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Registered 2005 SLK55 AMG
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I recently posted a Thread covering how I changed my rear Brake Discs.

I thought I would post this follow up thread as I wondered if other owners had found their Discs to be in the same condition as I did.

The reason I changed them was because, some time ago, when the car had been in for a Service, the front Discs were reported as having 30% wear but the note for the rear Discs just said “Corroded%.” with an Advisory Note saying “Requires rear discs/pads”. The easily visible, outer faces of the Discs didn’t show any corrosion but to enable me to check the inner face I removed a rear wheel and the pads. It was then possible to get a limited view of the inner face of the Disc. There did appear to be ridges on this face but with only the poor view available I couldn’t see any corrosion. However I set about researching what Discs and pads to buy. I settled on a pair of Original M-B Discs and pad pins (£495 inc. VAT) but bought my set of Pagid pads from Eurospares (£38-50 compared to M-B Pads at £128-40)

For various reasons, principally the fact that the brakes gave no sign of having any problem stopping the car, it was some months before I had time to begin the Disc change. When I finally got them off I was shocked at the condition of the hidden faces of each Disc.

As the Back Plate shields any clear view of the inner face of the disc it wasn’t until I got each of them off that I could have a good look at them. What surprised me was that I didn’t just find wear ridges but that, when I had removed both Discs, their inner and outer faces had an identical problem.

The outer faces were both worn smoothly but the outer half of the inner faces were both covered in in a layer of Brake Pad material.

The first photo I have included shows one of the outer, easily visible, faces. As can be seen these gave no hint of a problem.

The next photo shows the inner face of a Disc, with its covering of pad material.

The third photo shows a pair of Pads from one Disc. The Pad on the left shows where the Pad material has been stripped from it compared with the smoothly worn Pad on the right, which was in contact with the outer face of the Disc.

The final photo shows a closeup of the inner face of one of the Discs after I had picked off a small area of pad material . This could be done with a finger nail as it wasn’t firmly adhering to the rust pitted surface of the Disc.

A few other facts before I finish which may be helpful to anyone who could shed some light on what has caused this situation to have happened:

This layer of Pad material has a max thickness of only about a third of a mm.
The smoothish surface of the Pad material layer brought its level to that of the metal Disc.
The width of both Discs, between inner and outer faces is approx. 25mm. Well within normal wear limits.
 

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Premium Member 2005 SLK350
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3,730 Posts
I recently posted a Thread covering how I changed my rear Brake Discs.

I thought I would post this follow up thread as I wondered if other owners had found their Discs to be in the same condition as I did.

The reason I changed them was because, some time ago, when the car had been in for a Service, the front Discs were reported as having 30% wear but the note for the rear Discs just said “Corroded%.” with an Advisory Note saying “Requires rear discs/pads”. The easily visible, outer faces of the Discs didn’t show any corrosion but to enable me to check the inner face I removed a rear wheel and the pads. It was then possible to get a limited view of the inner face of the Disc. There did appear to be ridges on this face but with only the poor view available I couldn’t see any corrosion. However I set about researching what Discs and pads to buy. I settled on a pair of Original M-B Discs and pad pins (£495 inc. VAT) but bought my set of Pagid pads from Eurospares (£38-50 compared to M-B Pads at £128-40)

For various reasons, principally the fact that the brakes gave no sign of having any problem stopping the car, it was some months before I had time to begin the Disc change. When I finally got them off I was shocked at the condition of the hidden faces of each Disc.

As the Back Plate shields any clear view of the inner face of the disc it wasn’t until I got each of them off that I could have a good look at them. What surprised me was that I didn’t just find wear ridges but that, when I had removed both Discs, their inner and outer faces had an identical problem.

The outer faces were both worn smoothly but the outer half of the inner faces were both covered in in a layer of Brake Pad material.

The first photo I have included shows one of the outer, easily visible, faces. As can be seen these gave no hint of a problem.

The next photo shows the inner face of a Disc, with its covering of pad material.

The third photo shows a pair of Pads from one Disc. The Pad on the left shows where the Pad material has been stripped from it compared with the smoothly worn Pad on the right, which was in contact with the outer face of the Disc.

The final photo shows a closeup of the inner face of one of the Discs after I had picked off a small area of pad material . This could be done with a finger nail as it wasn’t firmly adhering to the rust pitted surface of the Disc.

A few other facts before I finish which may be helpful to anyone who could shed some light on what has caused this situation to have happened:

This layer of Pad material has a max thickness of only about a third of a mm.
The smoothish surface of the Pad material layer brought its level to that of the metal Disc.
The width of both Discs, between inner and outer faces is approx. 25mm. Well within normal wear limits.
condensation forms between the disc and back plate when the car is stood overnight causing surface rust . the front of the disc is not effected as air can flow around it unrestricted. also washing your wheels and then leaving the car stood till the next day or longer before you use it speeds up the rusting
 

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Premium Member 2008 SLK55 AMG "Mabel"
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15,377 Posts
Leaving your car sat unused outside for even short lengths of time can cause the discs to rust. I have to leave mine for 2 - 3 weeks when I go off shore, allowing the rust to build up, and every car I've had has had shortened disc/pad life spans due to this. :frown:

On the bright side, the solution is to get out and drive it every day. :smile:
 
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