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Unread 11-29-2011, 10:38 AM   #1
Spuznick242
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1995 YJ Wrangler 
 
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Shift light?

I've been trying to figure this out on my own but I havent been able to. How does my shift light know not to come on in 5th gear? It does in all of my other gears but 5th and reverse, so that has me thinking its something to do with the reverse switch for the lights or safety switch but I cant figure out how it would do it. Any advice or if anyone knows how it works let me know, I'm not fixing anything, its just something that peaked my intrest.

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Unread 11-29-2011, 10:42 AM   #2
ruthole
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Cuz 5th is your final drive gear and reverse is the only reverse gear why would it need to come on?
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Unread 11-29-2011, 10:43 AM   #3
burnout189
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very interesting question. I have wondered this myself, im curious as to the answers you get.
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Unread 11-29-2011, 10:46 AM   #4
burnout189
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Quote:
Originally Posted by ruthole View Post
Cuz 5th is your final drive gear and reverse is the only reverse gear why would it need to come on?
I think the OP realizes that you cant shift to a gear that isnt there, he is just curious as to how the computer knows that the jeep is in fifth gear. there are no "gear sensors" on the transmission. (other than the back-up light sensor)

its just an interesting question for the guys who like to know how things work.
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Unread 11-29-2011, 11:07 AM   #5
timatoe
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I would think it's based on RPM and you'll likely never hit the same level in reverse or fifth. But that's just a guess, I don't have a shift light.
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Unread 11-29-2011, 11:26 AM   #6
burnout189
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im pretty sure it uses a combination of engine rpm and a vacuum signal from the map sensor to determine when it thinks you should shift. Maybe it also considers the output shaft speed (to speedometer) in determining shift point and current gear?

it doesnt really seem to come on at a particular RPM like a traditional shift light would.

just a guess...
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Unread 11-29-2011, 03:34 PM   #7
Spuznick242
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Thanks guys! I was just bugging myself to death trying to figure it out. My family owns a transmission shop so when my dad asked me, I was like "Uhhhhhhhh, the reverse switch?" but dont worry, you all got credit for your answers.
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Unread 11-29-2011, 03:57 PM   #8
gtrider
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My shift light is comming on in 5th gear since i've re-geared my axles and changed out my speedo gear.
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Unread 11-29-2011, 05:30 PM   #9
alexs93
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I re-geared with 4.11's with 31" tires and I got it in fifth gear before AND after I changed the speedo gear
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Unread 11-29-2011, 05:39 PM   #10
Spuznick242
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I've got 4.11s with 31s too and I dont have it, I've already ran mine out to a whopping 77mph at over 3k rpm and it didnt show up. Then again these are jeeps and everyone of them had a different wiring harness and no two jeeps are even close to being matching.
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