That is interesting...... my dealer tried on the "the price is due to you having the performance package.... I did protest at this as I looked at mine and a std one in the showroom when I bought it and could not see any difference between the rears at all, where as the front differences were night and day. I managed to get a further £70 off now, the bill stands at £525 inc tax for the replacement of the rear discs and pads. The service director assures me that it is normal to expect to replace the rears between 20k and 30k miles depending on how much I use the 'hold' feature and how much traffic I'm in and how hard I drive the car... as I tick the box for being at the wrong end of all 3 for economy ideals, I guess at 21K miles, it's normal.
The rear discs/rotors are not composite like the front ones, so there is another difference too.
In response to an earlier criticism/reply, he also ensured me that rear rotors and pads are ALWAYS replaced together on the 55 R172.
Interesting indeed. I'm at 50K (km's) and never had to replace anything on the brakes yet. Maybe I'm a wuzz driver, but I will inspect pads and discs next time I'm taking things apart. That will be in a couple weeks when I will install the rear radars for the blind spot assistant. Rear bumper has to come off for that so no biggie to take the wheels of for inspection.
Can't you push the bill to the next owner since you're considering a GLA45?
This IS becoming an interesting subject. WIS (workshop manual) doesn't list the values for the 55 (type designation: 172475) when to replace the disks. For all other R172 models they list them in the same sheet as the R171 models.
Tracking the disk part number A1724230112, it seems that both the 176052 A AMG and 117352 CLA AMG also use these rear disks. Back to WIS shows that on these cars the values are also NOT listed! All other models from the A and CLA series do have wear limits but not the AMG one.
What is going on? Are AMG rear disks exempted from wear limits? Than how could your dealer state that 85% is already gone?
From the internet prices for these disks vary between 110-160 EUR a piece.
If you can, I'm very interested in the thickness new of these disks and what they consider the wear limit.
For the fronts I found that the thickness new is 36mm and the wear limit is at 33mm with the wear limit upon inspection at 33.5mm. These disks are used at a host of AMG models. (like the 230472 SL55 AMG)