How to Replace the Front Brake Rotor and Front Wheel Bearing on W123

Changing the  front rotors on W123s are much more involving than changing the rear ones. The front rotors are bolted onto the hub from the inside and the whole hub with bearings and everything have to come off. The job is not difficult but needs some preparations with tools and grease.

The rotors should be changed every time there are large scoring, a big edge lip, excessive rust or they have been overheated and warped. The good thing about this job is that you can change the front hub bearings (which is of an open type) at the same time! The bearings should be re-greased at set intervals and changed when there is play in the hub.

Ideally you would need a dial indicator tool, which is just a dial fitted on the hub while you are pushing and pulling on the rotor that tells you the end play. I would recommend this if you are planning to do bearing inspection and replacement often. For the front bearings it is not really that crucial. It is much more crucial on the rear bearings which are closed types with much less tolerance in the bearing play, these rear ones cannot be easily adjusted when setting the final end play.

Fore time reference I used around 6 hours to change all four brake rotors on the car, where it took more than 4 just for the more involving front ones. Cleaning off old bearing grease and loosening rusted bolts takes up most of the time.

Preparation

Get the necessary parts:

  • New front rotors
  • New front brake pads
  • (New brake pad sensors x4)
  • New front bearings if needed, although recommended
  • Wheel bearing grease
  • Thread locker

Check that you have the right tools:

  • Pipe tools and with hex bits for removing the rotor from the hub.
  • Long breaker bar
  • Hammers, both carpenter hammer and rubber
  • Chisel and punch tool
  • Brake caliper piston separator tool
  • (Dial indicator) recommended, but possible without
  • Torque wrench
  • Pliers
  • Brake Cleaner
  • Lots of shop towels
  • Plastic gloves
Removal Procedure

Start by jacking the car up and put on jack stands. Its fine with only jacking the front up, your choice, but remember to engage parking brake and use wheel stoppers to prevent the rear to start rolling.

wheels w123
Remove the front wheels

Remove your fine rims and wheels. Now is also a good time to clean them really good on the inside! Ohhyeah..

Now the wheels are off you have to start cleaning brake dust before you start doing anything else. Use a dust mask, grab a brush and lots of soapy water and start cleaning the caliper, the disk and hub and around the immidiate area. This is to bind the dust to the water so you will not inhale it later.

Start by removing the brake pads, throw these away. Then go ahead and unbolt the two caliper bolts, hang the caliper in some zip ties or string up in the wheel well for easing tension off the flexible brake hose. The front calipers are quite heavy so prepare the zip ties or string before you loosen the last bolt.

Now is the time for removing the front wheel hub. The exciting part.

w123 hub cap
Hub cap

That black metal cap on the tip of the wheel hub is the hub grease cap. It needs to be removed. It is just pressed on the tip and, you can remove it by using a hammer and a chisel, just knock carefully on the little edge outwards, repeat by turning the hit point, then the cap would move outwards until it pops off.

Once the grease cap is off. you can see inside and there is a spring which is the ground conductor for the brake pad sensors and the hub tightening screw. I have seen these springs broken since they are quite fragile, and they have to be intact for the brake pad sensors to work. Remove it by pulling it straight out with some thin pliers. Then loosen the hexagon screw on the wheel hub locking nut. Be sure to count the number of turns it takes to take it off then write it down. This number is the reference for the wheel hub play, when you don’t have a dial indicator it is very nice to know, although it might need to be adjusted when reapplied new grease and new bearings.

hub locking nut w123
Hub locking nut. Don’t forget to count the number of turns.

When the hub bearing lock nut is loose, you can take off the outer bearing and also grab the brake rotor, just pull the whole hub assembly off.

the hub spindle w123
The hub spindle
outer bearing w123
The outer bearing

Now it is time for cleaning, the most time consuming part of the whole thing. Clean the old grease off the hub. Also clean the old grease off the outer bearing if you plan to reuse it and look for wear. If any scoring is evident on the bearings, just replace them. Use lots of brake cleaner and let it soak before going crazy with shop towels.

inside of front rotor
Locate bolts inside the rotor

Place the old brake rotor in a wise and tighten it really hard, I mean so hard you are able too. Use the large breaker bar with the hexagon pipe and crank off all the five bolts holding the brake rotor and the outer hub together. They usually have rusted tight to the rotor and they also have thread locker.

unbolting front rotor
Place old rotor in the wise and loosen the really hard bolts.

