I have the standard ABS 2-piston black calipers and I want to upgrade to the 4-piston Brembo ones, from the '93 K1100. They are not easy to find though, and when I do, they are expensive to buy! Thatswhy I wanted to ask if any of you guys might know any calipers that fit straight on the OEM rotors / disks and are compatible with the ABS and master cylinder.

Im also interested if you have a set to sell me cheap(er). Thanks a bunch!

Check this page:
Beemerboneyard

This is a reputable seller (I had bought a lot of parts from him)

Bert

Hi Locksmith,
Is there a problem with the standard K100 ABS front brake since my front brake can give all the braking I can handle and suspect (but am too chicken to try) that I could do a front wheel stoppie on my new Michelin 2CT Pilot Road tire. Have you tried alternative pad compounds? Would welcome some comments because in all the reviews I have read the K100 double disk front brake has got very positive reviews
Regards,
K-BIKE

Well the brakes are good but, apart from looks, I want to bring the stoping power as closer to today's bikes as possible. My father has never used other pads than OEM (the K is his) and when I compare the brakes to my beloved '06 SV1000S I find them harder to press and more difficult to stop the BMW. I know that the K is way heavier than my zuki but I suspect the 4-piston brembos or other calipers that fit, will definitely give more stoping power, and even if they dont, I will definitely have a better feeling on the brake lever.

Its so strange that brakes from newer BMs dont fit to our Ks.

OK Frog, thanks for the link... After I conducted a small search, I found out that there is actually compatibility with the K1200 RS / LT (up to '00), with the R850 / 1100 and with the R1150 GS (up to '01). These bikes seem to be wearing both the K1100 RS calipers (probably the early models), but also the newer 4-piston brembos with the BMW logo on the outside and the brembo on the inside. Do you guys reckon these newer calipers will work 100% on my ABS K100RS?

Hi Locksmith,
Are you able to get the ABS on the front wheel to operate at reasonable lever pressure? If the wheel has locked under braking hence triggering the ABS no additional braking is available by any lever/master cylinder combination. I understand you wanting different feel on the lever but one problem with the K is given the location of the ABS pump there is a fair bit of pipe plumbed in which will affect the feel especially the rubber brake hose parts of that. Have you considered replacing the standard flexible brake lines with something like the HEL ones which are available in Greece. They will improve the feel.
http://www.h-e-l.co.uk/info/international.htm#Greece then you could look at alternative pad types as well

Regards,
K-BIKE

No I havent locked the ABS yet on hard braking, so there's still room for improvement. The brake lever is quite hard to push and since the bike is heavy, its harder to stop as well. With the new, bigger and better brakes from the R850 and the metal brake lines, the stopping power will dramatically increase and it will definitely give my K a more modern look than the OEM 2-pistons. I dont know, it might just be me, but I really want to go through with this mod. Even though its relatively quite expensive. And I dont think the calipers interfiere with the ABS because the sensors are located on the disk centres.

Hi locksmith and firstly let me say the bike looks fantastic and it should be an interesting mod. It is something that has been in the back of my mind since I first got my K as the brake calipers at least, seem to be identical to my R100RT which was substantially lighter, and twenty plus years ago were the "ducks guts" but I would not think in the same league as todays stoppers.

I think the "curve ball' in your case is the ABS so unless someone else has done it we will only be guessing. In a non ABS system the only real problem would be matching the master cylinder to the calipers to achieve the correct braking pressure and feel.

In its simplest form the ABS should not "care" about the calipers or rotors just that the wheel is rotating or not. The ABS system should also be a closed loop so the location of the pump should not be a real issue but as suggested replacing the lines with stainless braided would take another variable out of the equation.

I can imagine though that when originally designed I would hope that all aspects of the braking system are taken into consideration so I think you are heading into some fairly serious grey areas and not something you want to go wrong at the wrong time.

From what I can gather the ABS can be turned off at will so maybe try and get it running smoothly without it and then introduce it into the equation although testing it could be, to say the least, an interesting experience.

I look forward to seeing how you get on.

