How do I find out what gearing I have in the rear end, as I am curious? 1975 L48 auto. I would consider them to be hiway gears, long between shifts, only 3 shifts till top end of 120mph+ I have no idea what other info you would need to figure it out, and as far as I know it is original! Thanks!!

Gerry

gmacp said: How do I find out what gearing I have in the rear end, as I am curious? 1975 L48 auto. I would consider them to be hiway gears, long between shifts, only 3 shifts till top end of 120mph+ I have no idea what other info you would need to figure it out, and as far as I know it is original! Thanks!! Gerry

On the bottom of your housing there is a number stamped.
The 2 letter prefix will tell you what ratio is in the differential.
There were 6 different ratios in 75, the rest of the stampingplant and build date.

if indeed it is orignal gearing then you can just look at the axle codes

http://www.lpcinc.us/axlecodes.htm

the axle code is on the bottom of the differential

if not.. i posted a thread a while back that allows you to determine your gearing with a tape measure and a crayon.

http://www.c3vr.com/vrforums/message_go.asp?MID=41879

this is the link to the spreadsheet i built for doing this

http://www.direclynx.net/~cthulhu/corvette/charts.html

daveb12 said: On the bottom of your housing there is a number stamped. The 2 letter prefix will tell you what ratio is in the differential. There were 6 different ratios in 75, the rest of the stampingplant and build date.

72-75
Positraction 3:36 Ratio
AX

72-75
Positraction 3:36 Ratio
LR

72-75
Positraction 4:11 Ratio
AC

72-75
Positraction 3:70 Ratio
AB

72-75
Positraction 3:55 Ratio
AA

72-75
Positraction 3:08 Ratio
AW

Thanks everyone! I will be checking this out the next time I see HIM!

The original rear axle with your car was a 3:08. That doesn't mean someone hasn't changed the gear.

Lift both rear wheels off the ground. Mark their positon. Mark the drive shaft position. Put the car in neutral. Turn the rear wheels one turn. Count the turns the drive shafts makes during that one turn. The number of drive shaft rotations is the gear ratio. While this is not exact, carefully done it will get you close enough to match up to one of the available ratios, and know what you have.

Ben was working on a method of measureing by wrap up on the drive shaft while turning one turn of the rear wheels. You can check some older threads.

kstyer said: Ben was working on a method of measureing by wrap up on the drive shaft while turning one turn of the rear wheels. You can check some older threads.

thread listed in post above..