Even after the bolts are off the rotor and hub might be fused together. You may need to bang the hub free with a hammer to fully loosen it from the rusted brake rotor. Then clean the hub free from the old grease and reapply with new bearing grease if you’re not planning to change bearings.

front hub free
Hub free off the old rotor

If you are changing the bearings, the inner bearing have to be knocked out of the hub by using a socket which will just fit inside the hub. Ideally you should use a brass punch tool, but since most of us don’t have this exotic equipment then go for the socket. The socket will ensure evenly force distributed over the bearing race.

new vs old brake rotor
Good time to change the brake rotor
Fitting Procedure

Making sure that everything is very clean, of the hub and inner hub.

The inner hub bearing can be driven in by using a same sized socket as the bearing itself, make sure you hit it so it will go in perfectly straight, this might be a bit tricky at first, but when its a bit in the rest should be easy. Do not hammer directly on the race of the bearing since it will be broken.

greased hub w123
Hub all greased up

Start by reapplying bearing grease. Fill around 2/3 of the round hub with new bearing grease otherwise it might be tricky to get it on the spindle. Also apply some brake pad grease between the surfaces of the hub and the rotor to prevent seizing. Use some thread locker on the rotor bolts and tighten the bolts to 114Nm with a torque wrench. Be sure to not put the new brake rotor in a wise without some protection of the rotor surfaces.

fitting new rotor to hub
Fitting the new rotor to the hub

THIS PART IS VERY IMPORTANT!

The brake rotors are coated in some anti rust protective layer that will make your brakes pretty much useless unless you clean the rotor surfaces with brake cleaner before you fit them on the car. Be sure you remember this before you put them on the car, and clean them properly, you can feel the stickiness goes away and it feels more like bare metal.

Slide the outer hub and rotor back on the spindle, place the outer bearing in too before tightening down the wheel hub with the tightening nut. Turn it as many turns as you counted before, then check the looseness with wobbling the brake rotor back and forth. If any looseness is apparent then tighten the nut slightly so no apparent looseness can be felt.It is important to not over tightening the hub since it will overheat. Ideally you should use a dial to get the exact manufacturer setting.

Secure the tightening nut and place the little ground spring in place.

Fill the grease cap with some bearing grease and tap it in place carefully with a rubber hammer.

Don’t forget to put on the brake calipers on and placing some thread locker on the bolts before you tight them down to about 110-114Nm. At last before the wheel goes in put in the new brake pads and replace rattle springs or pad sensors if needed.

front rotor w123
New front rotor!

Then put the wheel back on and repeat the whole progress again on the other front wheel. Hopefully it takes less time than the first one.

Cheers!

How to Replace Brake Calipers/ Pads/rear rotor

The brake fluid is hygroscopic, which means it will absorb water moisture over time. This is the primary reason for changing brake fluid regularly, at least once every two years. When the brake fluid contains water it will make the internals of your brake calipers start rusting and the pistons will begin to stick, leading to overheated wheels that can; worst case cause fire due to overheating the rotor and/or make your wheels drag like you are slightly braking all the time.

So if you have sticking brake pistons and they are beyond repair, then a caliper change is necessary. Thankfully the calipers for the w123 are not that expensive, where the rear ones are quite cheaper than the front ones. I will go over how you change the caliper for the rear, but the procedure is nearly exactly as the same the front. If you have never worked on your brakes, then I recommend having someone around that is familiar with brake change or you read upon the topic very seriously and prepare thereafter. This job is one of those highly critical areas where you have to make sure you do it right before you start driving! That aside, working with brakes are in fact quite simple and when you have done it a couple of times it will be no stress at all.

You should consider brake maintenance your primary safety concern:

  • Change brake pads before they are worn out
  • Do regular brake fluid changes
  • Inspect wear on the rotors, check for excessive “lip”
  • Inspect flexible brake hoses for wear
  • Inspect brake hard lines for corrosion
  • Feel that the brake booster is working

If you are changing the calipers, they have to be done in pairs i.e. on both sides of the car. The same applies for the brake pads.

