How to Replace Brake Calipers/ Pads/rear rotor

Reading Time: 8 minutes

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!

How To Remove the Door Panel on W123

Reading Time: 3 minutes

This is an easy job, but unless you know all the hidden screws and plastic tabs you might break the interior, and there are no new interior parts on the market, take care of your door panels.

You need to take off the door panel every time you need to lubricate the window mechanism or clear out the water drains. Or if you need to change the door handle.

Procedure

Locate hidden screw beneath plastic cover in the inside door handle.

door panel w123
Loosen little screw hidden behind the plastic cover

Locate the two screws inside the arm rest.

door panel removal w123
Arm rest screws

Pull put the chrome cover and find the third and last screw for the arm rest.

door panel removal w123
Drag out the chrome cover to locate the upper screw

If you are so lucky so unlucky to have a manual window regulator mechanism. You have to pull off the window regulator handle , drag the plastic cover straight upwards from its center to get it off.

door panel removal w123
Take off the window regulator handle if you have one

Remove the two screws from this door striker chrome cover.

door panel removal w123
Chrome cover

Now comes the tricky part. The front upper corner of the plastic pocket in the door has a plastic clip that sits in the door frame. To get this one off you can not pull outwards on the door! You must first loosen all of the plastic clips around the door edges, and when they all are loose you can pull UPWARDS on the door panel and the clip for the plastic pocket will loose (see image). The only thing that is attached to the car then is the upper edge door panel. Just pull more upwards and it will come off.

door panel removal w123
Pop out the panel from the edges. Then drag up on the panel and make sure the tab is loose located by the

The door has a plastic sheet over the door holes to keep moisture from deteriorating the door panel. Because rain water from the outside window runs down into the door slightly between the seals and leave from holes at the bottom of the door. The plastic cover protects moisture from destroying the door panel. The car is not a u-boat and therefore this plastic sheet needs to be there, if it is old, cut out a new one from some heavy plastic and replace. Just use some random glue to keep it in place while putting the panel back on.

door panel removed w123
Plastic prtection under door panel

As you can see here the edges of the door panel has many white plastic clips, usually some of these old ones break and they are good to have some spare ones at hand.

inner door panel w123
Door panel with plastic clips, replace if broken

 

How to Remove the entire rear Sub frame

Reading Time: 3 minutes

If you like challenges in your life..

Whoa that sounds difficult you could think, I agree it’s not the easiest thing to do in the world. Also doing this without a lift is more tricky, since you have to lower the whole assembly instead of just lifting the car up.

When would you need to do this job?
This is quite a rear job, but changing differential or trailing arms this might be necessary. Also with restoration, body work or mayor overhaul of the car suspension such as replacing those difficult rubber bushings.

Preparation

Set aside time, this is time consuming. Don’t expect to do this on a Friday and be driving again Monday morning unless you are super man. I will rank this maybe even more time consuming than taking out the engine.

Get all the necessary replacement rubber parts, such as sub frame rubber mounts, differential hanger, trailing arms rubber bushings. Rubber seats for the rear springs. New rear springs if needed?

Have at least 3 jacks available. And put your car high up on four big jack stands before starting. The jack stands need to placed in the frame of the car so you can lower the sub frame freely.

No special tools needed other than your large spanners, big sockets and long breaker bars. You will encounter 120Nm bolts here.

Removal Procedure

Step 1:
Remove exhaust system. Check out How to Remove the Exhaust system

Step2:
Remove the propeller drive shaft. Check out How to Remove the Propeller Drive shaft

Step3:
Take off the rear brake Calipers and the sway bar links.

Step4 Lowering the sub frame assembly:

Support the differential with a jack and make sure it can’t slide off. Support also the large sub frame arms with jacks.

jack supporting differential
Jack supporting the differential, note the other two jacks up front supporting the sub frame.
supporting subframe with jacks
Supporting sub frame with jacks, one on each side

Then you have to loosen the two big sub frame tightening bolts. Use a very long breaker bar and lots of force to loosen these bolts.

subframe tightening bolts
Loosen the two big sub frame tightening bolts, then remove the bracket

Then you can take off the sub frame mounting plates by loosening the two bolts to the body.

Next step is to loosen the differential hanger to the differential. If you are replacing this part (you should) then loosen the top four bolts, if not then loosen the two big bolts attached to the differential itself.

differential hanger
Loosen the differential hanger

Now the sub frame is free from the body. Start lowering the whole ting very slowly to release tension on the rear coil springs. Preferably there should be three persons lowering each jack at the same rate, if you are alone you must lower each corner a little bit of a time until the while thing sits on the ground. Use some block of wood to support the assembly while you withdraw the jacks.

Then drag the whole assembly out from the car. Congratulations!

