Demonhead

Hey guys, I need help finding out what kind of transmission I have. I'm not the original owner so I dont know what he did to this. The problem started when I found the VSS unhooked. I hooked it up and ran the car. The speedometer seemed to read almost twice as my actual speed, it also makes the odometer run quicker. So I took out the VSS and went to autozone to get a new one. Supposedly, my year only offered mechanical VSS while the one I pulled out was electronically operated.

I cannot find any VSS for my vehicle that looks like the one that I pulled out. Maybe if I find what my transmission is I can find the right one.

cliffyk

It's a Tremec 3650, TR-3650-3-TCET1789 to be exact--standard fare for the '01-1/2 through '04 model years.

Your car came with a Tremec T-45 which sends 6 pulses per output shaft rotation, the 3650 sends 12 pulses/rev. To fix it you will need to get a Dallas SpeedCal, or something similar--the universal speedoDRD ($70) should also work, I use one of these on my bike.

Demonhead

Scratch the double reading, I replugged today to double check and when I was driving out of my drive way, about 3-5 mph and speedometer read around 15-20.

Does your solution still apply?

cliffyk

I flubbed a bit too, it is the automatics that have the 6 tooth reluctor wheel, not the T-45--that's what happens when you are my age and rely on memory instead of looking things up. I do not have any specs for the T-45's # of pulses/output shaft revolution.

The speedoDRD could handle that in it's ratio mode.

Demonhead

Scratch the double reading, I replugged today to double check and when I was driving out of my drive way, about 3-5 mph and speedometer read around 15-20.

Does your solution still apply?

Demonhead

Thanks a bunch man, I'm going to give Dallas Mustangs a call and see what they can do for me.

cliffyk

With a bit of late night research I found that the speedometer on your '98 expects 8000 pulses per mile (ppm) from the output shaft sensor (OSS) on the transmission. This bit of information lets us validate the error--which is always nice.

As stated above your '98 speedometer expects 8000 ppm. However the 3650 sensor outputs 12 pulses per output shaft revolution, and as the tires turn 810 revs/mile and the final drive gears are 3.27:1, this makes the output pulses per mile for the 3650 equal:

810 * 3.27 * 12 = 31784 ppm.

Since this is 3.97 times faster (31784 / 8000) than the 8000 ppm expected by the speedometer, it reads 3.97 times fast making 5 mph in your driveway display as 5 * 3.97 = 19.9 mph.

The SpeedCal (or speedoDRD) can fix it.

Demonhead

Very impressive cliffyk, thanks for your help. Ive been surfing around the internet for this reason and no one seemed to have an answer with a valid reason behind it.
Thanks again man!