124 front brake discs and pad change

The Crooner

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Hello

Have just bought genuine MB discs and pads for the front of my 124. Having just read jibcl500's comments on the "which brake disc thread", was looking for advice/work instruction so that we can do more than just unbolt/bolt back on.

Have also purchased new calliper bolts, disc retaining bolts and pad wear sensors.

So, kind people, how do we do it properly?

Thanks

Tony
 

television

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Then its very straight forward, just unbolt them and fit the new parts ,do have something high enough to rest the caliper on, as it must not be left hanging on the flexible hose.

If necessary, file or sand off the paint on the edges on the new pads so that they are free to move in the slots easily, and this will prevent them from sticking.

I think that I would clamp the pipes to retract the pistons, and undo the bleed nipple (if they will undo, any risk of them breaking then just push the pistons back making sure that the header tank does not over flow ) this wouls avoid pushing any rubbish into the expensive ABS pump
 
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The Crooner

The Crooner

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OK thanks, that is hat I thought.

I had read this:

Replacing disks and pads isnt as straight forward as just remove and replace, all crud and crust needs to be removed from the calipers, any surface of the caliper that has contact with the pads edge needs to be smooth and clean, all pins and spring plates either replaced or cleaned.

Hubs where the disk bolts too needs all rust removed so the surface is smooth and flat. Brake grease needs to be used in several places as specified by MB.

I can change front disks and pads (both fronts) in under an hour but to do it properly takes easily an hour per corner.

The result is better longer lasting brakes. Took two hours to recondition one caliper on my CL today.


and wondered what the reference to grease was.

I now suspect that the cl has a different set up.

Thanks again

Tony
 

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Removing rust ? just a light sand of mating surfaces is fine, and only minimal sanding or cleaning is required.

Re the greasing, there are several schools of though on this, and this is referring to the grease that is used to stop squealing. MB say that only the face of the piston needs to be greased, others say the rear of the pad and shim.

This is of coarse the copper grease, made for brakes.

Any other crud or what ever its called is a cosmetic thing and plays no part in the operation of the caliper, where sliding shoes are concerned, these parts should be clean and rust free where possible
 

roadhog

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I'd be surprised if the CL had a much different setup from other cars. The grease referred to is (as per TV's reply) the copper grease used on the back of the pads/face of the pistons.
I tend to lightly cover the rear face of the pad and the sides, make sure you don't get any on the friction material. Give the new discs a good clean before fitting to remove the rust inhibitor they're usually covered in. Brake cleaner and a bit of scotch brite work well for that.

Something like a Haynes manual is a good starting point. In general, you should aim to replace the pins and springs that hold the pads in. Make sure all mating surfaces are scrupulously clean. I use a steel wire brush for the hub mating face and a small brass wire one for the insides of the calipers. Do take care around the piston seals. If you have sliding pistons, pull out the sliding pins and clean/grease them before refitting.

It's really not difficult but if you're at all unsure then pay someone to do it.
 
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The Crooner

The Crooner

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Thanks for that, I'm not unsure, just want to be certain that the Merc does not require anythiong other than what I've always done.

This discs are MB and have grey paint on them, I guess I need to clean it off the friction surfaces.

Tony
 

wireman

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You must ensure the face of the hub flange is clean and flat, this is one sanding/emery job that must be done.
This ensures the disk runs true, mount the disk and check for axial run out with a DTI, while the DTI is in place check the wheel bearings for end float (.01mm-0.02mm/ 0.4-0.8 thou) and if excessive adjust it before you check the disk run out.
Use the wheel bolts to secure the disk for checking, the one that holds the disk in place will not be sufficient to keep the disk flat, don't over tighten this bolt it only stops the disk falling off/moving during servicing (hence muck getting between the disk and hub) and can be a job stopper if its head gets damaged whilst attempting to remove it.

Also the "guides" (where the pads are supported) in the caliper body atop and below the pads backing plate must be clear of rust and debris, another emery job. Clean the caliper up not the new pads if they are a tight fit.

There are several types of brake squeal compound formulated for application on the back of the pad/piston and nowhere else, this helps prevent squeal, my choice would be the stuff from MB here, use coppaslip if you must but it a'int the same.
A little dab of coppaslip helps keep rust at bay on the pad guides and face of the hub flange, only a little smear not a blob.

Whilst your caliper and disk is off check the ABS reluctor ring (on the inboard end of the hub) for rusting away and clean the sensor of the bits of magnetic stuff that stick to them and mess up the ABS.

Replace the bleed nipples, old rusting ones have a habbit of rotting away to the point of unremovability if left to fester.
 

television

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I did not know that you were doing the disc as well.

Do clean and sand off any rust on the hub where the disc bolts up to. The new disc will have a rust preventer on them and this should be wiped off with a spirit. failure to clean this off can clog the pads, and cause hot spots and warping of the new disc, then a light sand when they are fitted on both sides to remove any grease from you hands.

Do not over tighten the holding screw, it is just that and stops the disc from moving when changing a wheel
 

television

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Thank you

Off to the stealer for some nipples

They will be of no use if they break off, so use the correct spanner, they are very soft. gently rocking the spanner will give an indication of their tightness
 

teddycatkin

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Hi Tony --mine were done last year the grey primer soon disappears when running .just leave it on-good luck.
 

jibcl500

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Thank you

Off to the stealer for some nipples

Mercedes barke pad paste part number A 001 989 94 51, I use it on the back of the pads where contact is made from either the caliper or piston, I also put a wipe on the edges on the pad as sometimes I have to sand the paint off the edge for better fit, if there is a crusty rust chip it away with shape screw driver and get it smooth as possible, I always smear a little greas on these contact points also to try to stop the rusty.

Do the job well and the brakes will feel great, if the piston doesnt move well it might be worth reconditioning the caliper.

Bleed nipples are 9mm, and a good 9mm flat edge socket will undo them.

jib
 
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The Crooner

The Crooner

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Job done

Threw away some reasonable discs and pads because the job had not been done properly last time, and one of the pads on the drivers sides was stuck.

Cleaned up the areas very carefully and paid special attention to the pad housings within the calipers.

Cleaned the abs reluctor rings and got the residue off the sensor.

Didn't have time to get to the dealer, so no new nipples and MB grease, but very carefully applied copper grease

Measured the disc run out at less than 2 thou, so not much wrong there.

Checked the ball joints, even though the MOT tester said they were fine, which they are, so regrettably I can find anything to do at the front end of the car.

Checked the exhaust mountings as per the MOT advisory, and I need to go and relieve the dealer of some hardware and rubber.

I do keep looking at all those rubber bushes in the front suspension, and I can find no reference in the service history to a front shock change. I just keep wondering how much better it would be if they were all changed.

The anti roll bar bushes are less than one year old.

Thanks for all the help, need to put some miles on now to get the new pads bedded in.
 


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