Are the speed seonsors / governors mated with the transmissions? My tranny came off of a 1988 caddy fleetwod with 4.5, i have an 87 dveille with 4.1. teh governors and speed sensors on both different, when i installed the 4.1 governor in the 4.5 tranny my speedo would jump from 0 to 4, back to 3, then to 5, back to 0, and so on, and the speed wouldn't be accurate at all. So i thought ok, maybe i'll put the 4.5 governor/speed sensor back in, the connector wires were same colour, but the plugs were slightly different, so i did it anyway. NOW, when i'm rolling in drive idleing, it says i'm going liek 50 km an hour, and if i go about 40km/h it says i'm going 250km/h, when i do city speed, about 40MPH (60, 70km/h), it stays at 0, my mileage jumped 2500 kilometers in 2 days, WTF!!! help me out here please. I'll make a video tonight, so check back. Because of this my tranny doesn't shift right, i'm really pissed off.

I suspect you have different transmissions. wiki (http://en.wikipedia.org/wiki/Turbo-Hydramatic_125)

One unique feature of [the 440-T4] transmission is its use of both a modulator valve and a throttle valve (TV) cable. Most transmission either use one or the other to control shift points and shift smoothness. On the Turbo 440-T4, the TV cable exclusively controls the shift points, while the modulator valve controls the shift feel. This feature makes it very easy for a home, "shadetree" mechanic to adjust the transmission shift points with minimum affect on the shift feel.

The 440-T4 was later renamed the 4T60.

The electronically-controlled 4T60-E was introduced in 1988. By 1991, all 4-speed front wheel drive automatic GM cars used this unit. It would become the basis of the GM 4T65 transmission, still used today.

Looking at my '85 FSM it shows the speedo module connecting to the speedo gear with a simple ring (an O ring?), and a retainer holding it to the governor. I assume this allows the gears to be changed while keeping the speedo module.

If they are different trannies then I would think you'd have to use the module for your computer. However the governor is probably generating a different signal if one of them is electronic and the other is mechanical.

hhmm, both trannies use a modulator valve and a TV cable, but i am going to put my other governor back in, this is just rediculous,