Engine/Transmission (1994 - 1998) Speedometer Calibration

[biggy238]

I went to my dealership today. . (see "HELP ME transmission and dealership problems")



It took the pros at chrysler 3 hours to figure out that I have the early PCM that will not accept the modified RPM of a taller tire.



My question is IF the compueter can be flashed as per TST mystery switch instructions, will the new PROM give me the new speedometer calibration ability?



I can use a box to calibrate it I know, But I really don't want to go that route. I think I can get them to flash it and recalibrate it for the same price but I need to know if it can be done. Any ideas?

 

[dpuckett]

I got a box for my non-PCM equipped truck for under $50. Dealer wanted $100+. The one I got is within 0. 7%



Daniel

 

[Extreme1]

I bought a different gear for the speed sensor. It was about $8.

 

[Cooker]

I thought they could only reflash the PCM for certain tire sizes? I would guess they cannot flash it for a 35" tire. I agree the gear on the T-Case is the way to go.

 

[John - K5AWO]

I believe that their menu shows only a few "standard" tire sizes.



However, I have a better way to fix it, just replace the speed markings like this:



#ad

 

[biggy238]

ROTFLMAO



If I get new white faces I'll paint a few of those on it.



Where did you guys get the gears? They tried to find one for me locally when they couldn't get it done (they must have really wanted my money) but they couldn't find the new gear.



Let me know if you've got any online gear suppliers.

Thanks

 

[Extreme1]

Mine came from the Dodge parts department. The speed sensor has a gear on it. There is one for the 4. 10 gear ratio and one for the 3. 54 ratio. It is a standard gear that is used on several applications. The trick is finding a parts person that can look up the existing gear and then find a matching unit that has a different number of teeth.



I adjusted mine to correct the speedometer (it was off a little) and the odometer is as close as it was. Cool that they don't agree with stock sized tires, huh?



Note that when you install the new gear, the sensor has to be positioned correctly with regard to the number of teeth the gear has. The positions are marked on the retaining ring.



This will only work up to a certain year ('98?) when a change was made to read the speed from the hall effect type sensor in the rear diff.

 

[Cooker]

You can also buy the gear from Rickson. A couple of them are pretty spendy. The trick is to figure out which one you would need.



http://www.ricksontruck.com/speedometer.html

 

[MDKram]

You need to order a new Speedo Drive gear from DC. The part number is 520676xx where xx represents the number of teeth on the drive gear. My stock tires were 245/75-16 and were replaced with 235/85-16. I changed the speedo drive gear to one with 30 teeth from the stock one which had 31 teeth. My speedo is bang on according to Magellan GPS. I would recommend that you buy a 28 tooth drive gear (i. e. 52067628) which should get you very close. The speedo drive gear is located on the driver's side of the transfer case. Good Luck!

 

[biggy238]

MDKram thank you for that tidbit. I'll probably go that route.

 

[vssman]

Biggy',



When you change the gear, make sure you don't twist the VSS unit when removing or inserting it into the transmission/transfer case. Put a little transmission fluid or oil on the o-ring to aid in re-installing it. They tend to leak with the slightest cut. The original o-rings where coated with a teflon based coating. (I used to make these things for DC's suppler before they went to China... ) You may have to re-orientate the adapeter housing to the transmission/tansfer case depending on how many teeth are on the new gear. If I remember correctly, the fewer teeth gears are on one side of vertical and higer are on teh other side. It's easy to do, and they make several gears for different tire sizes.