1977 R100RS - brake and electrical questions

[6bikegarage]

Hello,
I am helping a friend get her '77 R100RS running and rideable so she can sell it and I have run into a couple issues. First off are the brakes. The brake fluid was pretty grim so I pulled the calipers and took them apart (a link to a video about the bike is below). I expected to find the pistons rusted, but they looked much better than I expected (except the recesses on the side that presses into the back of the pads). I ordered new seals, pads, o-rings and and pressure switch (that was dead too) and started reassembly. When it came time to slide the pistons into the caliper, they didn't want to go in. I lubricated both the new oil seal and the walls of the piston with brake fluid, but it was way harder to press them in than I've ever experienced on a brake rebuild. Now that I'm at a point where I'm trying to bleed them (still working to build pressure, but had to take a break), they grab the disc, but don't fully release. When you let go of the lever, the wheel will turn with force, but mot easily. Is this normal? Am I missing something?

As mentioned, I had to take a brake from trying to fully build pressure (hoping there isn't a master cylinder rebuild in my future). While taking the break, I figured there was enough pressure that I could confirm the brake light switch is at least working and that the brake light would now come on. When I turned the key, I found the battery was completely dead. It is only a few weeks old and shouldn't be unless there is something drawing on it.

It was so low that at first I couldn't even get the battery tender to charge it (just gave the flashing red "not charging" light). I gave it a bit of a boost from a jump pack and tried the battery tender again. Now it was at 4v and giving a solid red light indicating it was charging. After a bit of puttering with other things, I heard a re-occurring clicking sound. It sounded like a relay and I confirmed it would stop if I disconnected the battery negative. I traced it to the horn relay that sits to the left of the master cylinder by the frame. Previously (in the video below), the horn wasn't working until had pushed on that relay a bit. I think the reason it is clicking is that the voltage is so low it can't hold the relay contact closed and it keeps falling back to open and I didn't hear the clicking before because the battery had enough power to just hold the relay closed. Now I need to figure out why there is power at the relay when the key is out of the ignition. I'm sitting down with a wiring diagram to try and figure it out, but if anyone has any ideas or think they can point me in the right direction, I'd love to hear them.

https://youtu.be/4Y9jugE1g-o?si=UNZRxbcJeZd-akFZ

Many thanks,
jason in Seattle / 6 Bike Garage

[6bikegarage]

after studying the wiring diagram I'm, if anything, more confused. If I understand the relay operation, when you press the horn button on the switch gear, it completes the coil circuit in the relay, which closes the gate and allows battery power to flow to the horn. Power can't get to the horn button unless the ignition switch is on. If the clicking I heard was the the relay activating, what was triggering it. The ignition was off. if somehow, there was a short allowing power to the button, the button doesn't seem stuck and if it was, wouldn't that keep the continuity from the battery to the horn and the horn sounding?

Also, wanted to ask one other thing about the brakes. The pads closest to the wheel (opposite the caliper piston) have a paper clip like wire retainer. This doesn't feel very secure. It has a pretty good bow to it and it feels like it could slip off the notch on the brake pad post. It's holding right now, but it doesn't seem right. Am I missing something there too?

Thanks for any help.

Cheers

[Rob Frankham]

It sounds to me like there is something basic wrong electrically. It also sounds very much like the battery has been run completely flat and there is a good chance that it has been damaged. Try charging it fully (off the bike) and see if it will hold a charge.

You need to go through the wiring... do you have any idea what the condition of the bike when it was parked up... that might give some clues. One thing is for sure. There is no way the horn relay will be actuating with the ignition off unless there is something wrong with the way things are connected up. This may also explain why the battery has been flattened

Unless you are willing ( and dare I say, competent) to go through through the wiring systematically and sort it out from basics, I think you may have to use an auto electrician.

The brake also doesn't sound good. The piston should be fairly free in the caliper when there is no fluid in the system. If the system is full, there will be some resistance but it should retract enough for the wheel to spin freely (with perhaps just a very slight sound of contact). It certainly shouldn't require any great force to turn the wheel...

Sorry if that's not much help. It's difficult to make any realistic diagnoistic without a lot more information or access to the machine.

At the end of the day, it may be better to advise your friend to sell the bike as a non-runner than to enter into a possibly protracted and expensive series of repairs.

Rob

[6bikegarage]

thanks for response. I've been studying things and I think the relay may be the issue. Power is supposed to go through the ignition to the button. When the button is pressed, it allows the power to flow through the relay to ground. This energizes the coil creating a small electromagnet that closes the "gate" an allows power to flow straight from the battery to the horn and ground. I think that the "gate" was sticky and not falling back to it's full open position. Sitting in close proximity to the contact could allow the power to build and arc across the gap (the regular clicking I was hearing was more of a zap). I ran this theory by a friend with way more electrical knowledge than I have and he agreed that it is likely what is happening. I'm charging the battery and will see if it holds a charge and then I'm going to replace the relay and watch for any voltage drop.

the brakes are a weird one. They are the same pistons and calipers that were with the bike. Its almost like the oil seals are wrong, but I got them from a reputable BMW parts site and they visually fit the caliper bodies perfectly. I might have to drain fluid and break them down again. Hmmm.