TH125 Auto Transmission Speedometer Gear Changes (Page 1/1)
pelensky
APR 23, 08:33 PM
I have a mostly stock 1988 GT with the 3 speed auto TH125 transmission. It currently has slightly taller tires than stock and the speedometer reads 3 mph low at 60 mph gps. I would like to change the speedometer gears in the transmission. What is the stock gearset color and teeth count? What should I install to get closer to the actual speed? Where can I buy these gears?
theogre
APR 24, 02:19 PM
GM did make some speedo gears but many are hard to find. New gear may work or have different errors. Meaning speedo and ECM reads more too slow or too fast.
Is/was an aftermarket module to "dial in" many setups but not sure if they work for VSS used in OE Fiero. Many where for Optical VSS to Generator VSS for switching 4T60 etc w/ Optical VSS into Fiero and others.
Changing gears means messing w/ the Trans Governor. If you mess up that the Trans won't shift right or not shift until you have a trans shop to fix it.
Tall tires affect total gearing not just speedo and get a bit better MGP but hurts HP. See my Cave, Gear Ratio
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
