1975 R90/6 front brake switch replacement

[Thomaspin]

First posting here.

My 1975 R90/6, now in my 28th year as second owner, needs the front brake switch replaced. Other than that the bike runs as sweet as a nut, just as it has all these years. It is ridden often.

I have confirmed that the switch remains open circuit when pressure is applied. I have the OEM replacement part and have confirmed that it goes closed circuit when pressure is applied - I used a small rod to test.

My question is: How do I remove the old switch. There is no obvious place for a counterhold to prevent damage as I try to remove the old switch with a 22mm wrench, and I am reluctant to use penetrating oil for fear of compromising the brake fluid. The old one seems to be pretty tight and I am trying to avoid having to remove the whole master cylinder/reservoir assembly.

Thank you for any help you can offer.

[Kurt in S.A.]

Aren't you going to have to bleed the brakes after the switch change? Seems to me that a little penetrant, and it would be small, will be flushed out at that point.

What about holding the master cylinder in place with the existing hose clamp...wouldn't that be enough of a hold to turn the switch off?

Kurt in S.A.

[jagarra]

You could grab the body of the MC with a pair a slip joint or water pump pliers to keep it from rotating. You probably won't lose enough fluid to require bleeding the systems as the flow will be outward no air coming in.

[Wobbly]

My question is: How do I remove the old switch. The old one seems to be pretty tight and I am trying to avoid having to remove the whole master cylinder/reservoir assembly.

Loosen the m/c band clamp, slide the m/c slightly rearward, re-tighten the clamp. The switch is fitted with a tapered thread to keep it from leaking, so of course it seems tight. Unscrew the old switch and then install the new switch. Tighten only enough to keep it from leaking.

Put the m/c back where it was originally.