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Discussion Starter #1
Those are the tires recommended in the car's manual and what I have on the car. What other things might cause inaccurate speedometer readings?

The speedometer at lower speeds, around 25, shows a couple MPH off and up to seven MPH off at higher speeds. So at 55 speedometer I'm doing 62, according to the GPS.

A mechanic mentioned replacing the gearing from a ten tooth to a 12 tooth gear. But why would the gearing start reading incorrectly in the first place?

If I place the car on a couple of Rhino ramps can I replace the speed/distance sensor without losing trans fluid due to the incline?

Thanks
 

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Are you saying that this error did not always exist during your ownership of the car?

There are 3 different gears used in the speed sensor - 19, 20 and 21 teeth. I can research which is which, but the colors are blue, yellow and white. Reducing the number of teeth will increase the displayed speed of the speedometer, so if someone has switched the gears in the speed sensor at some point, they may have put the wrong gear in, with fewer teeth (spins faster with fewer teeth). To change the gear, unplug the latched connector on the speed sensor, unscrew the speedometer cable if so equipped, undo the bolt that holds the sensor down, pull the sensor straight up and out of the transaxle, then using two screwdrivers, carefully pry the tangs outward that hold the gear on, and pull the plastic helical gear off. To install, press the new gear in until it snaps in, retained by the tangs. Insert the speed sensor FULLY (press hard) in the transaxle, bolt it back down, plug it in, install speedo cable if equipped, and go for a test drive.

You will not lose fluid on level ground just from removing the speed sensor - maybe a few drops, no more.
 

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Another thought - check the door jamb sticker to see what tires are recommended. And sometimes the sticker is wrong. I bought a 92 Daytona new, and it came with 14 inch tires, but the door sticker said 15 inch.
Running 14 inch if it came with 15 inch will cause the speedometer to read too fast.
 

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Discussion Starter #4
The speedometer use to register correctly but after I used a GPS on a trip I noticed the divergence as I increased speed. The speedometer always reads slower than the GPS. At 25 speedometer the GPS showed 27. At 55 speedometer the GPS would read 62. So in this case a reduction in teeth would be needed but which one to use would be trial and error.

The paper door jam sticker has long ago fallen off but I have always used the 185/70/14 size tire. I have been told by some that after market axles might have a slightly different diameter causing the difference in speed. I have also had the speed/distance sensor replace before so maybe there is the possibility that an incorrect model part was installed (interchange?)

If I place the car front on two Rhino ramps the car won’t be level. The front end will be about eight inches higher than the rear. So I suspect I would dump a bit of trans fluid doing it myself.

I have another S/D sensor I want to install. Is there any way from looking at it to determine if it has the correct gearing or is the only way to know would be to open it up?

Thanks
 

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Might help if you could post the year, make and model.
 

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There is a 19 tooth and 20 tooth speedo gear both listed for 14" tires. The 19T is listed for power steering w/ Michelin WSW (whitewall) tires. I guess that the Michelin tire profile was somehow taller than the generic 14" tires? See figure 21A-2900 (with part numbers) here:
http://oskin.ru/pub/chrysler-dodge/manuals/Chrysler_Service_Parts_Catalog/CD2/82-96PassCar/87p.PDF

The speedometer gauge itself may have become inaccurate. Only the optional 125 mph speedometer was 'Certified' and used in police/public safety duty K & E-body packages to clock other vehicles. Clusters are shown on figure 8A-1510.

The speed/distance sensors rarely get inaccurate. They either work or they don't. The driveaxle worm diameters are all the same. A good sensor has 8 pulses per revolution. It can be watched with a meter.
I have seen 7 pulses from a defective one. That would automatically reduce the indicated speed by 12.5%.
 

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The speedometer use to register correctly but after I used a GPS on a trip I noticed the divergence as I increased speed. The speedometer always reads slower than the GPS. At 25 speedometer the GPS showed 27. At 55 speedometer the GPS would read 62. So in this case a reduction in teeth would be needed but which one to use would be trial and error.

The paper door jam sticker has long ago fallen off but I have always used the 185/70/14 size tire. I have been told by some that after market axles might have a slightly different diameter causing the difference in speed. I have also had the speed/distance sensor replace before so maybe there is the possibility that an incorrect model part was installed (interchange?)

If I place the car front on two Rhino ramps the car won’t be level. The front end will be about eight inches higher than the rear. So I suspect I would dump a bit of trans fluid doing it myself.

I have another S/D sensor I want to install. Is there any way from looking at it to determine if it has the correct gearing or is the only way to know would be to open it up?

Thanks
There is no reason to put the car on ramps. The speed sensor can be reached from above with little trouble.

As to aftermarket axles, did you replace them? And no, a reduction in teeth would increase the displayed speed. You want to reduce displayed speed, so you want to go up in the tooth count.
Speedometers inherently have as much as 4% error. Yours appears to be a +12.7% error, though.
 

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19-tooth is yellow, 20-tooth is blue, 21-tooth is white.
 

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Sorry, I got this backwards. At 55 indicated, you are reading 62, not the other way around. So it's reading low, and in that case, you do want to reduce the number of teeth.
I think IC has it right about the speed sensor itself being bad, not the gear.
 