Take care of your health, you should wear a dust mask to prevent breathing in brake dust particles. Also to avoid the dust altogether, after taking the wheel off -> Use soapy water and a big brush to clean down the caliper and around the rotor and brake shield. This will prevent dust from floating around in the air while working.

Preparation
  • Brake bleeding kit or a companion to work the pedal
  • Clear tube
  • Caliper if you are changing them
  • Brake pads, they are stupid cheap and not to change them when working on the brakes are dumb
  • New brake sensors for the front pads
  • New flexible brake hoses if they are more than 10 years old
  • Locktite thread glue
  • Consider changing the rotors if they have a large lip
  • Brake pad grease, i.e. Lubro Moly LM508
  • Brake fluid
  • Necessary tools and torque wrench
Procedure Removal

Apply braking pedal, put a stick or something so it is depressed throughout the job, this will prevent some braking fluid loss. Jack up the necessary wheels and put your car on jack stands. Take off the wheel and clean the caliper area with soapy water.

rear caliper
Old caliper, looks ok from the outside, but in fact completely useless and sticking pistons. Also completely lacks pad rattle spring, probably rusted a long time ago.

The brake calipers can be of different types primarily of ATE or Bendix, they are quite similar though and if you bought a pair of new ones without knowing the type you had it does not really matter when you are throwing out the old ones anyway. They use the same fitting bolts, brake hose inlet and brake pads. The major difference is the construction of the brake pad locking system and using different internal seals.

caliper front
Front caliper with brake pad sensor. Note the right sensor is missing

If working on the front, start by removing the two brake pad sensors. The brake pads are secured with two locking pins and a spring is holding the pads down to prevent rattling. The two locking pins are either hold in by a clamping spring so you have to use a long and thin driver to punch it in, or they can be held in place by a security pin on the end. I mostly encountered the ones you have to use the long driver and a hammer to get out.

old and new brake pads compared
A good reason to change the brake pads, completely worn beyond the pad sensor, which didn’t quite give a pre warning. Brakes went through Norwegian mountains and started scraping on the old rotor. Good thing to have manual gear and drive home without using the brakes like a pro.

When the pins are removed, use a screwdriver or maybe you have brake pad remover tool to pull the pads out. If you can’t get the pads out because they are stuck due to rust, then you have to get on disconnecting the caliper and use a hammer to knock off the entire caliper. This is frustrating when you are only changing the pads. (Happened to me once, look under)

front caliper stuck, remving with a hammer
Removing stuck pads by unbolting the caliper and hammering the entire caliper off

If you are only taking off the calipers to do this or changing the rotors and not the calipers, then you can go on undoing the caliper bolts without taking off the brake hose, in that way you don’t have to bleed the brake system. Taking off the calipers are necessary if you are for example changing the struts, the rear drive shafts or something that require you to have the trailing arm fully suspended which will put excess pressure on the brake hose. Don’t leave the caliper hanging from the brake hose since it can damage it! Tie it up to something under the car with some zip ties.

If you are changing the brake calipers, then start by taking off the brake hose. If you are changing the brake hose or not, start by using a hose clamping tool (which are made for this purpose and not pliers or similar!) on the brake hose to prevent brake fluid spillage and emptying the fluid reservoir. Also if you are dealing with the front calipers, then remove the brake pad sensor wiring harness from the caliper.

clamping the brake hose with clamper
Preventing fluid spill with a hose clamping tool, Don’t use other sharp tools if you are planning on using the hose later.

Now you can start undoing the caliper bolts, there are two of them and they are on quite tight.

By now you have successfully removed the caliper, not so difficult eh? The choice is yours to change the brake rotors, my guess is that if you are replacing the calipers, the rotors are probably worn a lot too. The front brake rotors needs quite a procedure to be replaced (I will cover that in another how to..). The rear ones are easy to pull off. Disengage the parking brake. Sometimes you can just pull out the rear rotors by force, but often they stick to the parking brake shoes. They can be adjusted to be less tight by turning a star screw through one of the wheel hub bolt holes. It should be 45° from the diagonal towards the front of the car, use a torch to peek in. Once located, use a thin flat headed screw driver to turn the screw until it gets loose. I can’t recall if it’s up or down, you will figure it out quite fast. This means that you have to tighten it once you put on the rotor again or your parking brake is not going to be working.

