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Old 06-10-2013, 02:31 PM   #1
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Speedometer Readings v. Actual Speed with 33's

Just bought a 2004 LJ with 4.88 gears and 33s. On the seven hour drive home, I stuck to 70mph on the speedo, knowing that it can be off by as much as 10 mph. Today, I used an iPhone with a GPS speedometer app. and this is what I found:

80 mph on the speedo = 65 mph!
70 mph on the speedo = 60 mph

Can't remember the rest...

What are your readings v. actual?

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Old 06-10-2013, 02:59 PM   #2
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I just threw my 33s on with 3:73 gears and my speedo is off roughly 8-10 mph. So when my speedometer shows 60 I'm doing about 68-70 mph.

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Old 06-10-2013, 03:00 PM   #3
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Driving on 31's, my speedo reading was off by about 2-3% so it wasn't worth replacing the speedo gear. Where as if I was in your shoes, that would be priority one to change asap.
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Old 06-10-2013, 03:06 PM   #4
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Why not just install a new 42 tooth speedometer gear so your speedometer is accurate again? It only take 5 minutes or so to replace it.
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Old 06-10-2013, 03:25 PM   #5
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I'm having the same problem, but I haven't compared with a gps to get an estimate of the difference yet. Can't a procal fix this?
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Old 06-10-2013, 03:33 PM   #6
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An electronic speedometer calibrator can recalibrate the speedometer but you have to wire it in and it costs more. A replacement speedometer gear just snaps in.
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Old 06-10-2013, 07:47 PM   #7
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Here i was just thinking about the speedometer, but just realized how it is overstating mileage on the odometer too! Where can I get the gear and instructions to change it? I wonder how long the previous owner had it this way?
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Old 06-10-2013, 07:49 PM   #8
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Here's some info to get ya started:

Jeep Parts, Jeep Accessories & Jeep Soft Tops From The Jeep Parts Experts - Quadratec

Also, Jerry was on the mark for the speedo gear type 42 tooth I believe...

And here's the sticky:

http://www.wranglerforum.com/f105/sp...ge-121033.html
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Old 06-10-2013, 08:38 PM   #9
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Depends on what transmission you have also.

My 04 TJ with the 42rle auto read 60 on the speedo and 70 on the GPS. That was with 33" tires and stock 3.73 gears. I never changed my speedo gear, just dealt with it.

Now I am running 35" tires and 4.88 gears. My speedo matches the GPS! Glad I never changed the speedo gear.
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Old 06-10-2013, 08:46 PM   #10
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Quote:
Originally Posted by pekoe1111 View Post
Where can I get the gear and instructions to change it?
Here's a very good site with an accurate speedo gear chart (click on it to make it big enough to read) and great instructions on how to do the swap. Changing Your Jeep Speedometer Gear. All you need is a 1/2" wrench.

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