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post #1 of 36 Old 11-04-2015, 09:50 PM Thread Starter
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jeep won't trigger stop lights

i've noticed that my jeep (2013 JKU with a 2.5 lift and 35" tires) has trouble triggering stop lights. there are some lights that simply will not trigger unless another vehicle pulls up behind me. i've tried pulling up far to the point where i am almost in the crosswalk. i've tried staying back. i've tried far left, far right and dead center of the lane. i've tried rolling back and forth in the area where the motion sensors were installed into the pavement. my wife's minivan will trigger these same lights instantly, before she even comes to a complete stop. whereas i have had to resort to getting out of the jeep and pushing the walk button to get the light to turn.

there is even one intersection by my house that, when i pull up, the cross traffic will get a yellow light, then a red light, then immediately turn green again without my light ever turning green! again, this light always works fine with my wife's minivan.

i assume this has something to do with the bulk of the jeep being higher off the ground than the average vehicle, combined with a sensor that isn't very sensitive. anyone else have this problem and any tips to get the lights to trigger short of running out and hitting the walk button?
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post #2 of 36 Old 11-04-2015, 10:01 PM
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I get this a lot of the time too. I'd also be interested in knowing the legality of safely running the red light. As in no one is remotely near me when doing so.

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post #3 of 36 Old 11-04-2015, 10:31 PM
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My Jeep is pretty low over its 35s with a big-ass steel skid underneath, but on rare occasions I also have that happen.
My theory is: if I've sat through at least 1 or 2 cycles of the light, and I run it safely, no reasonable cop would balk at my 'splainin'.

BUT WAIT - YOU CAN FIX IT! :
Some folks install a large-ish neodymium magnet on the bottom of their front diff (or bicycle, scooter, motorcycle, etc.) to trigger the inductive loop sensors.

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post #4 of 36 Old 11-05-2015, 05:24 AM
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Quote:
Originally Posted by ExWrench View Post
My Jeep is pretty low over its 35s with a big-ass steel skid underneath, but on rare occasions I also have that happen.
My theory is: if I've sat through at least 1 or 2 cycles of the light, and I run it safely, no reasonable cop would balk at my 'splainin'.

BUT WAIT - YOU CAN FIX IT! :
Some folks install a large-ish neodymium magnet on the bottom of their front diff (or bicycle, scooter, motorcycle, etc.) to trigger the inductive loop sensors.

^ This - Neodymium magnet - doesn't not even need to be a big one and they sell them specifically for this reason.

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post #5 of 36 Old 11-05-2015, 05:26 AM
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Most states have a law that states that if a signal is not working or malfunctioning, you are required to treat it as a four-way stop. If the sensor is not working, that's a malfunction. Stop and go. YMMV. IANAL, and all that....

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post #6 of 36 Old 11-05-2015, 05:50 AM
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Actually the sensors are triggered by weight
So you need to add weight. The easiest thing
To fix this is for you to gain just little
More weight and the best way to do that
Is to quit pooping so no poppie for boopie.

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post #7 of 36 Old 11-05-2015, 07:42 AM
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Magnet.

Use this trick on my motorcycle as it has the same problem. I have heard of laws specifically for bikes where you can legally run the light after a 5 min wait. (varies by state), but I've never heard of it applying to vehicles.

If you are a cheapskate and have an old hard drive laying around, you can open it up and you should find a neodymium magnet inside. Usually small and banana shaped. Works for the bike.

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post #8 of 36 Old 11-05-2015, 07:48 AM
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Quote:
Originally Posted by RubiCajun View Post
Actually the sensors are triggered by weight
So you need to add weight. The easiest thing
To fix this is for you to gain just little
More weight and the best way to do that
Is to quit pooping so no poppie for boopie.
Not true.... how does my 25 pound road bike trigger the lights ?

the neodyne magnets are a huge thing in the cycling community

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post #9 of 36 Old 11-05-2015, 07:56 AM
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Originally Posted by FuLcRuM View Post
Magnet.

