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Old 09-16-2012, 11:33 AM   #1
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Question Jumping Speedometer Driving Me Nuts...Please Help!

Hey everyone,

My speedometer has been jumping for about a month now and it is literally driving me insane. I've contemplated just ripping out the instrument cluster entirely =)

Some background:

2002 TJ with 5 speed manual and stock driveline, 3.07 gears, 27 tooth speedometer pinion gear, 31" tires.

The speedometer started randomly jumping about a month ago. There was no rhyme or reason to it (so I thought). The tach does NOT jump at all and reads proper.

I replaced the VSS as a first step. Nothing changed. I pulled out the pinion gear, inspected and cleaned, reassembled, no change. Tried a NEW pinion gear. No change.

This is when I noticed something funny. With the VSS completely unplugged, the speedometer STILL JUMPS!!! This is definitely not mechanical.

Not only that, but I can "trigger" a jump by doing the following:

With the vehicle idling in neutral and the VSS UNPLUGGED, if I punch the gas (spike the RPM from <1000 to say 4000 very quickly, the speedometer will jump erratically. It is never the "same" jump. Sometimes is might go up slightly to say 30mph, other times is will peg out the gauge. Sometime on its way back down to 0, it will jump back UP a few times before settling down.

So, before you say this is a "grounding issue" - please help me out and guide me where to look, cause I've checked every electrical connector and ground location I can find on this thing and I'm about to give up. Could my CPS need replaced? Could the hall effect of that sensor affect the speedometer? Has anyone seen anything like this before? Is the cluster bad? I would just love to know where to look next - as I'm running out of ideas...and I hate that.

Any info would be appreciated!

Thanks,
Ken

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Old 09-16-2012, 02:44 PM   #2
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I'm not sure this applies to a jeep but when the speedometer uses a cable sometimes the cable needs to be lubed. I had the same problem in my older cars and my TR6. I used to pull the cable out clean it and then put a little grease on it and re-install.

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Old 09-16-2012, 03:19 PM   #3
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yea i stretched out a speedo cable in a mercedes i had and it jumped from doing so, just sprayed it with some lube and worked fine since .
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Old 09-16-2012, 03:36 PM   #4
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That is strange, Jeeps don't have the cable it is all wires.... Have you tired calling dealer and picking a service techs brain??? This is going to take some time trouble shooting....
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Old 09-16-2012, 03:43 PM   #5
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Jeeps don't have speedometer cables, those haven't been used in many years.

Your issue is very likely (99.9999%) the speedometer gear was replaced and whoever replaced it didn't rotate the speedometer gear housing far enough to get the speedometer gear fully meshed with the pinion gear inside. Very likely rotating it a bit more will cure the problem.

Look at this website for clarity on rotating the speedometer housing to the right position... Changing Your Jeep Speedometer Gear
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Old 09-16-2012, 03:56 PM   #6
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Quote:
Originally Posted by Jerry Bransford
Jeeps don't have speedometer cables, those haven't been used in many years.

Your issue is very likely (99.9999%) the speedometer gear was replaced and whoever replaced it didn't rotate the speedometer gear housing far enough to get the speedometer gear fully meshed with the pinion gear inside. Very likely rotating it a bit more will cure the problem.

Look at this website for clarity on rotating the speedometer housing to the right position... Changing Your Jeep Speedometer Gear
X2, exactly what I was thinking. Make sure the correct gear number lines up with the little dot on the transfer case
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Old 09-16-2012, 04:41 PM   #7
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Thanks for all the replies so far...

Please re-read my original post where I note that the VSS is UNPLUGGED and the speedo still jumps. There is no speedometer cable in a TJ, it's all electrical. If I plug in my VSS it still jumps. It doesn't matter if I have a 27 tooth, a 29 tooth, or ANY speedo gear installed, properly or not (and yes the sensor housing is rotated correctly), the speedo still jumps without the VSS plugged in. I am 99% sure this is electrical and not mechanical.

Any takers????

I will try to call a tech tomorrow and see if I get anywhere.

