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Old 14 Apr 2004
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BMW GS brake upgrade - 4 and 6 piston etc

Continuing a GS front fork thread that got off track and onto brakes...

My G/S stock front brake was like all of them - pathetic. So I added a 4 piston caliper from Performance Machine, and a K100? disk - 40 mm I think bigger than stock. Big improvement, but eventually I decided to upgrade the forks as they were pretty poor, and I figured I might as well upgrade the brakes while I was at it.

So I got a 6 piston caliper, also from Performance Machine.

I also got a 320mm disk with R100GS carrier from M.A.P. Engineering which is a straight bolt-on. On the old setup with the K bike disk, I had to make a spacer to adapt it, simply spacing it out enough to meet the caliper, and although the bolt circle diameter was the same, I had to redrill the mount holes, which - of course - were a different number and pattern. Overall pretty easy.

Mounting the 6 piston caliper is straightforward on an R100GS front fork. I had Andy Miller helping, as he was on his round the world trip at the time and visiting us, so he got to do a lot of the grunt work. Thanks Andy!

A piece of thin aluminum with holes carefully drilled to match the caliper and another piece to match the forks were carefully slid into alignment and clamped, then the holes transferred to a piece of 3/8" aluminum plate. It's a good idea to wrap the bolts with masking tape so that they are a very snug fit in the holes of the templates, forks, and calipers, ensuring you end up with a perfectly aligned plate, not one with all the holes at the limits and a bear to put together.

Note that Performance Machine says a 1/4" plate is adequate, and indeed that's what they supply with the caliper for many bikes. Being a strength nut, I went for 3/8. The caliper had to be spaced in to align correctly, so I had a couple of simple spacers made on a lathe, $30. Other than that, we used a drill press to drill the holes absolutely square, and a hacksaw, files, belt sander and a good vise.

I also used high grade, 10.6 I think, 10mm bolts and matching nylock nuts.

Here's a pic of the supplied plate (for a Harley) - Top - and the first prototype of the mount plate, Bottom. Slight misalignment, about 1mm, so I went for another one - and you get to see this one!

Final installation here:

I tried the master cylinder I was using with the 4 piston, but it was way too soft, so tried another one I had - too hard, but useable, so I ran it for a season. I now have one in between - 14 mm - to try next.

There's a couple more pics and bike info here.

The 6 piston is a huge improvement over stock, and well worth it in my opinion. Any more and I'd be seriously worried about overpowering the front tire.

I also used a one piece braided stainless brake hose from Russell. They make them in many lengths and fittings, and you should be able to get a perfect fit easily.

Note that it IS possible to get a special fork leg and brake kit from HPN, but I think the added weight isn't worth the difference in braking, if any, over the 6 piston and 320mm disk. And it's probably more money by the time you're finished.

Any other experiences, questions, comments etc welcome!

Grant Johnson

Seek, and ye shall find.


One world, Two wheels.

[This message has been edited by Grant Johnson (edited 13 April 2004).]
Grant Johnson
Seek, and ye shall find.

Inspiring, Informing and Connecting travellers since 1997!

Last edited by Grant Johnson; 29 Aug 2006 at 16:48.
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Old 7 May 2004
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I seem to recall that Motobins in England will set you up with a used K-100 caliper and an adapter plate for an R-100 GS at a very reasonable price. I haven't tried it, but it's supposed to be a big improvement.
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Old 8 May 2004
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I think you'll find that Moto-Bins no longer ship to North America, possibly due to liability laws?

There's a similar disclaimer in the latest Sherlocks catalogue.

My photos: www.possu.smugmug.com
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Old 10 May 2004
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Hi Grant!

That's a serious front brake for a G/S, you must be taking up competitive riding again....

I have the Motobins 4 pot caliper conversion on my GS and it just eats brake pads at over twice the rate of the standard caliper. That's with plain vanilla, 'standard' compound pads, no fancy stuff.

I got bits of old lorry clutch plate araldited onto some backing plates in Cambodia for about $3 when I got caught out. Stops the disk from being scored, but won't stop the bike. Another lesson learned...


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