Use this trick on my motorcycle as it has the same problem. I have heard of laws specifically for bikes where you can legally run the light after a 5 min wait. (varies by state), but I've never heard of it applying to vehicles.

If you are a cheapskate and have an old hard drive laying around, you can open it up and you should find a neodymium magnet inside. Usually small and banana shaped. Works for the bike.
^^This.

The vast majority of stoplights now use inductive loops in the pavement to detect the presence of something metallic inside the loop.

Motorcycles often don't contain enough metal for the inductive loop to detect accurately, so many will add neodymium magnets. Oklahoma has enacted a law to allow (only) motorcycles to proceed through a red light if they have stopped and the light hasn't changed because, well, it doesn't know they're there.

With your Jeep being lifted, it's likely you don't have enough metal close enough to the pavement for the inductive loop to detect its presence.

Sticking a magnet to your front diff should solve the problem.

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post #10 of 36 Old 11-05-2015, 09:26 AM
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Some sensors are weight, others are inductive loop...

Lifted jeeps just need either an air ride suspension or some sort of go-go-gadget bellypan to trigger the magnetic sensor...

I think the "light didn't work" argument will fail as soon as they prove it was your vehicle mods that caused the anomaly, not a defect in their equipment.

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post #11 of 36 Old 11-05-2015, 09:30 AM
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I believe its triggered by metal. We might be a little to high to catch the sensors. If you look on the street you can sometimes see the outlines in the asphalt were the sensors are.
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post #12 of 36 Old 11-05-2015, 11:28 AM
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Quote:
Originally Posted by Asmmns View Post
Not true.... how does my 25 pound road bike trigger the lights ?

the neodyne magnets are a huge thing in the cycling community
Shame on you. You of all people should know not to take me seriously.....all the time. I have no clue as to what activates the lights.

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post #13 of 36 Old 11-05-2015, 11:35 AM
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Quote:
Originally Posted by RubiCajun View Post
Shame on you. You of all people should know not to take me seriously.....all the time. I have no clue as to what activates the lights.
I actually thought that after I typed it.... but was multitasking. Damn I'm usually pretty sharp on those !

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post #14 of 36 Old 11-05-2015, 11:50 AM
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I have a light that I hit every morning on my way home from work. I have pull up stop put it in reverse back up and repeat a few times. It is a busy bad ass intersection and unfortunately I am the only one ever headed in my direction at 0600 hours. Not safe to run it either as cross traffic is heavy going 5mph and 5 lanes of traffic. Usually a couple back and forths trigger it.
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post #15 of 36 Old 11-05-2015, 12:05 PM
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Quote:
Originally Posted by ExWrench View Post
BUT WAIT - YOU CAN FIX IT! :
Some folks install a large-ish neodymium magnet on the bottom of their front diff (or bicycle, scooter, motorcycle, etc.) to trigger the inductive loop sensors.
Thanks for this, Ex. There is this one diabolical light by my house that gets me all of the time. Sometimes I have even hopped out and hit the pedestrian crossing button.
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post #16 of 36 Old 11-05-2015, 12:26 PM Thread Starter
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how large of a neo magnet would i need? my kids and i race slot cars. they usually come with magnets but we race without magnets so i have a buttload of tiny magnets (like 8mm wide, 3mm tall wafers). would sticking 10 of these on my diff work, or do i need one big magnet?
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post #17 of 36 Old 11-05-2015, 01:48 PM
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Jumping out to push the button or adding some magnet seems like a lot of work. I would just run the stop light.

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post #18 of 36 Old 11-05-2015, 02:14 PM
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So I had this old (ESDI?) hard drive laying around out of an old Octel voice mail system and it just happened to have the most perfect magnets!

There were two inside and they did not even need to be glued in. I just tapped them out with a long punch and hammer.

They are perfectly shaped to fit right to the axle tube in a protected spot above the LCAs.

If just one works for me, you can come by and grab the other.