Regards,

Phil

Hi Folks,
Yes this is a fascinating idea and will as has been said look really good, The only thing to consider before doing such a modification would be the attitude of your insurance company and what we call the Warrant of Fitness inspection or what used to be called the MOT in my day in the UK. The big crunch is if you were to have an accident where the insurance assessor looked at the bike and they noticed the modification it would be a great free get out of paying opportunity for them unless you have cleared it in writing with your insurer as a "modified bike". Sadly insurers are usually looking to find ways of not paying first before anything else.
Regards,
K-BIKE

Yeah the calipers shouldn't be a problem interfiering with the ABS... But what about the disks? Are the K100RS front disks same as the K1100RS? Because in the K1100RS they seem bigger. Do you know for sure? I really wouldn't want to pay for disks as well...

The insurance companies are no problem at all and they never conduct a research of this sort.

Try this link:

http://www.bmbikes.co.uk/PDF%20Downloads/K1100RSSpec.pdf

and see if it clarifies things or opens another can of worms.

Regards,

Phil

Well the K1100 with the 4-piston brembos has 305mm disk diameter as opposed to the K100 that has 285mm, meaning that i'll be needing a set of disks as well. They cost around 150 euros per set or maybe more so, my father does not want to go through with it, at least for now. He already has spare disks, pads and even a set of 2-piston calipers as well, and he doesn't want them to go to waste. Anyhoo, I will probably leave it as it is for now since my father says no, its a good thing we know that there is actually compatibility between these 4 models and among maybe more.

Don't know if you have seen this but it makes things quite clear except for the ABS:
4 spot calipers

Regards,

Phil

This is likely old news to the post at this stage but I located a pair of 292mm diametre Suzuki brake rotors mated to a pair of 4-piston Brembos from an R1150GS, made a pair of approximately 8mm thickness, 4-bolt hole aluminium offset spacers that fit between the wheel's hub and the rotors so that the discs are perfectly centred in between the 4-piston Brembos with EBC HH brake pads, and have been using them on my 1991 R100 Airhead for a coupla years.

I'm about to do the same on my 1987 K100RS. Here's a link to a happy snap of them on the bike. The fairing is a modified K1200S piece.

https://i.servimg.com/u/f69/14/79/97/16/r100ks14.jpg

Very nice and considering the K uses the same brakes as my old R100 with vastly greater weight a definite improvement without overkill.
Still using the same master cylinder?

Regards,

Phil

The custom R100's master cylinder bore is 16mm (R65) which gives a reasonable feel at the lever (with just a red pube more travel than I like) but which provides stoppie-like braking power on the olde girl with those later Brembo 4-piston calipers and K75S 'S' forks. The metal of the Suzuki discs must be of a high enough grade because it works well. The bike has good brakes compared to anything from BMW of the early dayz - it's a '77/'91 hybrid, I bought the 1977 new, it's a real bitsa. I don't know which model Zooki the discs came from as I obtained a few sets of them from a former BMW dealership work colleague who was a club racer who used them with special multi-piston calipers on his rarefied Airhead. He raced it in an American/Pacific Northwest series ten, maybe fifteen years ago. He's the one who fabricated those aluminium spacers that centre the discs right in the middle of the caliper.

There's a chart out there floating round the internet which purports to show the correct ratio master cylinder to caliper piston size. It's reasonably accurate in the ratios I've attempted on various bikes. But, I note that later K100 and all K1100 series, with or without ABS, used a 20mm bore and yet the later Airheads used a similar 4-piston caliper with a 12 or 13mm master cylinder. I don't currently have a 20mm master cylinder to try, only a 12 and a 13mm bore version, for when I do the deed to my K100RS.

One other thing that really helped when putting together the Airhead's set-up was a set of high-quality HEL stainless steel braided hydraulic lines made locally near Brisbane. It's one thing to get a bike going, we all enjoy that, and another thing entirely to yell 'whoa' and get some results.

I agree about the stainless steel braided brake lines.
The original rubber ones have the tendency to expand when under pressure.
Apart from a good set of brake pads, replacing the hoses is the cheapest mod to improve braking power.