A big issue was encountered with the front brake, specifically the master cylinder, which was totally seized and corroded beyond repair. Bear in mind these pictures were taken after cleaning parts as much as possible to understand the true condition of the master cylinder.
Those who look at these photos and think "that'll clean right up" clearly aren't seeing what I'm seeing. This thing is toast.
Back in the day, BMW made a big fuss about the fact they had located the master cylinder underneath the tank. They claimed this kept it away from harm (true, granted) and that it kept weight and mass more centralized and away from the handlebar (again, true). However, this was an overcomplicated design, requiring a standard Bowden cable from the control lever down to the master cylinder, which was held to the frame with a single jubilee clip, not exactly the most solid arrangement. It also made maintenance much more cumbersome, as the tank had to be removed to even just check the fluid level (although there was an - you guessed it - overcomplicated system whereby a float in the reservoir would lower as fluid level dropped, and this would activate an electrical switch that lit up a warning light on the instrument cluster), or adjust the actuating cable length (which required a special feeler gauge, nowadays no longer available). We started looking for a replacement part, and discovered that these are not only very hard to find, but they are horrendously expensive too. In the end it was simpler and much more economical to switch to a post-'85 13mm handlebar mounted master cylinder, which is exactly what BMW did anyway after the last of the 'slash' series.
These are the parts we needed in order to upgrade the master cylinder (plus a couple of springs and brake pads that aren't strictly needed for this conversion):
32 72 2 310 746 is the handlebar-mounted master cylinder assembly, complete with brake lever; made by Magura and controversially still stamped "made in w-Germany" (as are the handlebar grips);
34 32 1 241 567 is a splitter (also called "distributor") that sits under the tank and is held to the frame with the same jubilee clip (BMW jubilee clips are something else, look at the photo below for detail) that retains the original master cylinder. I'd like something sturdier than that single clip, although in this case it's not as bad as with the original set-up: there you had a Bowden cable pulling on an actuating lever at the master cylinder, so if this wasn't solidly mounted to the frame, it would cause decreased efficiency in the braking force. Here there are no moving parts, this is just a splitter, so it doesn't matter as much if it moves around a bit (which probably won't happen anyway, as there's nothing pulling on it);
34 32 1 242 205 is the banjo bolt (this particular one came with two crush-gaskets, see below);
07 11 9 963 072 (TWO are needed) are the crush-gaskets for the banjo bolt;
32 72 1 457 038 is the twin pull cam gear and chain assembly for the throttle. This is another overly complicated arrangement;
32 72 1 454 129 be the throttle twist grip with pinion gear;
61 31 1 244 334 is the brake switch, made in Italy. It screws into the splitter;
34 32 1 241 565 is the brake hose from the handlebar to the splitter, to suit our touring handlebar;
34 32 1 234 699 (x2) are the brake hoses from the splitter to the fork sliders, where they attach to the rigid lines (also shown below, these are the original ones found on the bike; luckily they survived and were cleaned and re-painted).
The new master cylinder (as assembled within the right-hand handlebar unit, lever, etc.) comprises the cam gear and chain in a housing at the top, secured with a cap, much as with the original, which you can see below:
Our right-hand switch cluster is a nice, direct fit onto the new master cylinder unit:
Those more eagle-eyed among you will notice that the handlebar is back on the motorcycle; this was decently re-chromed and appears to be fairly straight. It's also somewhat unusual for a BMW in that it is a rather tall and wide handlebar, whereas most roadsters to come out of the Spandau factory had a low and very narrow handlebar; the idea was to keep the rider tucked in and leaning slightly forward, in what was considered to be an optimal riding position for aerodynamics and control. To be honest I've never found this to suit me, and I always felt slightly precarious when riding anything (even my own Norton) with narrow handlebars or clip ons. I think it's to do with my upbringing on BMX and mountain bikes, then Honda "enduro" motorcycles. So, this particular unit should feel much nicer to ride.
Considering the complete front brake system, we can't ignore the calipers. They were taken apart and cleaned, then rebuilt using many new parts, such as the pistons. Here you can see a comparison between the old and new parts:
A good cup of tea is never far away when working on these things. Now check this out:
Some of my friends criticized the weight difference as a sign of lesser quality; "they don't build them like they used to!" and "where's the metal?". I like to think it's just a modern improvement that translates to about 250 fewer grams to lug around when braking into a corner, for example.
34 11 2 301 358 (x2) are the brake pads. One set is for one caliper.
34 11 1 231 468 (x2 for the twin disc setup) are springs that press against the eccentric adjusters for the brake calipers, to retain adjustment.
Putting the ATE calipers back together was interesting and relatively straightforward, only one of the dust seals and one of the brake pads fought me a little bit, but all was well in the end; here you can see the new (lighter!) piston pressed in, with the dust seal. There is also a new piston seal housed within the caliper:
They are retained onto the fork sliders by means of a pivot pin, which provides the eccentric adjustment feature.
And with the wheel back on:
The wheel received new bearings and a new spacer. It's a tight fit and everything seems a bit stiff right now, I guess we'll just have to revisit this after a good few break-in miles, considering everything is new up here.
Incidentally, the front wheel is the reinforced type that was probably provided as part of the factory safety recall I had mentioned in a previous post. You should be able to see the extra webbing from the hub to the first crossover "spokes", and this is confirmed by the manufacture date, which is found in the casting:
May 1985, just in time for my sixth birthday.
Another view, angled down towards the hub; notice the extra webbing to reinforce the wheel.
Below is a view of the brake line splitter fitted onto the frame, the electrical terminals for the stop light still need to be connected obviously:
And the banjo bolt at the handlebar:
Fresh DOT4 brake fluid was procured, the reservoir filled and the system primed using our Mityvac. There seems to be some play at the calipers that shouldn't be there, but action at the handlebar lever seems within the norm, though obviously all of this will take a proper test ride to confirm everything is working properly, and most likely additional adjustment (or "dialing in" if you prefer).
