well I am instlling 4:10 posi unit in my 87 trans am and was wondering if anyone knows what speedo gears I will need to get my spedo back to reading corectly.

I have a t-5 and it usses the electronic driven spedo I think the gear on the trans shaft is the same but the one on the end of the sensor is difrent then the vehicals using a cable.

The old gear ratio was 3:23 and the tire size is 275/40/17 witch I think has close to the same diamiter as the stock wheels any help is greatly apreciated. If anyone has GM part numbers it would help even more but color or number of teeth would also be a great deal of help.