Hi guys,

Back again! My K100RS has a K1100 4 pot caliper conversion (done by a previous owner). Since taking ownership the master cylinder has always leaked so I have replaced it. The brake components had been taken to pieces/calipers stripped of paint/repainted and cleaned.

Since refitting everything I am having trouble bleeding the brakes and getting a 'hard feeling' on the front brake. I'm using a mityvac brake bleeder which is getting all the air out but still a spongy feel at the lever.

Is the combination of these non standard calipers a good idea? The brake pads are new by the way! New fluid too!

Any ideas???

Thanks Kim

By judging the picture you got a 13 mm master, the four pots use a 20 mm.
That could be some of the reason.
I think Rick have some experience with that combination.

That was our GITH but I have heard that a 16mm of the very last of the airheads is a good master cylinder as the brakes come up well and with good feel but the 20mm one is the OEM.
Go over your brake lines to make sure none are expanding or getting big bubbles in the outer sheath. Also if you can use the stainless braided lines they are really good.

If don`t remember wrong (which I do quite often) it recently was someone with a ~similar problem in here, in the end it turned out to be non genuine shims fitted between pistons/pads that was flexing.
Just mentions it.

Yeah I do remember that but I can never find those posts.
It was some anti vibration pads to stop squealing. They were between the piston and steel backing of the pads and once removed all was good.

Yeah, all that time which is used for searching for old posts...............................
could be used for something else................
I always find out...after.

I would be going out for a ride but I am waiting of news on my brother. He was on an adventure trip from Vladivostoc to the western europe and some old idiot ran him of the road in siberia somewhere and he is being airlifted back to Australia to get the neccessary surgery done to a busted left leg. I spoke to him via skype in the hospital in Siberia ( I haven't figured out exactly where yet) and he didn't want it done there because as he said when he went into the hospital he was given a pair of slipon plastis shoe covers and as he said they were to stop the germs getting to him not to stop then comming from outside into the hospital.

Sorry to hear about your brother, Rick.
Hope he soon get back from that remote place and have his recovery at a safer place.

Hi guys,

You were right...I replaced the four pot K1100 calipers with the original Brembo two pots and now I have a hard brake lever! Seems like the original 20mm master cylinder just isn't good enough to power the four pots!

You guys are awesome! Thanks so much for your expertise!

Kind regards Kim

KJB wrote:Seems like the original 20mm master cylinder just isn't good enough to power the four pots!

Nice that you got it sorted.............by judging the picture you got a 13mm master.
If you had got a 20mm...it would have been well suited for the four pots.

Guys
I had a similar experience and decided to hang the caliper assembly upside down for the night to get any possible air bubbles out. I also tied the brakes and most of the problem was cured. I then re bled the brakes that cured the problem. It seem that air were trapped in bottom of the assembly!
I hope this solve your problems as well
Nice riding

Rick G wrote:That was our GITH but I have heard that a 16mm of the very last of the airheads is a good master cylinder as the brakes come up well and with good feel but the 20mm one is the OEM.
Go over your brake lines to make sure none are expanding or getting big bubbles in the outer sheath. Also if you can use the stainless braided lines they are really good.

A 16mm R65 master cylinder works well with two four pot Brembos, but the 20mm K11 master cylinder works the best. Did it to my K100RS when I swapped to the four pot Brems. All K1100 and R1100 use the 20mm M/C, with or without ABS. Yessir.

Guest in the House wrote: All K1100 and R1100 use the 20mm M/C, with or without ABS. Yessir.

Just would like to add to the list.....................K100RS4V and K1.

We would be remiss if we did not also mention that 20mms were also used on the venerable R850R, but only in its early incarnation, pre-R1150. Pedants R Us. It naturally occurs around BMW owners, I have observed.