolt from the spindle

• Then the bearing will fall out, looks yummy. Then pull off the rotor.

• This should be what your left with.

• Use 2 or 3 lug nuts and bolt the rotor/hub back to your tire

• Use your 10mm hex socket with ½” drive to remove all 5 bolts, there on there pretty tight.

• Remove the hub and rotor and hub from the tire. The hub should come apart from the rotor, just hit it with a hammer if it doesn’t. Then bolt the hub to the new rotor and put it back on your tire and tighten the bolts to 84 Ft. pounds. Use blue locktight.

• Slide the rotor/hub back on the spindle.

16 slide the bearing back in after you have packed it with grease. Screw the big nut back on and tighten it then back off until you feel it break free(about 1/3 of a turn to the left). You don’t want to much pressure on the bearing or it will not spin freely. Then snug down the 5mm bolt.

• Hit the dust cap back on and then put the caliper back on using lock tight on both bolts and torque them to 84FT pounds.

• Apply brake paste to the back of each pad.

18 push the piston in the calipers back and slide in the new pads.



19 Snap in the new sensors your done.




I hope this will be of help.

[TheDon]

useful

[dmorrison]

Another great post for everyone.

Dave

[Brian Carlton]

I'm a bit disappointed at the omission of the following points:

1) The inner wheel bearing was not removed and cleaned and repacked.

2) The outer wheel bearing was removed, but not cleaned and repacked.

3) The contact surfaces where the pads ride on the calipers were not thoroughly cleaned and greased.

4) The setting of the clearance via the hit or miss method is fraught with risk for a new mechanic who has never done it. If the bearing is tight, it won't last 1000 miles.

[lupin..the..3rd]

Originally Posted by Brian Carlton

4) The setting of the clearance via the hit or miss method is fraught with risk for a new mechanic who has never done it. If the bearing is tight, it won't last 1000 miles.

This rear bearing design is nearly identical to the front bearing design on a Porsche 911.

The method I use for tightening that spindle nut, is to use a large flat-head screwdriver. I insert it in the gap (where the 5mm tightening bolt slides through) and crank it down to where it's about as tight as it will go with one-hand-effort. Then I back it off so it's loose, then I turn the screwdriver until the nut just stops on it's own. "zero torque". Just use two fingers. Then tighten the 5mm tightening bolt.

Also, I wouldn't handle the bearings with dirty gloves. I'd put on a fresh pair for handling the bearings and repacking them.

Also for removing the grease cap, I would not use a flat blade screwdriver. That will damage the grease cap and put it out of round. There is a proper bearing cap puller tool out there, but it's pricey. They method I use, is to grab the bearing cap with a channel lock pliers, then whack the channel locks with a mallet.

Nice pictures though!

[jt20]

Originally Posted by Brian Carlton

I'm a bit disappointed at the omission of the following points:

1) The inner wheel bearing was not removed and cleaned and repacked.

2) The outer wheel bearing was removed, but not cleaned and repacked.

I really hate to drag this up again..

But how do you suggest cleaning and packing the inner bearing without replacing the seal?

How bad could it be to mix two greases which are assumed to be in good condition?

[Brian Carlton]

Originally Posted by jt20

I really hate to drag this up again..

But how do you suggest cleaning and packing the inner bearing without replacing the seal?

How bad could it be to mix two greases which are assumed to be in good condition?

1) You can't.

2) Could be quite bad if the grease(s) is not compatible chemically.

I never take the risk.........all the old is removed.........and all the new is installed.

Do it once. Do it right.

[280EZRider]

The thing about mixing new grease with old is that "High Temp" grease can only be mixed with "High Temp," High friction" with "High friction," etc. The brand is irrelevant.

[tangofox007]

Originally Posted by jt20

But how do you suggest cleaning and packing the inner bearing without replacing the seal?

How bad could it be to mix two greases which are assumed to be in good condition?

How bad would it be if you replaced the seal?

[jt20]

Originally Posted by tangofox007

How bad would it be if you replaced the seal?

devastating.

I just got it out, though I'm quite sure everyone will demand I use a seal press to re-install the new one... that won't be happening.


I also tried the Vstech method of pulling the inner Bearing against the nut.... was not kosher... at least for me.

good info, thanks again.

[79Mercy]

1. true
2. It was re-packed
3. I used the pad paste and cleaned up the pistion before pad insertion.
4. ????, the bearing isn't tight.

[Brian Carlton]

Originally Posted by 79Mercy

1. true
2. It was re-packed
3. I used the pad paste and cleaned up the pistion before pad insertion.
4. ????, the bearing isn't tight.

2. All well and good.........but, the casual observer won't catch it or understand it.

3. The pad paste has nothing to do with cleaning the caliper slides with a stiff wire brush and adding brake pad grease to the slides.

4. For you..........maybe............for others..........it could be.

[TheDon]

Originally Posted by Brian Carlton

4. For you..........maybe............for others..........it could be.

I was instructed when isntalling the bearing retaining clamp/bolt that one should tighten it and back off a hair so the bearing will spin freely

[tangofox007]

Originally Posted by TheDon

I was instructed when isntalling the bearing retaining clamp/bolt that one should tighten it and back off a hair so the bearing will spin freely

Use a dial indicator just once and you will see how absurd that procedure really is.

[Brian Carlton]

Originally Posted by TheDon

I was instructed when isntalling the bearing retaining clamp/bolt that one should tighten it and back off a hair so the bearing will spin freely

The problem with such a description is that nobody can define "spin freely". You back off the nut so that you think that it "spins freely". But, in reality, it needs to back off another 1/16 of a turn to truly release all preload. You don't know this because you didn't back it off the extra 1/16 looking for the point where all preload is released.

The description is fraught with risk and ought to be expanded if one must use the Chevy way of tightening a wheel bearing.

You are aware of the FSM spec of .0005" axial play.........correct?