BMW M5 Forum and M6 Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
130 Posts
Discussion Starter #1
My M5's brakes have always been fantastic.
They bite hard, and if you depress the pedal further they continue to bite-down harder and harder.
Very linear, full of feedback.
SA got the EU-spec discs, and I honestly feel that my brakes have been amongst the best of the best.
I know you guys rate your stock brakes to be rather mediocre - but I find them to be excellent.

I fitted new pads in December - OEM spec ATEs.
I measured the discs at the time with a half-decent micrometer, and they were still within the manufacturer's 1mm wear limit.
Bedded them in, drove to the middle of nowhere for a holiday.
No issues - they felt as good as ever.

Fast-forward to today.
I don't drive the M5 hard much anymore.
Tonight I had a bit of fun and noticed a big difference in braking performance.
They bite nicely at first - just as they always have.. but if I further depress the pedal, they don't bite-down any harder, like they used to and are supposed to do.
I'd say this is only noticeable under hard, progressive braking.

In December, I had some suspension damage due to potholes.
It was the wrong car to drive to the holiday destination, as the roads are known to be terrible.

Anyway, the place down in the middle of nowhere that did the repair work on the car, BSed me at the time as to the damage etc and did a dodgy job.
Long story short, the rear subframe was replaced a month ago and I've only had the car back for about 2 or 3 weeks, after 6 weeks of waiting for parts etc.

The guys that did the work recently, here back home, had to disconnect the entire rear suspension etc.
After having removed the rear brake calipers they then bled the system and topped-up the brake master cylinder as required.
The brakes were perfect before this - but now they're not right.

Could they have not bled the car properly?
Maybe they used kak quality fluid?
Or, could there simply be air or water in the circuit somewhere?
Pedal doesn't feel spongy, but it's perhaps not as "solid" as before.

Discs look like this at the moment:


Thanks M5 experts :1:
 

·
Registered
Joined
·
10,309 Posts
Have you tried bedding in the brakes again? They do look well bedded. The blue on only the inner and outer edge might be saying something, does not jump out and yell at you. Maybe the pads got put in on the opposite sides and contact is not quite the same. Is that the rear rotor, I have a step in the rear, but you have different so I have to ask? I am assuming rear because you asked rear.

Could be any of the three things you mentioned. If it was me I would bed them in again and if that did nothing I think I would do a flush and replace all the fluid. For me that is a once a year thing because of the hot and cold seasons, but I believe it is a once every two or three years under normal service anyway. No loss just maintenance.
 

·
Registered
Joined
·
130 Posts
Discussion Starter #4
Those are the fronts.
I mentioned the rear, since the rear's were stripeed etc.
The pedal definitely doesn't feel as "solid" as before.

They also replaced front lower control arms - perhaps they dis-assembled the front callipers and replaced the pads onto the incorrect side.
How do I go about bedding-in again? Normal bedding-in procedure as with new pads?

Is there a special method to bleed the M5's brakes?
 

·
Registered
Joined
·
4,896 Posts
Incorrect side shouldn't matter with respect to pads. The type of pad is the critical bit.

and if they weren't bled correctly, the pedal would feel soft and spongy.

What you describe sounds more like pad fade.
 

·
Registered
Joined
·
6,014 Posts
You could have a stuck caliper which is causing a lot of heat making the brakes fade quickly. The easiest way to test for this is to use a IR thermometer. Drive the car for a few minutes then pull over and take the temp of the rotors, each side should have a similar temp to the other side. If one of the rotors is a lot hotter than the others that is your problem area.
 

·
Registered
Joined
·
10,309 Posts
Bed the same as new it just eliminates that as a possibility. It likely is just some air or moisture. If the pads were better and now worse not likely the pads but maybe they set them on the work bench and they got dirty. Can't guess at what a bad garage might do.
 
1 - 8 of 8 Posts
Top