Thanks again!
-Ken
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Old 09-16-2012, 05:03 PM   #8
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Quote:
Originally Posted by ken78744 View Post
That is strange, Jeeps don't have the cable it is all wires.... Have you tired calling dealer and picking a service techs brain??? This is going to take some time trouble shooting....
I haven't had to worked on a speedo in such a long time I didn't if they did away with the cable or not. That's why I said I don't know if it applies.
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Old 09-17-2012, 02:30 AM   #9
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Originally Posted by jeepwayoflife View Post
X2, exactly what I was thinking. Make sure the correct gear number lines up with the little dot on the transfer case
sorry for thread jack but
I have the same trouble with mine, however, my speedo is a sensor and tone ring ( came with Mega Short SYE ) not a gear /spline setup.

I have replaced the sensor once before and the problem went away for a while but now it's back head is getting sore, will be watching with interest.

cheers
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Old 09-17-2012, 07:17 AM   #10
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Quote:
Originally Posted by WRNGLR View Post
sorry for thread jack but
I have the same trouble with mine, however, my speedo is a sensor and tone ring ( came with Mega Short SYE ) not a gear /spline setup.

I have replaced the sensor once before and the problem went away for a while but now it's back
i am having the same issue with mine. i've got the teraflex super short sye that the previous owner installed. i talked with teraflex & they advised that the sensors go bad & sold me a sensor. i replaced it, but still had the same problem. teraflex sent me a new tone ring & nut to secure it. they advised that sometimes the nut holding the tone ring works itself off & then the ring doesn't always spin giving it an erratic reading.

i was going to have a local off road shop install it for me while my TJ was in for some other stuff. but then the guy told me it sounds like it might be the cluster itself. he was saying that if it were the tone ring, since the signal would not be getting to the pcm/cluster, it would set off the check engine light. i'm not sure if that's totally true, but made sense. teraflex did not say anything like that, as he sounded like it doesn't happen all the time, but has happened.

i'd like to know if anyone else has had this issue too, since i did not really want to replace the cluster since the original cluster has the original (low) mileage on the display. the replace cluster has over 240k.
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Old 09-17-2012, 05:57 PM   #11
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I have had the OP's exact problem, and with the help of .458 on this forum, I have a solution for you!

Replace the spark plugs, spark plug wires, and coil (or coil rail).

Here's the best theory as to what happened to both .458 and myself:

1.) Original spark plugs were left in too long (~100k miles)
2.) Spark plug gap became too large
3.) Spark started arcing in the coil as that was path of least resistance
4.) High voltage traveled along the coil source or sink wires back to the PCM
5.) in .458's case, a MOSFET driver chip in the PCM eventually died, preventing the alternator regulator and (nearby) speedometer circuit from working properly
6.) in my case, the high voltage spike occasionally interfered with the charging & speedo systems (but did not destroy the chip)

.458's solution was to replace the plugs, wires, coil rail & desolder/replace the MOSFET driver chip in his PCM.

My solution was to replace the plugs, wires & coil. My PCM was not permanently damaged.

Our charging systems & speedos now work properly.

Good luck!
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Old 09-23-2012, 01:24 PM   #12
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Checking in - did anyone have success with my suggestions?
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Old 09-23-2012, 06:54 PM   #13
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hmm, i guess i could five that a shot for mine. age may be a factor, but not due to mileage (since mine only has 42k on it). but i'm not sure if they have ever been changed. i might give it a shot & see what happens. maintenance never hurt anything, right?
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Old 10-09-2012, 08:12 PM   #14
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I'm haveing the same exact problem and I'm ready to get rid of my jeep because it irritates me so much!! I've changed my vss and calibrated the gauges. I've looked for the timing but couldn't find the little mark around the sensor to time the gear. I've only owned for about 2 months and it's my first jeep so idk much about it. My tires are 35"s. my biggest concern is sometimes when I'm on the highway going about 60ish (speedometer gauge just bounces around) my needle will bounce up over 100mph and then the vehicle jerks me down slower like its got a governo it's hitting. Has anyone actually had success fixing this yet? The coil rails over $100 so I'm hesitant to change that without knowing for sure. Oh and I only have about 60k miles on it if that makes a difference. Please please help!! This problem makes me hate jeeps something I've loved since I was a child!!
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Old 09-20-2013, 05:11 PM   #15
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Did this ever get figured out? I have a YJ, but same TC and speedo setup. Same exact thing has been happening to mine as the OP. I only have 100k on it. Already replaced the speedo sensor. The weird part is that is jumps when reving the engine while parked.
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Old 12-26-2013, 09:05 AM   #16
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Just start happening on mine last week. Its 2003 TJ and have had it since it was born. Just changed the spark plugs a couple months ago. Over the Summer a mega short SYE went in so the speedo is no longer a gear but a sensor. Still using the the same sensor since upgrading to the new mega short.

