Rear brake won't release?

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fcherny
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Last seen: 7 years 11 months ago
Joined: Wednesday, July 18, 2007 - 10:49
Points: 81
Rear brake won't release?

I rode my z20b to work yesterday for the first time ever (a 10 mile trip) and it worked great! It only consumed about 1/4 or less of my battery charge.

But on the way home, I ran into a problem. In retrospect, I think this has been a problem with the bike for a while (before I got the new controller). The problem, I believe, is that the rear brake is clamping down and not releasing. This happens even when I don't have my hand on the brake.

What happened was: I left work and the bike was riding fine. About half way home, the bike started to slow down. Then it would only go about about 5 - 10 mph. Then not at all. I pulled off to the side of the road. With the ignition on, I found I could not push the bike (as I normally can do). I turned it off and on. The bike would go very slowly for a few feet, then stop. Again, I could not push the bike any distance at all - as if someone were squeezing the brake. I waited, thinking the bike needed to cool down (it was 102 F yesterday). I waited in the shade. But the next test, same result. Finally I threw off the circuit breaker and waited a bit longer. Turned everything on. Even though I could not push the bike very easily, it seemed to be better. I started riding down the road slowly. Eventually, things started working again and I was able to travel full speed. But by the time I got home, almost all my charge was gone. The gauge was blinking red when I pulled into the garage.

I started thinking over the ride home. I remembered that before the bike stopped, the bike had started to act strange. When I was approaching a stop and I took my hand off the throttle, rather than rolling to a stop (like I was used to), the bike was stopping fast, like I had the brake on. And I've seen the brakes lock up before, but I thought it was something wrong that I had done. For example, some time ago, I was backing up out of the garage (sitting on the bike and pushing back with my legs) and noticed it was very hard to move the bike. But I had the ignition off. So I thought it had some connection with that. Again, I turned everything off and turned it all on, and the problem corrected itself.

Can anyone tell me how the brakes work? Can the controller or anything else activate them? What do I need to diagnose and fix the problem? Can someone send me some pictures of how to dismount and inspect the brake pads to make sure everything is working like it should? Can you think of anything else this could be?

Thanks,
Fred
z20b

monroe Eskew
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Last seen: 10 years 2 months ago
Joined: Sunday, January 4, 2009 - 21:36
Points: 16
Re: Rear brake won't release?

Take it to a local motorcycle/scooter shop. It is a standard disc brake, nothing special. They can adjust it or replace it for you.

wookey
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Last seen: 7 years 7 months ago
Joined: Wednesday, April 8, 2009 - 06:12
Points: 90
Re: Rear brake won't release?

More likely a drum brake in fact. I had the same problem with my scooter. It's a common problem with drum-brake scooters in general, especially after winter, when the road salt corrodes the brake shaft where it goes into the hub until the spring is not sufficient to release it. I took mine to bits (not totally obvious how to do it) and greased it and now it's fine. If you don't like to do your own mechanics any motorbike/scooter shop can sort it out for you.

Wookey
Sakura s50 (Efun A)

FrankenstienEV
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Re: Rear brake won't release?

Next time this happens, loosen the bleeder valve on the caliper 1/4 turn and then tighten it right back up quickly. Now try to push the bike without touching the brakes. If it moves easily now you may have a defective master cylinder. When the brake handle is fully released, the brake fluid should be able to flow freely in and out of the resevoir. You should be able to push the brake piston in without too much difficulty. If the master cylinder is maintaining pressure with the brake handle in the fully released position, then any heat like from the motor or from the brakes dragging will heat up the brake fluid causing it to expand and apply pressure to the caliper, making the brakes drag more. The only thing I don't underrstand is how turning the ignition on and off accomplished anything. There really isn't any connection between the two...might have just been a fluke! The Ohm Depot

fcherny
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Last seen: 7 years 11 months ago
Joined: Wednesday, July 18, 2007 - 10:49
Points: 81
Re: Rear brake won't release?

Thanks! That's a good idea. But what's the "bleeder valve"? (See pics in R-20 Rear Brake Issue (brakes fell off) thread).

I think the reason my efforts worked was: more time had elapsed (letting the bike cool) and I had put the bike up on the center stand before shutting off the circuit breaker. After turning the breaker on, I pushed the bike off the kickstand. The jolt might have helped loosen the brakes enough to get me home.

Are there any good resources on the web that would help me understand a bike's brake system?

Thanks again for your help.

FrankenstienEV
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Last seen: 6 years 1 month ago
Joined: Tuesday, March 31, 2009 - 05:41
Points: 22
Re: Rear brake won't release?

Those pictures came in handy in the "brake issues" (brakes fell off) because I don't have my Z-20 with me and I was trying to remember what the caliper looked like!! On the caliper, above where the brake hose attaches you will find a little rubber cap. Pull off the cap and you will see a metal fitting with a hole in the center. This fitting is your bleeder valve. If the system has air in it, you can remove it using this bleeder valve. But in your case, the system might be maintaining pressure. Opening the bleeder will relieve the pressure. Don't squeeze the brake lever when you are doing this or brake fluid will squirt out of the little hole in the bleeder valve and/or you could risk sucking a lot of air into your system if you release the lever with the bleeder valve open. I meant to ask you if the rear brake lever had the normal amount of free play in it when the brake was dragging or was it real tight (zero free play)? If the master cylinder is the problem then the brake lever will have zero play. If you have the normal amount of play when the brake is dragging then you could have a collapsed brake hose. That too will maintain pressure...acting like a one way valve...allowing brake fluid to be pumped to the caliper when you squeeze the brake lever, but not allowing it to return to the master cylinder when you release the lever. I had an old 1957 VW Bug that had a collapsed brake line and as soon as I opened the bleeder valve I could hear those old creeky brake shoes release and the wheel turned freely. I put on a new brake hose and bled the system and it was fine. Good Luck Bro, The Ohm Depot

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