Need an idea on a problem. Have a sinking brake pedal on my 2003 MINI. Replaced the master cylinder and that made the brake firm and positive but after holding the brakes on for a few seconds the pedal sinks another inch or so then holds fine. Anyone have this problem? Replacing the master cylinder did not fix the problem,

 

Forgot to add this part-- Before changing the master cylinder there was no leaks or loss of brake fluid. I thought I read some where issues with the ABS module could cause this.

 

In the past, when this happened to me, I found there was still a bit of air in the lines or the master cylinder was faulty and passed a bit, needing to take it back for another.

 

Odd that in my case have the same out come with both master cylinders. One other thing is my DSC light is on and will not go out.

 

If this was an issue with both master cylinders there is other issues to attend to.

Have you checked all of the lines for leaks? To each of the 4 corners, front to back, then also checked that the slave cylinder isn't failed and drawing air in?

I would recommend getting a quality scan tool on the car to see why the DSC light is on, do you have a red BRAKE light on as well?

 

I'm a tech of over 30 years and do not think this is a air issue. when you have a air issue you have a spongy pedal from the get go and this is not the case. The pedal is firm and accurate then goes down a little.

 

has any one had the DSC cause a sinking brake pedal?

 

Waiting on an answer for Pelican Parts on this one.

 

No red light on, good firm pedal and stops straight and accurate, just sinks a bit when you hold it. If you can help on this I will make it worth your time.

 

Tried another master cylinder, same result! Can a defective DSC module cause a sinking brake pedal? HELP! This is driving me nuts!

 

How much does the peddle sink?

On my MCS the brakes stop no problem with the required force. If I sit idle at a light after a bit time I can press the brake peddle down another half inch or so. My whole brake system is stock with no upgrades so this migjt be normal.

 

inch and a half.

 

Okay, scan the system and found a 5E20 pressure 1 code after clearing all the old codes I knew about. Any one have this? Is the pressure sensor 1 on the master cylinder or the ABS assembly? This is why the DSC light is on, is this sensor replaceable?

 

Does anyone have a 34526759133 brake sensor? One other question, the scanner read brake pressure one. Is there more then one, if so where and where would one be?

 

Searching by the above part number shows that the sensor goes on the bottom of the master cylinder. Here is the page I got the info from https://www.ecstuning.com/b-genuine-...r/34526759133/

 

Ordered one, hope is the reason the master cylinder is bleeding off the brake pressure.