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post #19 of 36 Old 11-06-2015, 03:56 AM
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Looks like it may be legal to run the stop light in some states.

If this article that I found on a Vespa board is correct, then here in California we can just call the city and ask them to fix it.

The article is also suggesting that magnets do not work either because the loops do not actually detect a magnetic field - they detect metal.

So far my magnet test has been unsuccessful, which would corroborate the above.

http://modernvespa.com/forum/wiki-trafficsignals

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post #20 of 36 Old 11-06-2015, 07:14 AM
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Quote:
Originally Posted by White13JKUR View Post
Looks like it may be legal to run the stop light in some states.

If this article that I found on a Vespa board is correct, then here in California we can just call the city and ask them to fix it.

The article is also suggesting that magnets do not work either because the loops do not actually detect a magnetic field - they detect metal.

So far my magnet test has been unsuccessful, which would corroborate the above.

http://modernvespa.com/forum/wiki-trafficsignals
But like mentioned before it only applies to 2 wheeled vehicles for running the light.

The theory I was told is the magnet disrupts the magnetic field of the sensor which is exactly what a large chunk of metal does.

It seems to work for me, but I don't ride much in the city anymore either.

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post #21 of 36 Old 11-06-2015, 09:02 AM
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Quote:
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The theory I was told is the magnet disrupts the magnetic field of the sensor which is exactly what a large chunk of metal does.

It seems to work for me, but I don't ride much in the city anymore either.
I have not had enough time with the magnet to really say one way or the other but it did not seem to have an effect on the one light over here that has been giving me sand in the private parts.

FWIW, the magnet supposedly works not because it is magnetic but because it is a large metal object.

That said, I will still try a few different locations to see if the magnet trick works on a jeep. That and I will try to be more conscious of where the axle housings are in relation to the loop wire. Might be best to line up a front or rear axle housing directly over the loop wire since that is the lowest metal on the jeep.
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post #22 of 36 Old 11-06-2015, 10:13 AM Thread Starter
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i just spoke with one of my coworkers who rides a motorcycle and he said he has a large puck shaped magnet on his bike and does help trigger stop lights. but he also has it in a position that is significantly lower than a jeep axle. after researching it a bit, some riders even put the magnet on their boot so that they can put their foot down right on the sensor.

as the distance increases, magnetic forces decrease exponentially. so a magnet on an axle that is 12 inches above the road will have significantly less effect than a magnet on a motorcycle cowl 6 inches above the road. i don't know the formula, but it definitely isn't half as strong when it is twice as far... it's probably more like 1/10 as strong or maybe even less...

best bet might be to position the magnet at the lowest point on the diff, and don't forget to remove it when you're offroad...

last night i put a bunch of slot car magnets inside my LCA skids so they are lower than axle height but protected from rocks and freeway speed wind. but i haven't had a chance to test them on any finicky lights yet. based on what i have learned from this thread, i doubt they are going to work.

Last edited by boopiejones; 11-06-2015 at 10:17 AM.
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post #23 of 36 Old 11-06-2015, 12:23 PM
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I just rev up my engine so that it creates a stronger electromagnetic field. Could be placebo effect though.
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post #24 of 36 Old 11-06-2015, 01:10 PM
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Just hang an iron ball on the end of you winch, spool out when you are pulling up to a light, spool back in when it turns green.

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post #25 of 36 Old 11-06-2015, 02:09 PM
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Quote:
Originally Posted by pepeslav View Post
I just rev up my engine so that it creates a stronger electromagnetic field. Could be placebo effect though.
Placebo. As I have come to learn, these loop sensors detect metal like a metal detector does. They do not detect a magnetic field. They detect magnets because they are metal.

I thought of triggering the lockers (stronger electromagnetic field plus closer to the ground) but abandoned the idea after learning the above. I have a diablosport trinity that I sometimes bring with me so maybe I can use it to flick the lockers on.


Another biker's trick is to just whip out your kick stand and touch it to the loop cut in the pavement. I rode several bikes for many years but never knew that trick until now.
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