Attempting a handlebar master cylinder relocation on 1975 R90S

[hogarthd]

Hey folks -

I'm working on replacing the under-tank MC with the handlebar MC on my 1975 RS. I've read thru Snowbum's article and gotten all the parts needed. I'm confused by one thing, though - Snowbum recommends the hydraulic junction from an R100RS as a place for the three brake lines to converge AND a place for the brake switch to screw into. This doesn't make any sense - the junction has a L/R output that goes to the lines for each brake caliper (dual disc) and a single input connection that will come from the handlebar MC to feed the L/R lines. Looking at the R100RS fiche, though, they show the brake switch screwed into that single port - so how do you get two brake lines coming out of it?

The Max's BMW fiche says "has 4 ports" but the part that Euromotoelectrics carried has only 3 ports?

This is the part I have -

 

[kinterridge]

I used the EME part you show on my '77 R100S works just fine.

 

[hogarthd]

I used the EME part you show on my '77 R100S works just fine.

Awesome - how do you hook up two brake lines, a master cylinder line AND a brake pressure switch (4 ports) to that part?

 

[20774]

The EME part seems to have a fourth hole on the backside. Is this where the brake pressure switch installs?

 

[hogarthd]

My part does not have that 4th hole - it has a little pinhole at the top of it, the L/R holes which are in a Y shape, and then a third, threaded hole for the line running from the MC.

 

[20774]

What EME part number did you order?

 

[stevenrankin]

On bikes with the handle bar mounted master cylinder, the brake switch is in the handle bar unit.

The part you have is only the splitter from one main line in and two out. The tiny hole is threaded and is for mounting the ignition control module unit found on bikes that have electronic ignition.
Who knows why Max's fiche says four ports, they made a mistake. St.

 

[melville]

The 4th port is convenient to have for a brake light switch because the wire for the brake light is right there. That said, there's probably also an unused brake light wire in the headlight bucket. The wiring harness on my /6 has an unused brake light wire in the headlight bucket. BMW left it there presumably for the R60 version with a drum front brake. The drum brake versions used a lever mounted brake light switch.

So if your handlebar mounted MC has a built in brake light switch, just fish the extra wire out of the headlight and run it to the MC. Tape off the wire under the tank. Also tape off the brake failure warning light wires as a general thing.

Otherwise, if your splitter doesn't have a brake light switch port, you can add one. The brake light switch is 1/8" NPT. As it's a tapered thread, don't tap too deeply as you do not want the switch bottoming out.

 

[stevenrankin]

I stand minor corrected. The four port distributor is No longer available from BMW. So it looks like BMW used to carry one but no longer does. It may be that part was used in the cross over period from ATE brakes to Brembo in 80 or 81.

Brows Ebay and see if one turns up. Or see about drilling and tapping or running a pair of wires to the handlebar switch. St.

 

[ccolwell]

There are banjo bolts with integrated brake light switches available.

 

[SGTBILL]

I am working on an R100S that had a master cylinder relocation done as part of an upgrade to later Brembo brakes from ATE brakes. I would only say that it is a pain to get to the MC cap screws without removing the S fairing. And that is a pain. So much pain. Personally, I'd be tempted to put a MC back under that tank at this point. YMMV.

 

[stevenrankin]

When I converted my 78RS to Brembo brakes, I purchased off Ebay all the necessary parts needed to go whole hog. I did the change in stages first changing the forks and calipers. Lo and behold I found that once that was done, I didn't need to move the MC. A bit of fiddling to take a little play out of the cable and the converted bike's brakes worked just as good as the brakes on my 84RT with the handlebars MC. So, now, I am converting a 79RT to Brembos and again, I am going to skip moving the MC.

LOL, I guess my point is the MC is an MC wether it is on the handlebar or under the tank, the only difference being the bake cable actuating the under the tank unit, and if that cable is set right, it don't stretch enough to notice the minor difference between a handle bar unit or the under tank unit.

Then again that is my experience, lots of times over the years I spent time and money in performance improvements only to find I couldn't tell I improve performance, only lightened my wallet. St.