if i changed my transmission from a automatic to a 3 speed manual, do i have to change the differential, why???

_________________
valiant volare 78'..!!

no

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The answer depends on what rear axle ratio your car has. If it has a 3.23 or 3.55 ratio, then it will be fine with the manual transmission. If it has a 2.76 ratio, the car will be very slow, difficult to drive, and hard on clutches with the manual transmission. If it has a 2.93 ratio, it is a marginal case that will be OK but not excellent.

It's easy to check the actual ratio of the actual axle in the car:

Lift the rear of the car so that one tire is free to turn and the other tire is still on the ground. Block the front wheels so the car cannot move, and shift the transmission into Neutral. Make a mark with chalk on the inner sidewall of the rear tire that can turn. Release the parking brake. Turn the marked tire through two full revolutions and count quarter-turns of the driveshaft by watching the rear universal joint caps as they come to face the ground. Divide the number of quarter-turns by four to get your ratio.

16/4 = 4 = 3.91
14/4 = 3-1/2 = 3.54 or 3.55
13/4 = 3-1/4 = 3.21 or 3.23
12/4 = 3 = 2.93 or 2.94
11/4 = 2-3/4 = 2.71 or 2.76
10/4 = 2-1/2 = 2.45
9/4 = 2-1/4 = 2.26

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

What type of 3-speed manual trans are you looking at? Many are not that strong and do not have a syncronized first gear. If you are going thru the trouble to convert from an automatic to a manual trans, swap-in a 4 or a 5 speed.
DD

Well ok, I wasn't thinking of driveability when I said you don't have to change the differential................

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes