Brake pivot sanity check, '75 XS650B

[scott s]

When attempting to adapt the Pentagram wheels, I had the brake pivot (the splined arm that the foot pedal goes on) completely loose.
I'm having a tough time getting the rear brake switch adjusted correctly and now I'm wondering if I have something installed just a couple of degrees off.

Can you guys check my work?

The brakes work fine. Absolutely no problems, great pedal feel, good travel, excellent stopping, etc. The issue is with the brake switch. It's screwed all the way in and, even then, there's some "pre-load" on the switch. The spring is already pulling out the switch, making adjusting the rear brake light very touchy with a very narrow window of operation. Plus, there's no room for future adjustment.
I replaced the stock switch, tried swapping springs, tried cutting and stretching the spring, etc.


The mark on the splined actuator and the foot lever are lined up and pointing to 12 o'clock.

I never took the arm off the backing plate. This is just how it was when I got the bike. I'm also showing how much threaded rod I have back there.




Now, it's hard to get pictures here, as the arm on the splined actuator shaft is pretty much hidden behind the frame. I'm wondering if it's too far "forward" by a few degrees? Can you see how close it is to the swing arm pivot area?




Would it help if I undid the adjuster at the backing plate, removed the foot pedal, and rotated the actuator to the rear of the bike? Just a spline or two? The only problem I see with that is then the two marks on the shaft and the foot lever would no longer align.

 

[Brassneck]

I think I'd find a longer spring as my first course of action...is the new switch that much shorter than stock?

If I recall (And I can't remember all that's involved), but re-indexing the brake pedal shaft means that the pivot arm that pulls the brake lever, etc. will also move to some degree...not sure if that is a major issue or not though.

 

[Brassneck]

Or a thinner spring with more give so as to relieve some of the tension? My spring is much thinner than the one you show on your bike. Perhaps that's the issue?

 

[scott s]

Would Pep Boys, AutoZone, etc, have replacement springs I could try?

 

[Brassneck]

Would Pep Boys, AutoZone, etc, have replacement springs I could try?

I'm sure they do, or any hardware store. I'd just take the spring with you and get something that same length in different sizes to see what works. Ultimately, you want a spring that has some give so as to not pull the switch until you press the lever.

 

[scott s]

That's a replacement switch but the stock one did the same thing. I think I may have gotten it by stretching the spring I have. I'll ride a bit and report back.

 

[TwoManyXS1Bs]

The rear brake lever (on the brake cam, on the backing plate) is angled too far forward.
Are your brake shoes worn down thin?

 

[scott s]

No....shoes are good. I installed new EBC shoes but I never messed with the cam or lever. That's the position it was in when I got the bike.
Would moving it help with my light switch issue?

 

[scott s]

Here's a picture that better shows the angle of the arm on the backing plate.

 

[Brassneck]

I don't think moving it will help your switch, as the brake pedal/switch are independent to the angle of the brake drum pivot arm.

 

[scott s]

But I should move it a spline or two to the rear?

 

[TwoManyXS1Bs]

Have a look at this member's pic of the rear brake cam/lever arm. With the linkage disconnected, the cam/lever should be pointing nearly straight down.

With worn shoes (or cheap aftermarket thin shoes), the cam/lever will swing forward quite a ways. Properly set up, the brake petal pivot thing will have no choice but to swing rearward so that the linkage will reach the cam/lever arm...

 

[grizld1]

Scott, this ain't rocket science. Take a look at the angle of the spring and brake light switch; it's not a straight pull. Take the spring off and turn it around so that it hooks into the inside of the pivot. That should give you enough slack, but if not, bend the switch mount forward a bit. And as TwoMany says, move that brake arm forward. Choose the position that puts the arm closest to forming a 90* angle with the rod when the brake is adjusted.

 

[scott s]

Rerouted the spring....



....and the brake arm...

Everything seems to be working properly now. I didn't gain a whole lot on the switch, but I did gain some. And it's working great.
Thanks for the sanity check, guys.