1985 K-bike brake upgrade

[Lawrence]

I've noticed that the four-piston Brembo brake calipers are easily and economically available as used parts.  Who knows of a manufacturer/provider of adapters that would permit mounting them on the 1984-5 K100 bikes?  Or, are the later 4-piston  BMW-branded  calipers a straight bolt-on without any adapters needed?

[Inge K.]

Then you have to take in consideration that you also must change the master to one with bigger diameter.

Inge K.

[frankenduck]

You can't just bolt on the 4V calipers.

The "easiest" way is to install an entire front end from a 4V bike.  That's what I did when I built my K75.  Forks, fork trees, master cylinder, calipers, rotors, axle and wheel.  Not only do you get better brakes but you also get a beefier set of forks that have progressive springs from the factory.

I used an ABS wiring harness and with a few mods was able to make it an ABS bike using an ABS I K1100 control unit.

When I wear out the current bias ply tires on the wheels I used I'm also going to install radial tires.

The stem of the 4V fork trees is smaller so you give up the steering damper built into the steering head of the frame but the only ill effect of that that I've noticed is that it's a little wobbly at VERY low speeds - like when you're going as slow as possible in stop-n-go traffic.  Once you get any speed at all everything rides fine.

[tg4360]

If you don't want to change out the whole fork assembly, they will bolt up but the rotor offset is different.

I saw a write up elsewhere (I'll try to find a link) where the guy figured out that a particular part number from EBC has the proper offset so that with the duel pot calipers and new rotors he was all set.

It is true that you need the new MC due to the volume change in the system.

TG

[Lawrence]

That would be very good to know TG.  It's far more appealing that changing out the entire front end of the bike.  I've been very happy with the behavior of the front end of my 1985 k100RS.  I recently put a decent suspension unit on the rear and I'm now in hog heaven.  No, not that kind of Hog....  ;)

[Rick G]

This may help it uses Suzuki discs of somr sort http://k100rt.aforumfree.com/t2713-wider-wheels-radial-tyres-on-a-k100

[DRxBMW]

I saw a write up elsewhere (I'll try to find a link) where the guy figured out that a particular part number from EBC has the proper offset so that with the duel pot calipers and new rotors he was all set.

TG

Todd Lampone is the one who inspired that idea, see below. I think it would/should work OK !

http://www.k-bikes.com/forums/showthread.php?t=18156

FWIW, when I inquired about using a different front brake on a K 75 project 3 years ago, all the expert gurus were negative about the change, citing unknown failure values as the reason.

[Rick G]

The R100R discs are certainly a better thing than the suzuki discs. Makes for a much better and easier conversion.

[rbm]

This URL:

http://k100rt.aforumfree.com/t1223-installing-k1100-front-brakes-on-a-non-abs-k100rt

for a tutorial on how I replaced the rotors and calipers on my 1988 K100RS.  Be aware that I had 4V / K1100 forks already installed on the bike but still had the 13mm master cylinder.

[tg4360]

TY DrX for finding that.

I'm laid low by a nasty change of season cold and it seems to have affected my google foo.  Heck, I'm even a member of that forum and couldn't shake the link out of the drug induced cobwebs in my head.

TG

[Lawrence]

Excellent link RBM. Thanks for posting it, and much thanks to the rider who took so much time and made such an effort to share his knowledge.

[frankenduck]

RBM: In skimming that I noticed your comment about the throttle cables being an issue.  My K75 has a complete 4V front end and I just used a K1100RS throttle cable.

[rbm]

Yes, I bought a K1100RT throttle cable, being the longest offered by BMW.  It would have been an issue if I chose to route the cable through the frame opening through which the clutch and choke cables were routed ( I did attempt this ).  My brake caliper change was in conjunction with my RS -> RT conversion.  That conversion included installing the RT bars. The former two cables were long enough such that I didn't have any problems getting enough slack out of them to guarantee problem-free operation.  The throttle cable was different.  I was not able to find a way to route that cable that would not have presented a problem with the throttle operation when the bars were hitting the stoppers.  The way I routed it (between the radiator and frame) solved that potential problem.  The odd routing is barely noticeable with the RT fairing in place.  It's been that way for more than a year now and no problem has ever appeared.

Your experience might be different.  It would be interesting to see how you solved the cable routing; there are many ways to "skin a cat" as the saying goes.

[frankenduck]

I just routed it where the K75 throttle cable would go.  Through the frame on the right side of the steering head and then over the air box to the TBs.