W211 rear brake change

[ChrisEdu]

There are 5 holes to access the adjuster

I can't see it through them! All I see are springs.

 

[ChrisEdu]

Take the retaining screw out, remove the disc and see if you can see the adjuster mechanism with the disc removed? It should look like a little cog. Maybe it's had new, but incorrect discs fitted without the hole?

I took the retaining screw out of the disc, but it ain't budging, presumably because the parking brake is still on?

 

[ChrisEdu]

I'm thinking that the 'easiest' option is going to be:
a) chock the front wheels
b) get trolley jack onto the rear diff and jack the entire rear end of the car
c) put axle stands under the rear side jack points
d) take off the parking brake
e) either celebrate, as the discs can now rotate freely and I can remove them, or scream in horror as everything comes crashing down!
f) assuming the best case scenario from step e), continue to replace the disc, pads, and reassemble, remembering to put some copper grease on hub, back off pads, etc..
g) remove the axle stands from the sides
h) lower the car back to the ground, and reapply the parking brake
i) remove the chocks
j) celebrate a job well done!

Does this sound correct, or have I missed anything?

 

[pmcgsmurf]

I presume those photos show what you get after removing the brake disc?

Yes.

 

[pmcgsmurf]

I took the retaining screw out of the disc, but it ain't budging, presumably because the parking brake is still on?

You mean the Parking (hand / foot) brake? You need the parking brake off.

 

[OneForTheRoad]

I can't see it through them! All I see are springs.

Put a wheel bolt partially in, otherwise the disc will turn on the hub behind it and you'll lose the holes to look through. Its best done at night with a torch tbh . Shone into a hole turn the disc and hub slowly until you see the cog.

 

[MrGreedy]

Put a wheel bolt partially in, otherwise the disc will turn on the hub behind it and you'll lose the holes to look through. Its best done at night with a torch tbh . Shone into a hole turn the disc and hub slowly until you see the cog.

This! Although if you have a disc retaining grub screw holding the disc on firm to the hub face, you shouldn't need the wheel bolt. You only need the wheel bolt if the disc brake is 'spinning' on the hub face and causing mis-alignment with the wheel bolt holes in the hub face.

I think the torch advice is good too. Difficult to see in there, especially on a nice bright day outside.

You need the parking brake/handbrake/electronic handbrake disengaged; be that operated by a foot brake high up on the left of the drivers foot well, a hand brake lever or electronic parking brake.

You will not be able to remove the rear disc with the parking/hand brake on, because it acts in the same way as drum brakes pressing on to the inside of the inner boss of the brake disc, gripping it tight.

You might still not be able to remove the disc even with the parking brake released, as there might be a tiny lip on the inside of the boss caused by natural brake disc wear over time, and therefore the adjuster might need to be slackened off further to allow the lip on the inside of the disc to clear the rear brake shoes.

 

[ChrisEdu]

This! Although if you have a disc retaining grub screw holding the disc on firm to the hub face, you shouldn't need the wheel bolt. You only need the wheel bolt if the disc brake is 'spinning' on the hub face and causing mis-alignment with the wheel bolt holes in the hub face.

I think the torch advice is good too. Difficult to see in there, especially on a nice bright day outside.

You need the parking brake/handbrake/electronic handbrake disengaged; be that operated by a foot brake high up on the left of the drivers foot well, a hand brake lever or electronic parking brake.

You will not be able to remove the rear disc with the parking/hand brake on, because it acts in the same way as drum brakes pressing on to the inside of the inner boss of the brake disc, gripping it tight.

You might still not be able to remove the disc even with the parking brake released, as there might be a tiny lip on the inside of the boss caused by natural brake disc wear over time, and therefore the adjuster might need to be slackened off further to allow the lip on the inside of the disc to clear the rear brake shoes.

Does this mean that the adjustment screw still needs using to remove the disc, even if the park brake is off?

 

[MrGreedy]

Does this mean that the adjustment screw still needs using to remove the disc, even if the park brake is off?

Potentially, yes, depending on how the brake is currently adjusted and/or the amount of wear on the inside of the boss (if it created a lip)

 

[pmcgsmurf]

Does this mean that the adjustment screw still needs using to remove the disc, even if the park brake is off?

Very unlikley you will get the disc off without backing the shoes off.

Unlikely but either way you still have to find the adjuster to adjust the shoes so best do it now.

Can be very tricky to locate if you haven't done them before.

 

[OneForTheRoad]

You'll have to adjust the shoes again once the new discs go on. Then the fun begins Mark the location of the star wheel on the new disc with a marker pen, so you know where it is for next time.

 

[ChrisEdu]

You'll have to adjust the shoes again once the new discs go on. Then the fun begins Mark the location of the star wheel on the new disc with a marker pen, so you know where it is for next time.

Who says there'll be a next time!

 

[ChrisEdu]

Some success today. Managed to get the car up in the air and supported, so the parking brake could be released. Managed to get the left side disc and pad replacement done, albeit after a fight with the old disc to get it off, even after winding the parking brake all the way off. So, one down, one to go, my nemesis from yesterrday!

Managed to find the adjuster for the parking brake and wind it fully off. Again, the disc didn't want to come off, so needed a fair bit of persuasion with a club hammer! So, with that off, I fitted the new disc, all well and good.

Next task, pop the brake pads in and re-fit the caliper assembly.

Inner one, with the sensor went in fine. Outer one though....... different story altogether! It would not fit! I checked with the one that came out, again, no joy, it won't go back in!

So, it looks as though when the car fell off the jack the other day, the caliper bracket got just slightly bent out of shape, not a massive amount, maybe a couple of mm at most, but enough to stop the pads sitting back in the guide channels. Therefore, it looks like I now need to buy a new caliper bracket! Yet more delays. So close, but so far from finishing!

 

[ChrisEdu]

Found a company that specialises in breaking Mercs, so have been able to order a replacement caliper mount, and caliper, for less than half the cost of a new mount.
It should arrive in a few days, so then hopefully, I can finish the job.

 

[Carabind]

Did you use axle stands or just reply on the jack? (if the latter, not a criticism, we’ve all done it , but it’s an potential important learning curve for other readers )

 

[ChrisEdu]

Did you use axle stands or just reply on the jack? (if the latter, not a criticism, we’ve all done it , but it’s an potential important learning curve for other readers )

Second time round, ie today, I jacked the rear end, using my trolley jack on diff, and put axle stands under the side jack points, also having put chocks front and back of front wheels.
First time, thanks to migraine scrambling brain, just had one rear jacked on Merc jack at side point. Opps! Lessons learnt!

 

[OneForTheRoad]

Big no no using the diff it can crack very easily.

 

[ChrisEdu]

Big no no using the diff it can crack very easily.

Seems to be an area of contention, with some saying it's fine and others the opposite. If not, where else can you jack the whole back end?

 

[pmcgsmurf]

First time, thanks to migraine scrambling brain, just had one rear jacked on Merc jack at side point. Opps! Lessons learnt!

I asked earlier, couldn't understand how letting the Parking Brake off would cause it to move if it was on stands, now i get it.

Always crack the wheel bolts, chock the front wheels jack up and put it on axle stands.
If going underneath a few extra stands etc. are what I'd always use along with the wheels under the sills and some very large short wooden sleepers.

 

[whitenemesis]

Big no no using the diff it can crack very easily.

Pretty sure MB recommend this, as do many other sources for raising the rear to place on stands.
I can imagine the cast casing could crack if subjected to a sharp blow but just supporting the car's weight for a relatively short duration?