Current M5 Braking Problem

One of our members has a current M5 with around 20K miles on the clock. Since the car was new, he has complained that the brakes did not work properly. Seems that when they are cold, not much happens when the pedal is pressed. A few days ago the pedal went to the floor and no brakes came on. When it was released and pressed again, they worked fine. The main agent has contacted Germany and their response was that it was impossible for an M5's brakes to function in this manner. Luckily the car was only travelling at about 1mph when it happend. It has happened at least once before, when turning off the M6 onto a slip road.

Questions.
Has anyone else had problems with M5 brakes?
Is there a design problem?
Is it just an intermittant fault that is hard to find?

Your help would be appreciated.

new pads (his could be glazed) and flush out the fluid for a start anyway, although it does sound like a leakage in the servo or something more serious..

Sounds like an airlock in the braking system that has just released itself. The brake reservoir has a non return valve to allow air out, but not in. I would suggest having the brakes power bled. Cars with 4 pot callipers ie e28 M5, M635 and late model E34M5's are great, but the brakes can be a pig to bleed. Also it may be worth checking that all the bleed nipples are closed properly.

It won't be a servo problem if the pedal goes to the floor. Servo's just can't fail like that. The worst you can get with the servo is a stiff, non assisted pedal.

It's also unlikely to be an air lock. You can't have an air lock hiding in a hydraulic system. It's either there or not. If it's there, you WILL have a spongy or very long travel pedal.

Sounds to me like a leaky master cylinder or something along those lines. Mind you, the current M5 is going to have all sorts or electronics involved as well. Who knows what the DSC or other systems are capable of.

I would like to think that all these systems fail in the safe state. i.e. with the brakes still working. Maybe not assisted, or with ABS, but still have a pedal that if pushed will retard the car to some extent.

Ian.

-like others have hinted at this might be an electronic issue.

-if, for example, the ABS system decides (wrongly) its a good idea to work at very low speed the result can be a very long pedal and virtually no brakes. This has happened to me on other cars, and all it needs is ill-thought-out software and a dodgy sensor or wiring and hey presto you have an apparently big problem.

-I agree it defintely needs to be fixed before the car is used again, although if there is a fault in the ABS sensor system this should be more likely to fail safe when the car is moving at more normal speeds, as the system is better able to diagnose internal faults.

worrying though.....

 

are the pedals on late model E39 M5's "fly by wire"?

- I perhaps ought to have mentioned this before, but- I have once seen a failed master cylinder (on a motorbike, but a car one will work the same way) where the main seal was worn by scraping on the port that goes to the fluid reservoir. This happened for two reasons;

1)  the edge of the port was not dressed or radiused, just left sharp.

2) the pistons in the calipers perhaps did not retract fully, leading to a 'short pedal' (well lever actually) situation. When the brakes were applied, this allowed the seal to be under great pressure when it was still partially over the port- not something it was designed for.

The seal failed in such a way as to produce intermittently spongy and/or 'excessive travel' braking for some time. This could have become a 'no brakes' situation at any time- very worrying indeed.

If the fault described above ever occurs at any speed (esp without any indication of abs or asc operation) then I would suspect a potentially serious internal fault in the master cylinder.

cheers

 

Edited by Brucey