Now you can go on removing the brake hose, here you have to be careful since the brake line can break or you can damage the fitting if the brake hose is stuck or completely rusted. Try to loosen it, but if it will not come loose without the use of excessive force, leave it and put the other new parts on. Better to at least have a car you can drive than a broken brake hard line, instead take the car to a workshop later that can replace your hose and possibly change your old brake lines as well.

Be fast since brake fluid is going to come out when you remove the hose and clamp.

old and new rear caliper compared
Comparing old caliper with new one, also new brake hose.
Refitting

Put that brake hose on fast and tighten, then put on the hose clamper on again. Now check your brake fluid reservoir and refill until slightly under maximum mark. Leave the cap off.

Put on your rotor again and adjust the parking brake with the star nut. Check the tightness by turning the wheel, it should have a light drag to it.

When putting back the caliper again, the bolts need to have a little bit of thread locker applied to the threads since there are no washers or other methods to secure the bolts from coming loose. Remove old crud on the threads before. Liining up the caliper while finding the threads can be a bit tricky, especially while trying to do it before the thread locker dries, so apply thread locker to only one bolt at a time. Use your hand to put the bolt in by hand top ensure you don’t cross thread. Do the final tightening with a torque wrench, since over tightening might lead to the bolt head snapping off and then you have no brake calipers going down the road…

new rear caliper
New rear caliper, yeeeiii!

Put on the the brake hose, don’t over tighten. Now you might have to push in the pistons, this can either be done with a brake piston tool or using the end of a crowbar leaning against the rotor to push it in. This is why the fluid level cap should be off and the reservoir not completely full, since there might be fluid that can squirt all over when you push the pistons in. Check the level and extract some fluid if it’s getting over maximum.

Put a little pad grease on the sides of the pads where it sits in the caliper housing then put them in. Fit the pad spring and retaining pins. Make sure the bleed nipple is tighten. Now the calipers are ready to be bled from air.

Brake bleeding

Fill up the reservoir to maximum. When you have been doing caliper changes on only two wheels, then you don’t necessarily have to bleed the whole system since there are two circuits. You should start by bleeding the caliper furthest from the reservoir and work your way towards the closest to the reservoir. It is very important that the reservoir do not get empty while doing the bleeding, which means air has gotten into the system from the top and you have to do a full system bleeding on all calipers. Always check the reservoir often and refill after every bleed of one caliper!

Bleeding kit:

If you have a brake bleeding kit, then put the tube over the nipple and start pumping until you get vacuum, open the bleed nipple slightly until you see only clear fluid without bubbles coming out then shut the nipple again. Refill the reservoir until max. Repeat with same procedure on the next wheel you have been disconnecting the caliper.

Without bleeding kit, but with helper:

You at the caliper with the bleed nipple is the dictator, the helper at the brake pedal is the slave which must not do anything without permission and your commands, otherwise you have to start the bleeding over. You need a clear tube running in to a bottle with fluid where the lower end of the tube is submerged in fluid. You should be able to see clearly the state of the fluid coming out of the tube. The clear tube needs a tight fit over the nipple so no air can come in and give you false readings.

You start out with the nipple shut and the brake pedal disengaged. You open the nipple and you give the helper permission to depress the brake pedal fully, break fluid will come out, you then shut the nipple again while the brake pedal is depressed. After the brake nipple is tight, you give the helper to release the brake pedal. Now you repeat the process slowly and controlled, and you clearly check if the fluid coming out is with or without air bubbles. You also have to make sure the reservoir is not becoming empty. When no air bubbles can be seen coming with the fluid, the caliper is bled and you can move on to the next wheel.

Checking brakes after bleeding:

When done make sure the reservoir is on the maximum mark. Put on the cap again and feel your brakes. The brake pedal should be completely stiff after a few pumps and not get soft when you hold it down under force. Start by doing some braking while going slowly at the parking lot. Then test once at higher pace. If your brake pedal feels completely stiff and your car stops immediately after hard braking, then job well done! If your brake feels squishy then you have to restart the bleeding procedure.

Cheers!