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Discussion Starter #1
My brakes have lost their confidence recently, maybe over the last 6 months ... it's been gradual.

Ultimate stopping power isn't there and the pedal has a fair bit of travel to get them working properly.

We spent a solid hour bleeding the brakes last week, starting closest to the master cylinder then following it diagonally. "Normal" Dot 4 fluid from the motor factor (I couldn't get any Motul ordered in time) - but we used an entire litre to flush anything old out of the system before finishing the bleed.

They still feel terrible :confused:

I demand good brakes - my other cars have AP Racing brakes and extreme pads with solid pedals and I remember a time I also had this with my M5.

I've brembo disks and Ferodo DS2500 all round, so unless it's the case that the pads have changed in their composition as they've aged, there is something else wrong.

There is plenty, and I mean plenty of compound on them and the disks have no lip - we replaced disks and pads all round last summer before the 'ring.

It's not a sticking calliper as I've hand-checked how hot the brakes are after a steady run, and also I replaced the front callipers with a much better condition set late last year as well.

All I have left to consider is the master cylinder - is there a straightforward way to check?

If it is finished, how hard is it to replace (bearing in mind we can do most things here) and what are my options for replacement?

Many thanks!
Stephen
 

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Hi
Best practice is to bleed brakes by starting furthest bleed nipple from master
cylinder.
I bleed 4 & 6 pot calipers in parallel on each side, ie both nipples on each caliper open.

If bleeding by this method not working, you may have some air trapped in lines to ABS modulator valve.

I would check the whole system for obvious leaks.
If master cylinder going = little resistance when when brake pedal is depressed.
Look for signs of master cylinder seals purging down the back of the brake boost servo.
Some times the master cylinder piston partially seizes , not allowing full hysteresis.

Cheers
 

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Discussion Starter #3
Thank you - I'll check all that out, including the ABS stuff, I'll go read the service manual around that to make sure we know what we're doing!

I sadly only have the earlier 3.8 brakes (i.e. sliding piston single pots) - would you still bleed the same way as you're saying for the bigger brakes?
 

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I'm having the same problem. I just replaced the single piston calipers with a set of boat anchor 750iL ATE 4 pots. I've spent 2 hours bleeding with 0 bubbles, but the pedal goes to the floor with the whole system closed.

HELP!!!

I'm thinking that there is a large enough air bubble that the piston travel in the master cylinder is not compressing it enough to move it anywhere in the line. how should i get the brakes tight again?

I've heard that multi piston brakes are harder to bleed, so what's the trick to getting that pedal hard again?
 

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I sadly only have the earlier 3.8 brakes (i.e. sliding piston single pots) - would you still bleed the same way as you're saying for the bigger brakes?

Yes, you always want to bleed your brakes starting from the farthest away from the master cylinder, then the next furthest, and so on until you're done. Doesn't matter if you've got single or multi-piston calipers. Always need to start furtest out and work your way in.
 

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Stephen,

I had the same problem earlier this year - air trapped in the system.

- In February, I decided to sharpen-up my brake response and bleed the system out - prior to attending a Track Day at Donington Park, the following day.

However, unlike previous successful jobs, I simply ended-up putting more air into the system. I couldn't bleed the system out successfully, despite several repeated attempts. The pedal was going straight to the floor - I had barely no stopping power at all. I re-bled several times (late at night in the end - and with the help of Jon Baker Jnr), but to no avail. In the end, I had to concede failure - and had to leave the ///M behind, and took a Z3m instead. :grrrr:

Took the car to a dealer and they said the ABS System was full of air. :grrrr::grrrr:.

Had never got it wrong before - so I can only assume my one-man brake bleeding valves had developed a fault, letting air back into the system. Or human error on my part.....:crying2:

I been thinking for a month or so now that my master cylinder may also be the next part in line for replacement on my ///M - The brakes work fine - but there's always about an inch or so of dead play at the top of the pedal, and it gradually gets worse after arduous use on the track - although the brakes do always work fine.

-- It's most-noticeable after I get out of my Audi A3 - which being a newer car, has no dead-play at all on the pedal at all.........:rolleyes:.

What's the cost implication of replacing the Brake Master Cylinder ? - my car's done 96k miles / 13years old - is this an acceptable / expected period for failure ? - Is the failure a gradual loss of braking efficiency, or more-instantaneous failure ?

Apologies for answering this thread with more questions than answers !
 

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Discussion Starter #7
No apologies TK, exactly the type of discussion I want!

Interesting, I'll have to research how to bleed the ABS system, because it does sound very similar!

I have a long pedal, but it never gets to the floor (or as bad as yours was) ... ABS seems to occassionally cut in quite prematurely (which it never used to do), so that also looks promising to diagnosing the problem.

Thanks mate ;)
 

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Stephen,

I had the same problem earlier this year - air trapped in the system.

- In February, I decided to sharpen-up my brake response and bleed the system out - prior to attending a Track Day at Donington Park, the following day.

However, unlike previous successful jobs, I simply ended-up putting more air into the system. I couldn't bleed the system out successfully, despite several repeated attempts. The pedal was going straight to the floor - I had barely no stopping power at all. I re-bled several times (late at night in the end - and with the help of Jon Baker Jnr), but to no avail. In the end, I had to concede failure - and had to leave the ///M behind, and took a Z3m instead. :grrrr:

Took the car to a dealer and they said the ABS System was full of air. :grrrr::grrrr:.

Had never got it wrong before - so I can only assume my one-man brake bleeding valves had developed a fault, letting air back into the system. Or human error on my part.....:crying2:

I been thinking for a month or so now that my master cylinder may also be the next part in line for replacement on my ///M - The brakes work fine - but there's always about an inch or so of dead play at the top of the pedal, and it gradually gets worse after arduous use on the track - although the brakes do always work fine.

-- It's most-noticeable after I get out of my Audi A3 - which being a newer car, has no dead-play at all on the pedal at all.........:rolleyes:.

What's the cost implication of replacing the Brake Master Cylinder ? - my car's done 96k miles / 13years old - is this an acceptable / expected period for failure ? - Is the failure a gradual loss of braking efficiency, or more-instantaneous failure ?

Apologies for answering this thread with more questions than answers !
this is exactly what I'm experiencing. even before i swapped calipers, my brake pedal had a dead spot at the top of the pedal.

would a pressure bleader be able to push the air out of the ABS system?
 
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