Hydraulic brakes always on ( shorted )

[Stephan Linn]

I am fixing a clients bike and BOTH hydraulic brake levers are electrically broken. That is, both brakes work fine as brakes, but the electrical shutoff part is always shorted - independent of lever position. Any ideas what happened and how to fix. Manufactured says to replace. Bike is a Engwe Pro and the brakes are made by Logan.

 

[amberwolf]

To know what happened, we'd need to know the circumstances from when / before the failure started; you'd have to get taht ifno from the rider. Anything else we provide is a guess based on insufficient information.

Do the levers fully retract when let go? (manually moving them back to the stops doesn't change the output)

If the switches themselves are stuck on, even when disconnected from the system, there could be a mechanical malfunction inside the switch, or too high a base pressure in the system keeping them triggered (since they're supposed to trigger with just barely enough lever usage to engage them but not the brakes themselves).

If they aren't stuck on when disconnected from the system, but the system still reads both of them engaged, there's a problem with the system-side connectors, wiring, or electronics.

Some ebrake levers use simple mechanical switches that are either open or shorted, no power required to test / operate. These are easy to test with a multimeter.

Some use hall sensors or other electronic switches that require power (usually 5v), ground, and a pullup resistor from the signal to the + power supply voltage (all of which are in the controller, normally). These can't be tested just with a multimeter, as they require all of those to operate, so you have to build a tester for them that supplies these things if you want to test them independently of the system.



Also, I moved your thread from Bike Mechanical & Structural to Ebike troubleshooting, since this thread is not about mechanical or structural discussions but is about troubleshooting and fixing a problem.

 

[Stephan Linn]

To know what happened, we'd need to know the circumstances from when / before the failure started; you'd have to get taht ifno from the rider. Anything else we provide is a guess based on insufficient information.
----->My customers are not always truthful or accurate when reporting.

Do the levers fully retract when let go? (manually moving them back to the stops doesn't change the output)
----->Yes, levers retract and no change to the output. These are simple 2-wire brakes.

If the switches themselves are stuck on, even when disconnected from the system, there could be a mechanical malfunction inside the switch, or too high a base pressure in the system keeping them triggered (since they're supposed to trigger with just barely enough lever usage to engage them but not the brakes themselves).
-----> I'm thinking high pressure might be the case because the brakes are very hard and the levers are fully retracted.

If they aren't stuck on when disconnected from the system, but the system still reads both of them engaged, there's a problem with the system-side connectors, wiring, or electronics.
-----> The levers are tested unplugged, and show a continuous short. Bike runs fine without brakes connected.

Some ebrake levers use simple mechanical switches that are either open or shorted, no power required to test / operate. These are easy to test with a multimeter.
-----> I'm thinking now that the magnet that actives the sensor never gets close enough.

Thanks for moving the post.
XoXoXo

 

[amberwolf]

To know what happened, we'd need to know the circumstances from when / before the failure started; you'd have to get taht ifno from the rider. Anything else we provide is a guess based on insufficient information.
----->My customers are not always truthful or accurate when reporting.

But...everybody always tells the complete truth about their problems and circumstances, never leaving anything out and never lying! :lol:

Yeah, I know...it's very common here for people asking for help to be that way, which doesn't help us help them; same thing back when I fixed computers for a living, etc. :/

Do the levers fully retract when let go? (manually moving them back to the stops doesn't change the output)
----->Yes, levers retract and no change to the output. These are simple 2-wire brakes.

If the switches themselves are stuck on, even when disconnected from the system, there could be a mechanical malfunction inside the switch, or too high a base pressure in the system keeping them triggered (since they're supposed to trigger with just barely enough lever usage to engage them but not the brakes themselves).
-----> I'm thinking high pressure might be the case because the brakes are very hard and the levers are fully retracted.

If they aren't stuck on when disconnected from the system, but the system still reads both of them engaged, there's a problem with the system-side connectors, wiring, or electronics.
-----> The levers are tested unplugged, and show a continuous short. Bike runs fine without brakes connected.

Some ebrake levers use simple mechanical switches that are either open or shorted, no power required to test / operate. These are easy to test with a multimeter.
-----> I'm thinking now that the magnet that actives the sensor never gets close enough.

