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Speedo needle wobbles


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In the 89 MJ, two problems have occured:

 

The speedo needle wobbles at lower speeds, (and according to my radar it is about 10 MPH off slow) without having changed tire size or having any lift on the truck. The trans and diff are what came with the vehicle. Speedo cable is new. I realize the speedo gear is probably the culprit, but can there be another reason? Where does one get new gears? How do you choose which one to get?

 

The gas gauge is pegged full right, and was previously working properly. Truck runs great, has 40 PSI at the rail. Ground at left rear is good. If it is the sender (have not yet checked OHMs yet) where does one get that item?

 

Thanks

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You can set the speedo needle to match the vehicle speed. I've done this on a few vehicles (after cluster swaps) and it's fairly easy but requires patience. Pull the plastic face off the cluster but leave the gauges in the truck. If the speedo is 10mph low pull the needle off the face, move it up about 10 degrees, and put it back on the pin. Take the truck on the highway and bring a stopwatch. Get to 60mph indicated and time how long it takes to go from milepost to milepost. If you're reading 10mph low your indicated time will probably be somewhere around 53 sec. When I did my current MJ I stopped when I managed 59.97 sec, which I thought was pretty darn good.

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You can set the speedo needle to match the vehicle speed. I've done this on a few vehicles (after cluster swaps) and it's fairly easy but requires patience. Pull the plastic face off the cluster but leave the gauges in the truck. If the speedo is 10mph low pull the needle off the face, move it up about 10 degrees, and put it back on the pin. Take the truck on the highway and bring a stopwatch. Get to 60mph indicated and time how long it takes to go from milepost to milepost. If you're reading 10mph low your indicated time will probably be somewhere around 53 sec. When I did my current MJ I stopped when I managed 59.97 sec, which I thought was pretty darn good.

Very bad idea.

 

Now how far off are you at 30 and at 45 and at 75?

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In the 89 MJ, two problems have occured:

 

Speedo cable is new. I realize the speedo gear is probably the culprit, but can there be another reason? Where does one get new gears? How do you choose which one to get?

Thanks

 

Here's a couple of references for the speedo gear:

http://motionoffroad.com/catalog/index. ... x&cPath=14

http://www.quadratec.com/jeep_knowledge ... cle-46.htm

http://www.rocky-road.com/calculator.html

http://www.jbconversions.com/index2.php?pc=1

 

As far as the fuel level sender. It sounds like the float is simply stuck in the "Full" position. Have you banged on the tank - (not hard enough to cause a spark though)?

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Thanks fpr the replies. I'm gonna have to determine which gear to get, and the info is all there.

 

I shook the truck like a wet dog (from the left rear quarter panel) and the gas gauge started woking again. I guess the float was stuck. I really don't wanna mess with it until I can secure a replacement (in case I mess up!)

 

Thanks again.

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I would not recommend removing the speedo needle from the gauge. If you want to adjust the speedo reading, change the speedo gear.

:agree:

 

You can't correct speedo error by moving the needle ... unless someone else "fixed" it that way before and you're un-fixing the "fix." Speedometer error is not a fixed number of MPH, like "5." It's proportional. If your speedo reads 2 MPH low at 25 MPH, then it'll be 4 MPH low and 50 and 6 MPH low at 75. The only way to correct it is by swapping speedo gears until you get the one that comes closest to being accurate.

 

Remember that it's very rare to be dead nuts on. The factory typically used one speedo gear to cover two or three tire size/axle ratio combinations. If one of them was right ... the other two had to be wrong. You just want to get close. I prefer to have my speedo read a little high, so if I drive at the speed I'm seeing on the speedo, a cop with a radar or laser gun should hopefully read a couple of MPH less.

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:agree: X 3. Jake, DO NOT pull the speedo needle in an attempt to calibrate the gauge. Bad idea for sure. The speedo is a non-linear gauge, and it won't work accurately over the full scale. This is the best most accurate site to calculate the correct speedo gear for your rig (mainly because I has a bit in putting it together :D ) and includes gear part numbers for all models and links where to get them.

 

http://gojeep.willyshotrod.com/HowtoSpeedoGears.htm

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Thanks guys, but it was never my intention to 'adjust' the needle on the gauge. Once I determine the exact gearing for the rear end I'll use the handy charts here in the post to find the right gear.

 

Having a radar in my unit helps considerably, and Eable is absolutely correct about the differential speedometer difference. At 15 MPH indicated, the radar reads about 19-20, but when he shows 35 MPH on the gauge he is actually going at about 45.

 

If I can't get one that reads really close, I (once again) agree with Don, I'll go for one that reads a little higher then actual.

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Thanks guys, but it was never my intention to 'adjust' the needle on the gauge. Once I determine the exact gearing for the rear end I'll use the handy charts here in the post to find the right gear.

Good for you, but 1987Comanche advised pulling the needle off, and my and Don's advise NOT to do this was in response to that post.

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