R90/6 stop light switch question

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redavide
Posts: 75
Joined: Tue Dec 04, 2007 12:33 pm

R90/6 stop light switch question

Post by redavide »

I'll be installing one of these shortly. The one that's on the front of the brake master cylinder. Is this just a simple swap or is bleeding brakes, etc. involved? Thanks.

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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am

Re: R90/6 stop light switch question

Post by schrader7032 »

Yes, you'll need to bleed the brakes. The end that pushes into the master cylinder expects to feel brake fluid pressure which is what cause the switch to operate.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

redavide
Posts: 75
Joined: Tue Dec 04, 2007 12:33 pm

Re: R90/6 stop light switch question

Post by redavide »

Thanks . . .

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schrader7032
Posts: 7137
Joined: Fri Oct 27, 2006 3:00 am

Re: R90/6 stop light switch question

Post by schrader7032 »

Brook Reams has a nice pictorial on overhaul the complete master cylinder. At the end, he shows the new pressure switch.

https://brook.reams.me/bmw-motorcycle-r ... k-caliper/

You can test the replacement switch by putting an ohmmeter across the terminals. Then push on the internal switch part to verify that the switch closes. Here's Brook doing that:

https://youtu.be/UV8I1qhjT3U
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

redavide
Posts: 75
Joined: Tue Dec 04, 2007 12:33 pm

Re: R90/6 stop light switch question

Post by redavide »

If I'm only replacing the brake light switch, should I pump out all old brake fluid before removing old switch?

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schrader7032
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Re: R90/6 stop light switch question

Post by schrader7032 »

Might not hurt...should only take a few minutes. But probably not necessary.

When using the brake lever to create pressure and get the fluid to flow out the bleeder, avoid going full-pull on the lever. Since you're not servicing the bore, you could run the inner seals across areas of slight pitting which will tear the seal. You basically want to pull the lever the same amount you do on normal stops...probably about half way. I tape a small thickness of wood onto the grip to limit the travel of the lever. Takes a little longer to push the fluid out, but safer.

Plus you get to pump up your arm muscles more and get ready for the new switch!!
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

MikeL46
Posts: 97
Joined: Fri Jan 01, 2016 1:58 pm

Re: R90/6 stop light switch question

Post by MikeL46 »

I disconnected my front brake light switch. Want to be able to slow quickly w/o brake lights. Of course, sometimes I go a little fast.

Mike
67 R50/2 w/R100 engine/trans and Ural Sidecar
69 R60/2 76 R90S 78 R100RS
70 Triumph w/Spirit Eagle Sidecar

redavide
Posts: 75
Joined: Tue Dec 04, 2007 12:33 pm

Re: R90/6 stop light switch question

Post by redavide »

I also disconnected the front brake switch since when it's connected the brake light stays on all the time which seems a little dangerous when coming to a stop . . . . With the switch disconnected, the brake light turns off and at least the rear brake lever activates the brake light. So, until I install the new switch, I always use the back brakes when I use the front brakes (which is sort of normal anyway) so cars behind me can see I'm braking . . . . .

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