Is it a magnet with reed switch, or a mechanical switch?

If it's a reed, sometimes these stick on, and occasionally, tapping the actual reed will unstick them...but more often they're just stuck and have to be replaced. I don't remember any I've seen stuck open.

Most reeds are made so they are open until the magnet is close enough, and close when it is within a certain distance. There *are* NC reeds as well, but they're less common.

Most of the mechanical switches used are NC, so as long as the button is held in by the lever being unpulled, the switch is open--when the lever is pulled far enough (not very far, a few mm at most) the switch button pops up and it closes. Their failure mode is usually stuck closed, depending on their actual internal mechanism, but certain types will stick open and fail to close.


If it's a pressure-activated switch, it is probably not a reed type, and the switch itself is probably not bad, but more likely there's just too much pressure in the system. Bleeding the brakes a teensy bit would probably fix that problem. It's not very likely that it's pressure-activated, simply because that's a more complicated and expensive type of switch, and because it does have the potential to do this.


There may be a removable cover over the switch area; some have this for servicing. If so, it may help you find out what switch is in there, if the manufacturer of the brake system doesn't specify on their pages or the service/user manual for the system.

A google for images of "Logan" brake levers finds some like this that appear to have such covers, but I don't know if they ae for the switch or the reservoir or if these are cable-type, since they just came from the google image search page directly.

 

[Stephan Linn]

OK here it is in all its glory, and I still dont know how it works, and can't find anything like the cable/switch online.

 

[Chalo]

I am fixing a clients bike and BOTH hydraulic brake levers are electrically broken. That is, both brakes work fine as brakes, but the electrical shutoff part is always shorted - independent of lever position.

Why does you client want an inconvenience feature that is doing the problematic thing that all such levers risk doing? Is he or she too incompetent to avoid braking and applying power at the same time?

If so, how does he or she manage to operate other motorized vehicles?

How I deal with switched brake levers, working or not, is to remove the switches and throw them away.

 

[Stephan Linn]

I told the guy it worked fine without. Unfortunately, in Florida the law states that LEVs must have a brake activated shut-off. Not informing the client would make me liable to a law suit.

 

[Chalo]

Unfortunately, in Florida the law states that LEVs must have a brake activated shut-off.

I wish they required annoying BS like that for cars and trucks, not bikes.

 

[amberwolf]

Seems pretty certain that's not a pressure-activated switch, and is pretty likley a magnetically-activated switch, but can't see enough of the lever housing to be certain there's no mechanical external activator.

What's the word on the tube, molded into the casing? There's just enough of it to tell it's a word, but not enough to be sure what it is. Knowing that word might lead to a source for it, or at least more info about it to come up with a replacement.

Does Logan carry spare parts?


The rust on the end implies there's steel or other iron-based metal either as an endcap, an adjuster screw, or...something. Being corroded might not have anything to do with the failure, but it may also be the reason for it.

Is there a magnet in the lever itself? For instance, the round portion that would rotate into the pocket of the lever housing, just inboard of the lever hinge pin? If there is, that would make it certain that it's a magnetic switch, and if it's activated by moving the lever toward the switch, it also tells you it's a Normally Open (NO) type, vs NC (normally closed), since you already know the system works without them connected, and they stuck on (shorted) right now.


The good news is that if you have to, and the client approves, you can use a number of alternative switches, some DIY, to do the same job, if you can't find the original.

Since the magnet is already present, then you can find security-system door or window / etc switches that could be mounted to the levers (probably not exactly where that one is); just has to be NO type. One of the many kinds out there might even be close enough to the original fit right in.

If there is any part of the caliper that moves externally (might not be on hydraulics), you can mount a microswitch (preferably waterproof and saltproof given the climate there) at the caliper itself, using the NC contact (some have both NC and NO and a Common between them), so the roller or lever on the microswitch is held open (by keeping it's lever/roller pushed against it's housing) by the caliper in it's unpulled position, and when you pull the caliper even a little bit it closes the switch contacts. Somewhere around here there's some pictures of someone having made a little bracket to screw to the caliper mount to also hold the microswitch (I used silicone glue as a test measure and it's still working ok on my cable-operated caliper after a few years, but not very clean or neat).