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Discussion Starter #11
There is a 19 tooth and 20 tooth speedo gear both listed for 14" tires. The 19T is listed for power steering w/ Michelin WSW (whitewall) tires. I guess that the Michelin tire profile was somehow taller than the generic 14" tires? See figure 21A-2900 (with part numbers) here:
http://oskin.ru/pub/chrysler-dodge/manuals/Chrysler_Service_Parts_Catalog/CD2/82-96PassCar/87p.PDF

The speedometer gauge itself may have become inaccurate. Only the optional 125 mph speedometer was 'Certified' and used in police/public safety duty K & E-body packages to clock other vehicles. Clusters are shown on figure 8A-1510.

The speed/distance sensors rarely get inaccurate. They either work or they don't. The driveaxle worm diameters are all the same. A good sensor has 8 pulses per revolution. It can be watched with a meter.
I have seen 7 pulses from a defective one. That would automatically reduce the indicated speed by 12.5%.


I'll replace the speed sensor and see if it was defective seeing how the 12.5 percent fits your 7 pulse defective SD sensor.

Thanks again
 

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Discussion Starter #12
Sorry, I got this backwards. At 55 indicated, you are reading 62, not the other way around. So it's reading low, and in that case, you do want to reduce the number of teeth.
I think IC has it right about the speed sensor itself being bad, not the gear.
There is no reason to put the car on ramps. The speed sensor can be reached from above with little trouble.

As to aftermarket axles, did you replace them? And no, a reduction in teeth would increase the displayed speed. You want to reduce displayed speed, so you want to go up in the tooth count.
Speedometers inherently have as much as 4% error. Yours appears to be a +12.7% error, though.

I did not replace the axles myself.

Having been under the car on those Rhino ramps, for me it seems easier to access the SD sensor from below. Going in from the top I'll have to remove the air filter box, be careful of a few cables, and a couple of vacuum lines off the power brake booster. Besides my arm length may be a bit shorter than yours. But I'll give it a try.

I don't see it mentioned in my repair manual but do I need to use and sealant on the Speed/distance sensor when installing it?
 

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No, no sealant, but there is an O-ring. Make sure it's intact when reinstalling. It does take a little effort to lift the sensor out. I pried it with stubby screwdrivers the first time.
 

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Discussion Starter #14
pitb1.JPG
pitb2.JPG



Well, in my opinion the gear looks green. I guess the trans fluid could have altered the color a bit but it isn't white or yellow. At least it has 20 gears.

It looks like some type of sealant was applied to the inner boot around the O-ring. I found the retaining bolt fairly loose and it and the cable drive were loose enough to remove by hand.

Hopefully having the 20T count the sensor itself was bad. We'll know soon enough.
 

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Discussion Starter #15
The new sensor made no difference. Exact same readings.

Should I try one of the 19 tooth gears? The two 19 tooth's had the same part number for a 15 in and 14 inch wheel.

4269 950 1 19 Teeth w/P185/75 R14 P/S W.S.W. Michelin

or

4269 950 1 19 Teeth, w/15" Tire

and is it even possible to find either one?
 

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That's blue, just aged out so it looks green.
Someone has screwed with it, based on there being a sealant on it. So you can't trust what gear you find there. However, with a 12.7% error, going to 19 teeth will only correct it about 5%. And you said it was not always off, but became erroneous. I still think there's a problem other the gear.
Have you checked the odometer while driving a mile against the highway markers that indicate a mile? I would expect a 12.7% error in the odometer as well.
Wondering if a gear in the odometer is partially stripped. They are famous for losing teeth, and if so, eventually stop working altogether.
 

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Discussion Starter #17
That's blue, just aged out so it looks green.
Someone has screwed with it, based on there being a sealant on it. So you can't trust what gear you find there. However, with a 12.7% error, going to 19 teeth will only correct it about 5%. And you said it was not always off, but became erroneous. I still think there's a problem other the gear.
Have you checked the odometer while driving a mile against the highway markers that indicate a mile? I would expect a 12.7% error in the odometer as well.
Wondering if a gear in the odometer is partially stripped. They are famous for losing teeth, and if so, eventually stop working altogether.
I checked the odometer today and it was spot on with the road markers measured over a three mile distance.

Not sure if the speedometer would indicate something should a gear tooth be missing. It moves smoothly in all ranges.

I doubt I'll tear apart the front panel to get to the cluster. I will just have to live with it but at least I know what the readings are actually doing now.
 

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If the odometer is reasonable correct in measuring miles traveled, but the speedometer is incorrect, then the problem is in the speedometer head.
I would replace it. You can swap your odometer assembly from one speedometer to another to keep mileage correct.
Alternatively, and probably more expensive, a speedometer shop can probably fix yours.But there probably aren't many of those shops around now.
 
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Discussion Starter #19
I don't have the energy to even think about tearing down my panel. But I may call the police department and see who they use to calibrate their speedometers to see if anyone remembers how to work on a 32 year old car.
 

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You’ll probably find it’s a lot easier than you think to remove the speedometer.
 
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