brake failure !!

[steveb]

Pedal goes to floor...calipers work fine .... bled brakes ...... diagnostic also.....

....then today !!!!...... Had the master brake cylinder changed cos all fault was
now pointing in this direction............NOW THEY DO NOT WORK AT ALL !!

She is now in a garage ( had to catch a lift home )
The garage is waiting for thier 'technical' dept in bmw to get back to them ....

The finger is now pointing at the 'DSC / ABS' control thingy box (part no. 34.51.6.773.013 )

So far it has cost almost £400 with no final conclusion and no X5 !!!!

To re-cap ..... pedal to the floor
................... rear brakes do not engage
................... gone through a set of front thrust arm bushes
................... calipers are not seized
................... Bled the brake system, including today, now three times
................... diagnostic shows a blank ( so cannot be electrical )
................... fitted a new Brake master cylinder...no change
....................even worse now.... pedal flat to floor and no brakes !!

............................. no car

Any ideas ?????


_________________
If Life Was Meant To Be Easy, Michaelangelo Would Have Painted The Floor

[Weasel]

I'm wondering if they properly bench bleed the master cylinder... I recently had to help a guy at work who installed the brake master cylinder on an X3 and didn't properly bench bleed it. It's brake pedal went to the floor even after performing the full system bleed including DSC with activation through the tester etc. I ended up going over to the X3 with a 90 degree curved end prybar (ladyslipper) and simply pried between the brake pad's metal backing plate and the rotor to compress the caliper on each of the 4 wheels. This pushed brake fluid back up into the master cylinder and knocks the air out of the valving. Believe it or not that is all it took at that point to restore full braking function.

Sounds to me like a tech with very little experience in braking hydrolics is working on the X5... that sucks but can be fixed. Before putting out any more money I'd ask to have it re-diagnosed by a tech with more experience, or to have the shop foreman assist the tech in diagnosis. Say it nicely, but tell them you aren't paying for guesswork but require proper diagnosis on such an important system with such expensive parts.

[JCL]

I would agree with it likely being a bleeding problem, either with the master cylinder or in the ABS controller. While it could be the ABS controller, the suggestion to ensure you have a good technician on it is a good one. If it does turn out to be the ABS controller, you should be asking them whether you really needed the new master cylinder (which would be a reasonable conclusion) and how they are going to charge/credit you (taking some responsibility for the components they replaced on the way to finding the right one).

[Weasel]

And thinking about it, there isn't any kinda valving in the DSC hydrolic unit that could fail causing the pedal to go to the floor... especially without causing any kind of palusibility fault through the DSC pressure sensors. Don't let them sell you a DSC hydrolic unit, they just can't have the master cylinder bleed properly yet.

[Laurence]

OK, going through this logically:
If there was a "blockage" caused by the ABS unit, you wouldn't be able to bleed the rear brakes at all. There would be no way of getting fluid to bleed from the master reserviour to the rear calipers.
The fact that they have replaced the master cylinder and now the brakes don't work at all must point to it being a master cyliner issue. Lets face it, the only pressure created in a braking system comes from the master cylinder and as I mentioned in my other post, this is a dual circuit system. So, for none of the brakes to work now does seem to point to either - the new master cylinder isn't working at all (unlikely) or there is air in the system.
I agree with the above posts - brake bleeding can take time and effort especially if you do a major repair such as the master cylinder. It is very easy to re-introduce air into the system if you are not methodical. If you use a manual method (i.e. pumping the brake pedal) to bleed the brake, you can very easily introduce air e.g. if you don't keep an eye on the fluid reserviour and let the level fall low. If this happen you'll get a whole load of air in the system. I always prefer to use a possitive pressure system where fluid is pumped through the braking system (like this one Gunson | G4062 | Eezibleed Kit). I have no idea what BMW use.
As Weasel said, air can get trapped in all sorts of places and can cause all sorts of problems to the uninitiated tech!

As with all these things I/we could be wrong, but logic tends to point to bleeding now.

Please keep us updated as to what happens.

[steveb]

thank you again all for your help...... will update this evening

[steveb]

ok..... for all those still interested....here it goes ...

Took all your advice to the garage this morning to try and
help out !!

When i got there they had heard from bmw technical who said it probably could be the servo and not the dsc ??

The garage has done a 'vacuum test' on the servo which has shown that it is holding the pressure so no leakes there !! (hope this makes sense)

So tommorrow morning they are going to do what 'Weasel' has said about using a 'ladyslipper' on all 4 wheels at the same to 'squeeze' out any remaining chance of air/fluid in the valves.....

I forgot to mention also that last wed i fitted vredesteines wintrac4 xtremes all round ready for the autumn/winter......here in West wales it has been blue skies and so sunny since then !!...... I jinxed it i think

[Weasel]

Originally Posted by steveb

So tommorrow morning they are going to do what 'Weasel' has said about using a 'ladyslipper' on all 4 wheels at the same to 'squeeze' out any remaining chance of air/fluid in the valves.....

Hey! Don't roll your eyes at me!

With any hope that is all that it needs and the brakes feel back to 100% after.
(which is more likely than you think)