Rovering on ads websites, I've spotted last week a sad looking K100RS dismantled for parts, that seemed to be equipped with unusually large front brakes...

I asked the seller better pictures of the brakes:


Damn!
These are a very rare brake kit from SEMC, the Brembo importer in France in the eighties.
I had never seen it for real, just a line,about it in a vintage catalog...

So this afternoon, it was in my mailbox.
The brake disc itself is cast iron, with a much better friction power than steel brakes.
But with a tendance for corrosion...
The diameter is much bigger, 300mm, and the pad track seems wider also.
The center is made of gold anodised aluminiun, with a specific shape.


There's also aluminium plates for the calipers to compensate the wider diameter.

Also in aluminium but unprotected: sadly one is badly corroded. I think I'll have to make new ones machined.

Anyway, that will fit perfect on the new PVM rims of my eighties k100 racer.!

I'm guessing you already know this JBT, but you're going to have to hose down the wheels after every ride to get rid of the brake dust. If you don't, yes, the wheels will get corroded with ferric acid (water + rust). I learned that the very hard way on my 850-T3 California where not cleaning the wheels regularly wrote off a pair of very rare Borrani rims (find a pair for under £750? - not a chance!). I had a pair of PBM cast discs on LFB and was a bit more careful with the hosepipe this time. They still chewed the black paint off though

Oh yes - that's the same disc as was fitted to the Guzzi LeMans. To the best of my knowledge, only the LeMans had drilled discs. All others had solid ones.

I rode my 850 T3 California through a couple of salty road winters. 
My thumb still remembers 45 minutes in minus 15 deg C (With a sidecar attached)
Cast iron brake discs belong on cars and trucks.

The Moto Guzzi I often rode for a coupla years in sunny Albuquerque had cast iron discs front and rear. The 'feel' was fantastic, stopping smoothly and progressively, and right now when asked! What corrosion they'd get after a few days out of doors would disappear with a gentle tug of the brake lever, but of course, it was in a mostly low humidity, desert climate, and as such, worked beautifully. The bike had Brembo pads and didn't dust terribly. I can't imagine here in the Pacific North West US, UK and parts of Europe in winter, how they'd be.

Those look the biz! There's nothing like 'better' brakes on a modded motorbike.