Matt865 Posted December 7, 2023 Share Posted December 7, 2023 Hello everyone, I am experiencing a significant issue with the braking system in my estate. While driving, the brakes appear to function properly. However, when the vehicle is stationary and I apply pressure to the brake pedal, it gradually loses effectiveness. I have already had a new master cylinder installed and the system has been thoroughly flushed and replenished with fresh fluid. Despite these measures, the problem persists. The ABS unit does not indicate any faults. I am curious if there is anything I may have overlooked or if anyone has any suggestions regarding the potential cause of this issue. Quote Link to comment Share on other sites More sharing options...
AMG33D Posted December 7, 2023 Share Posted December 7, 2023 It is possible that there is a vacuum diaphragm leak either on the brake booster or its supply. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Thank you, friend. I will verify that. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Do you own any schematics illustrating the configuration of the vacuum pipes? Thank you. Quote Link to comment Share on other sites More sharing options...
AMG33D Posted December 7, 2023 Share Posted December 7, 2023 https://mercedes.7zap.com/en/eu/fg/car/c-klasse/c+180+cgi+blueefficiency/61s/204249/fg/0/0/42/0/060/0/0/ from https://mercedes.7zap.com/en/eu/fg/car/c-klasse/c+180+cgi+blueefficiency/61s/204249/fg/0/0/42/0/ Quote Link to comment Share on other sites More sharing options...
clk320x4 Posted December 7, 2023 Share Posted December 7, 2023 Are you referring to the concept of diminishing or declining? Was the master cylinder bled before to installation? Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Thank you for your brilliant input, buddy. I will examine it again tomorrow, specifically focusing on the whole vacuum system. Additionally, I have already tested the vehicle on the brake tester at the garage, and it seems that just the rear brakes are experiencing fading. Do you have any other information that might provide insight into a potential solution? Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Yes, the bench bleeding process was performed. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Apologies, I intended to say "falling away". Quote Link to comment Share on other sites More sharing options...
clk320x4 Posted December 7, 2023 Share Posted December 7, 2023 Question the possibility that the servo is the source of the issue. Have you activated the ABS unit throughout the bleeding process? Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Yes, the task has also been completed. I performed a bench bleeding procedure on the cylinder, installed it, and then eliminated air from the pipes leading to the ABS unit. I thoroughly examined and bled all the nipples in the right sequence, ensuring that there was no air present in any of the fluid lines. Despite these efforts, the issue remains unchanged. When I am driving the vehicle, the brakes function flawlessly. However, when I come to a halt and press the brake pedal, it remains up for a brief moment before gradually descending. Quote Link to comment Share on other sites More sharing options...
clk320x4 Posted December 7, 2023 Share Posted December 7, 2023 I own a less severe variant of the condition you have (non-MB), which I ascribe to the absence of cycling the ABS throughout the process of bleeding (since I have not yet obtained the suitable scanning instrument required). In a recent discussion on this platform, an individual proposed that this pedal action is quite typical. None of us seem to have any issues with the actual braking performance. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 I have previously encountered similar issue, my friend. However, my vehicle did not pass its MOT due to this problem. Consequently, I am uncertain about the appropriate course of action, since the issue persists when I am driving. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Their functionality is flawless, but they fail to meet the requirements for a MOT certification. Quote Link to comment Share on other sites More sharing options...
clk320x4 Posted December 7, 2023 Share Posted December 7, 2023 Locate the MOT Tester Manual online and carefully examine the section pertaining to brakes. If the brake performance meets the necessary standards, it is unlikely that a failure can be declared only based on the pedal feel, until the pedal reaches its maximum limit. Quote Link to comment Share on other sites More sharing options...
CheresX Posted December 7, 2023 Share Posted December 7, 2023 What specific issue caused the MOT failure? Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 The pedal is experiencing bottoming out, where it reaches the green zone when stationary and then gradually diminishes to zero. This issue was identified by the MOT tester. Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 Quote Link to comment Share on other sites More sharing options...
Matt865 Posted December 7, 2023 Author Share Posted December 7, 2023 I have replaced the master cylinder, and the situation remains same, my friend. As I have previously said, while I am driving, it functions perfectly. Quote Link to comment Share on other sites More sharing options...
clk320x4 Posted December 7, 2023 Share Posted December 7, 2023 Evidently, there are problems with the back brakes. Have they been arranged in order and does the issue with the pedal continue? Quote Link to comment Share on other sites More sharing options...
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