Hello! I have just taken the 5.7 engine and transmission combo out of a 95 G30 that spent its life as a shuttle bus and installed it in my 96 G30 cargo van. Same engine/transmission. Now the speedometer is about 12 mph too fast. In other words, when it shows 50 mph I'm actually going about 38 mph. I'm guessing my Cargo van has a lower rear axle gear than the shuttle bus? How do I verify what my axle ratio is and how can I get it right? I think its electronic but is there a part I can take off the original transmission and install on the new one? Thanks in advance for any help. I can't seem to find anything reliable from Google.

 

the gear ratio is often stamped right into the ring & pinion gears. Otherwise, just jack up the rear and turn the wheels and count how many times the driveshaft turns. It's probably also on your RPO sticker.

As for correcting the speedo (if you're really that worried about it. I wouldn't be), then speed is taken from the transmission output. If it's an OBD2 vehicle (96 is on the cusp I think. It could be either way) then you would have to reprogram the computer. But it's a 27yo vehicle ... I wouldn't bother. Just do the math in your head.

 

Where would the RPO sticker be? I've read that in trucks it is in the glove box but not mine.

 

I've heard glove box as well. Later on GM put them in the door jamb.