Mercedes CLS55 E55 AMG 55K Front Brake Disc and Pad Change


A brief guide on changing the front brake discs/rotors and brake pads on the Brembo AMG 55K braking system with 8 piston calipers.

What You Need:

  • Hammer
  • Copper Grease

DISABLE SBC!!!

Most of these cars have the Senstronic Brake Control (SBC) fitted and provides electronic braking assist and control which applies pressure to the entire braking system when various conditions are met even including doors opening. The pressure is huge and can quite easily crush fingers or other objects so it must be disabled or disconnected when working on the braking system.

This can be done using STAR or by disconnecting the SBC unit under the bonnet/hood. I used the option in the STAR diagnostics menu.

1. Loosen the Wheel:

The 5 bolts are 17mm, 1 of them will be the locking wheel nut. Start by using the breaker bar and 17mm socket together with the locking nut to break the bolts free – don’t remove them just yet.

2. Jack the Car

Use the jack point under the sill to position the car and jack it up until the wheel is off the ground. Now remove the bolts from the wheel and lift it off the rotor. The brake disk and caliper will be bare now. I placed an axle stand under the solid (non-plastic covered) part of the axle point and removed the jack.

3. Parts Of Interest

highlighted

Red: Disk Retaining Bolt (T30)
Yellow: Hub/Disk Joint
Green: Pad Spring Retaining Pins
Blue Arrows: Main Caliper Mounting Bolts – behind the caliper, perpendicular to the disc
Purple: Secondary Caliper Mounting Bolts
Orange: Pad Wear Sensor Mounting Bolt – facing perpendicular, inwards (if fitted).

4. Remove the Pad Retaining Springs

Using a suitable retaining pin removal tool or a narrow screwdriver, hammer out the retaining pins being careful not to let the springs pop out when the pressure is released.

20150606_123542

You can see the two pins removed for the two sets of pads and the springs have been set aside.

5. Remove the Pad Wear Sensor (If Applicable)

Not all cars have this (and if installed, not all hubs have one). If present, there is a bolt on the inner side of the caliper facing inwards (marked ORANGE) in the picture above. Use the E10 Inverted Torx socket to undo this bolt and disconnect the wear sensor. Note that this bolt is threadlocked.

If you are just changing the pads, it may be possible to slide/push them out of the caliper now if they aren’t too well bed in with dust/dirt/rust. The new ones can slide in and the springs refitted – that’s it – if you’re lucky! If they don’t come out easily, you’ll need to remove the caliper from it’s mount.

5. Removing the Caliper

If you are just changing the brake pads, remove the Secondary Caliper bolts (marked in PURPLE) which face towards the rear of the car. This requires the 10mm Hex Bit. The bolts sometimes come out all the way with their washer but may separate the caliper and remain in situ. Don’t force them out as the thread has a tendency to catch on the washer if undone too far.

If you are changing the discs (rotors) as well, it is better to remove the main caliper mounting bolts in case the discs are fused to the hub as this provides a method of removal. These are on the inner side of the disc and require the 21mm socket to remove.

In both cases, these bolts are VERY tight and thread locked so need a pretty reasonable amount of force to remove.

The caliper will now be free and can be slid off the disc. Make sure you have something to rest the caliper on and avoid stretching the brake line. I used a sturdy cardboard box that was the right height.

6. Remove the Disc (Rotor) Retaining Screw

Marked in RED in the image above, use the Male Torx T30 bit to loosen the retaining screw. Don’t remove it fully yet as it acts as stops the disc falling off (either as soon as the caliper is removed or later on if it is rusted on).

This bolt has some threadlock applied so will be a little difficult to break and you may need to secure the disc to stop it moving when you undo it.

7. Replace the Brake Pads

Using some brake cleaner, and whatever force necessary, pry the old brake pads out of the caliper being careful not to damage any of the 8 pistons (2 per pad). Give the caliper a clean out and slot in the new pads. This may take some angling and manoeuvring to get them in place. They can only fit in one way and it is obvious by their shape. Use a thin spread of copper grease on the rear of the pads to help eliminate squealing.

Use a caliper compressing tool or similar (I used a C-Clamp) to push the pistons in. These operate in pairs to I made use of the flat brake pad surface to compress them together. The gap in the caliper must be sufficient to allow the brake disc to slot in-between. If the brake fluid has been topped up, you may beed to bleed or drain some out from the master cylinder – I didn’t have to do this.

8. Remove the Brake Disc (Rotor)

This has the potential to be the most awkward bit. If you’re very lucky, the disc will come loose with a couple of tugs and you can remove the retaining screw fully.

However, chances are that over time, the discs have heated and cooled and succumbed to rust and as a result, fused quite strongly to the hub. I tried soaking the holes and joint (marked YELLOW) in the picture above and the rear of the joint with rust penetrant and giving it a couple of hits with a hammer around the edges but it would not budge. I was reluctant to apply more force to the hub for risk of causing damage to the wheel bearing so I used the ‘Two Bolt, Two Nut, Two Washer’ method. See here.

20150607_131429

9. Fit New Brake Disc (Rotor)

Now that the disc is off, clean up the hub surface to ensure it is free from rust and other dirt and coat the surface liberally with copper grease to help prevent any seizing for next time.

20150607_135446

 

The new disc lifts and slides over the hub and bearing and rests flush against the surface with the bolt holes. Align the retaining screw hole with that of the disc and use a new screw to secure the disc to the hub (Torx T30).

20150607_140930

 

10. Re-attach the Caliper

Slide the caliper onto the brake disc (hopefully the disc will fit between the pads because the pistons have been compressed back).

Depending on which bolts were removed, reattach the caliper to the hub mounts. Use copper grease and threadlock on all the bolts and if you have a torque wrench make sure they are done up to spec. Remember, they are very tight!

20150607_153235

Nice and Shiny :)

Reattach a new pad wear sensor at this point and rebolt it to the caliper using the E10 bolt.

Also refit the pad retaining springs and pins at this point.

11. Refit the Wheel

In the reverse of the earlier process, the car may be lifted on the jack and axle stand removed. The wheel can be reattached using the 17mm bolts and locking nut and then lowered back down. Tighten by hand initially to prevent cross threading and then use the breaker bar to lock them in.

12. Bed in the New Brakes!

Refer to the manufacturer’s instructions but I usually do around 5-6 gradual stops from around 40mph letting them cool in between and then a couple of faster, harder stops, again letting them cool in-between.


3 comments

Leave a Reply

%d bloggers like this: