My brother's T/A had a 3.23 rear , recently changed to a 3.08 posi. Does the speedo now read faster or slower?

 

The gear on the transmission output shaft didn't change. It still turns the same rpm as with the original rear end (at a given engine rpm). The rear end gears are now "higher" so the car is going faster than the speedometer reading. It's like putting taller tires on the car. Get on an interstate where you have the mile markers. Drive a few miles and compare your odometer to the distance traveled by the mile markers. Your odometer miles should be less than the mile marker miles. Try it.

 

My car has 3.42s installed and the speedometer reads faster than you are actually going. This means my odometer miles have been racking up faster as well?