Going to check that the sensor didn't come loose per recommendation above (hard to believe, but worth a check).

Been having strange electrical things occur this past year where one interior light on the sound bar would light up fine and the other would take a vacation most of the time. I put LEDs in so its not a bulb prob (LEDs have been in for a while). So I'm think the speed gauge dropping and jumping around is electrical as well. Another strange thing is the radio would just stop working at random times. This seems to be linked directly to the ignition switch as a little wiggle of the key in the ignition and the radio comes back on. This started about 2 months ago.

Wouldn't really care at the speed gauge, but I have to get it inspected soon for my state. Its both a trail and DD rig.
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Old 12-26-2013, 09:10 AM   #17
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Quote:
Originally Posted by WRNGLR View Post
sorry for thread jack but
I have the same trouble with mine, however, my speedo is a sensor and tone ring ( came with Mega Short SYE ) not a gear /spline setup.

I have replaced the sensor once before and the problem went away for a while but now it's back head is getting sore, will be watching with interest.

cheers
Greg
Check out this thread for the RR Mega Short SYE. Most likely your nut is loose.

Rugged Ridge mega short SYE retaining nut size???
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Old 04-11-2014, 08:38 PM   #18
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Typical forum... no answer to his problem... just alot of Blah blah blah... I think its this, I think its that... Oh yeah, mine does it too.... oh yeah My friends does it too... blah blah blah... * IF YOU DONT HAVE A LOGICAL ANSWER TO HIS ( OR ANYONES QUESTIONS ) SPARE THE COMMENTS !
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Old 04-11-2014, 09:44 PM   #19
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Typical forum... no answer to his problem... just alot of Blah blah blah... I think its this, I think its that... Oh yeah, mine does it too.... oh yeah My friends does it too... blah blah blah... * IF YOU DONT HAVE A LOGICAL ANSWER TO HIS ( OR ANYONES QUESTIONS ) SPARE THE COMMENTS !
It's your muffler bearing.
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Old 04-11-2014, 09:52 PM   #20
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Maybe you should post in the tech forum if you don't want general discussion.

Edit I intended that for the forum basher guy. He's not OP. He's obviously mad his uncles mothers brothers father knows more about Jeeps than him. Jeep on!
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Old 06-10-2014, 02:49 PM   #21
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Fixed!

Quote:
Originally Posted by coley View Post
Check out this thread for the RR Mega Short SYE. Most likely your nut is loose.

Rugged Ridge mega short SYE retaining nut size???
Sorry a bit late on replying, but yep, this ended up being the issue. Retorqued and all is perfect again. RR did send me a shim just in case, but holding on to it for now.
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Old 06-11-2014, 04:36 AM   #22
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That is strange, Jeeps don't have the cable it is all wires...
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Old 06-11-2014, 07:27 AM   #23
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I figured out after messing with mine for months that the nut just won't hold it perfectly tight forever. It all comes down to which way I rotate it when meshing the teeth against each other. If I rotate one way it eventually gets worse. If I rotate the other (counter clockwise), instead of getting looser it gets tighter and all bouncing disappeared. Been good for about 6 months now.
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Old 06-11-2014, 12:17 PM   #24
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Sorry a bit late on replying, but yep, this ended up being the issue. Retorqued and all is perfect again. RR did send me a shim just in case, but holding on to it for now.
Cool. Glad I could help.

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