Fitting procedure

Reverse of removal, however don’t forget to place the springs before raising the sub frame. The most difficult part was to align the whole sub frame so the bolts would fit exactly, this is more than a little fiddly.

Cheers, Robs out!

How to Remove the Propeller Drive shaft + Changing center Bearing

Reading Time: 5 minutes

Propeller drive shaft CPR

Removing the propeller drive shaft (also called the center drive shaft) is necessary when you are removing the engine/transmission, changing the flex disks or removing the differential/ rear subframe.

The procedure is similar to most cars and it is exactly the same for W126 and many Mercedes models. So guide this will work for both. Expect some wrestling and sweat underneath the car since the bolts can be very tightly on.

Theory

I highly recommend to change the center bearing, the center bearing carrier and front and rear flex disks when you remove the drive shaft for whatever reason, simply due to the long time of the job it would be a waste unless you also change these wearing parts with limited life span.

Practice
Removal

Step 1:
Remove the exhaust, check out How to Remove the Exhaust system
Step 2:
Remove the parking brake adjuster cables and springs. You will have to unhook the spring from the adjuster in order to get the cables off. The system is basically an adjusting rod with three cables attached to it and a spring to keep tension on the cable whem the parking brake is released.

Parking brake cable tightener
Remove this assembly to get more access to the drive shaft.

Step 3:
Now on to removing the drive shaft!

Loosen the sleeve nut in the middle of the drive shaft, this is to be able to collapse the drive shaft so it becomes shorter when removing it. Have a helper to apply the brakes so the shaft wont rotate when you try to loosen the sleeve nut. I do not like to apply pressure to the Transmission with the gear in Park due to the possible damage this may cause. Have the car in neutral instead.

sleeve nut drive shaft w123
The Sleeve nut, needs a very large spanner”

Next step is to remove the flex disks, there are one at each side of the drive shaft. The bolts are of a self locking type (the nuts are not completely circular) and they are hard to remove since they are not meant to get loose when you drive. I actually broke my spanner trying to get one stuck bolt off, so here I recommend some long spanners or some form of extension on the spanners to get more torque. Remember simple physics where the torque = force x length, so the longer the better when loosening stuck bolts and nuts. To get the drive shaft off you only have to remove three nuts. The ones that are attached to the drive shaft spider. If you are planning on replacing the flex disk, then you have to remove all 6.

There might be tricky to access a spanner on the side facing the transmission, and you might end up supporting the transmission with a jack and removing the rear transmission mount.

front drive shaft flex disk w123
Front flex disk

Unfortunately you have to remove the three nuts at the differential end as well,  the access here is easier though.

rear flex disk w123
Rear flex disk

Now the drive shaft is hold in place by the center bearing carrier. The center carrier is just hold there by two bolts in the chassis.

drive shaft center bearing carrier
Center bearing carrier

Now you have to collapse the driveshaft by pushing the front side of the shaft in towards the middle to get it loose from the transmission spindle.

The drive shaft can be so corroded onto the flex disk mouting plates that you will not be able to do this easy by hand. I used a long screwdriver to place it between the drive shaft spider and the flex disk and used massive force until it broke loose.

Warning: You might end up damaging the flex disk which i did. It was so corroded that one tab of the flex disk broke off wæstill attached to the spider.

Caution: Be careful when handling the drive shaft so it doesn’t come slamming into the ground or on youself for that matter. The drive shaft needs to be perfectly straight and it is also balanced by the factory to a, so be careful eh?

drive shaft w123
Drive shaft separated
Bearing Replacement

The bearing is most likely stuck in the drive shaft center carrier, always replace this cheap rubber part or your drive shaft will vibrate while driving. Just rip it off or use a knife to cut it so you can access the bearing.

The Bearing is pressed is pressed on the shaft and you need a puller tool like this. Note the placement of the dust caps around the bearing, so you place the the same direction when fitting the new bearing.

puller tool
Bearing puller tool

After pulling out the bearing, insert the new bearing into the new center carrier.

bearing parts w123
Parts distributed, bearing dust caps, center sleeve, new center carrier and bearing, old one to the right.

Remember to insert the inner dust cap before tapping on the  new bearing.

inner bearing dust cap w123
Inner beaing dust cap placement

Use a metal tube to tap on the inner part of the bearing, be careful with the hammering and do this slowly.

tapping on new center bearing driveshaft
Tapping on new center bearing on the drive shaft with a tube
Assembly

Assembly is pretty much the reverse as removal, however you need to spin the drive shaft around a few times after fitting, before tightening the sleeve nut, this is to remove stress on the drive shaft before tightening. The last thing you should do is tightening the sleeve nut!

Always follow the torque specifications on the flex disk bolts!

Cheers, Robs out