Master cylinder change ?

alex said:

It sounds similar to my M/C failure. The more I used it the longer the travel, however brake fade (boiling fluid) is a thing too and you need to be sure that its not that.

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Boiling fluid? And how can I see that its not that?? When I purgue the liquid the master cylinder works ok, but only with one day of use the moto in curves, the smooth lever begins.

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You know about brake fade I assume? Brake lever travel gets longer when the fluid gets hot (reduced viscosity). It then returns to normal at lower temps.

If it was this I?d suspect the fluid was not up to spec.

However, i think at least testing another MC would be a good idea.


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I thought that the lever travel was a bit excessive on my 15 for the first two years of ownership, which included the brake fluid change at the 12K service. Then one day I dug out my trusty Mityvac and hey presto, nice firm lever!

What is mityvac?
I had put new dot4 one month ago, after that the lever was very hard, I ride out for some turns with my friends and the lever became smother and smother and now is like before changind the dot4.

I dont know where is the problem.

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A Mityvac is a vacuum pump designed to suck air out of a brake system. It's a very useful bit of kit!

snooker said:

A Mityvac is a vacuum pump designed to suck air out of a brake system. It's a very useful bit of kit!

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My bmw was changed liquid a month ago, when leaving the workshop the touch was very hard but with a single day of curves and is soft again and that is how it is.

Master cylinder problem?
I need better brake fluid?

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It's possible the liquid used in bmw is not very good, when I go out from de mechanic the lever is very strong, very very strong, and only after few km in the street it begin smoother and smoother, and now I need to use lever in position 1 because if I put the lever for example in position 3, I brake with 2 fingers and break my other two fingers with the lever.
https://youtu.be/S9NMe27hqb8

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Good video.
OK. You could try Brembo LCF600 fluid, even my Brembo RCS19 improved for using it.
But your lever movement is long like my rubbish OEM MC was, so I suspect you?ll end up needing to change.

Trying the fluid first won?t hurt...you?ll still want good fluid for the new MC.


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Mine is a 2010 model with abs and 34k miles, I only use it on the track and have no issues with the standard master cylinder and standard brake lines, I use a branded dot 4 fluid and bleed the brakes every pad set change as well as cleaning the calliper pistons. I currently use Goldfren s33 race pads with no complaints and such a bargain price. The static feel of the lever is slightly soft, however on the track I have no issues at all. My GSXR 1000 however was a different story, I had to fit a Brembo rcs 18 20 master cylinder as I used to lose the lever by lap 3.

Jay S1000rr said:

What?s happening at the calipers when u pull that lever like that ? Do all pods press out evenly, u can see this by the pads compressing ? I?d seriously strip ur calipers , give good service, flush ur m/c and lines with some cheap fluid, throw away. Do same for the m/c . Use some good make fluid such as Alex mentioned to refill.
Have u checked ur lines from levers to pump to calipers. See if any tiny holes sucking in, how old are the lines ? After market or bmw ?

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I took the bike two months ago to change brake pads, changed brake pads and liquid and here the problem started. The bike is from November 2015, all original.

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Jay S1000rr said:

It?s inline problem and not m/c if the problem has just arose after the swap over of pads and fluids .
Did u Strip the callipers ?

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I don't know, the mechanic changed fluid and brake pads. I think is no necessary take off calipers for change pads no?

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Ok, I have it decided.

I will take the bike to a specialized workshop in my area that works in the competitions.

I have decided that the Brembo CNC 19x18 is very expensive, with that price I can put the Brembo PR 19x18 and also change calipers for the M4.

The M4 are better than the original gold calipers?

Is it better to change calipers or discs before?

Thank you.

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M4?s 32mm/32mm pistons, will need different pads, but yes they are an upgrade.
They need different length of lines (HP4).

Al long as the discs are Brembo ORO or better they will be fine.


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alex said:

M4?s 32mm/32mm pistons, will need different pads, but yes they are an upgrade.
They need different length of lines (HP4).

Al long as the discs are Brembo ORO or better they will be fine.


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Different length of lines? Why if the calipers have the same size?
I think is not necessary to change brake lines changing m/c and calipers with 100mm between holes.

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They have a different line mount point/orientation

@Towers040 on here has been through it.


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alex said:

They have a different line mount point/orientation

@Towers040 on here has been through it.


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****, you just trashed my plans. Changing lines is a pain in the ass.

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Yeah brake lines need changing to fit the M4?s as the originals are slightly to short also the banjos are different and cause the original s1000 lines to run the mudguard and tyre


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towers040 said:

Yeah brake lines need changing to fit the M4?s as the originals are slightly to short also the banjos are different and cause the original s1000 lines to run the mudguard and tyre

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Click to expand...

Also fitting the hp4 lines is a pain and so much easier if you just get a new set of hel/venhill lines


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Jay S1000rr said:

But what if the issue is ur lines as I pointed out previously.
U spending a lot of money to have the same issue considering u already stripping everything down.

Do U ride on the road and circuit or just circuit ?

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Road 25% circuit 75%

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Jay S1000rr said:

Sorry I can?t see what year ur bike is ?

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S1000rr november 2015.

I had decided to change calipers and m / c (M4 + PR), and review all possible vanishing points in tiling, but not change the lines, that is a pain in the ass.

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