The Dodge Challenger Message Board

Ok I bought my car from someone in Florida that converted it from a 318 to a 440. I do not know if the gears were changed but I have a hunch that they were. I think this because both my tires burn off the launch so I assume I have a sure-grip. I know it is an 8 3/4. Any guesses on what gear ratio it may be? There are no identifying markers on the car so I can't tell by a number code.

EDIT: I have an automatic transmission. It is the A-727 originally it was the A-904

I think this has been covered many times in this section. It might be worth your while looking through it and seeing the other posts.

But to quickly answer you.

Put the car on axle stands so that both rear wheels are off the ground. have the trans in neutral.

Turn one wheel.

If the other wheel turns the same way you have a sure grip LSD.
Count the number of times the driveshaft turns to get one turn of the wheel. That is your gear ratio.

If the other wheel goes in the opposite direction you have an open diff (no sure-grip)
In this case count how many times the driveshaft rotates for every TWO turns of the rear wheel. That is your gear ratio.

On the nose of the diff (drivers side) there is a number cast into the casing. This part number is the type of 8.75 (or whatever) diff you have.

The numbers in the casting Dave is referring to should be one of three "741", "742", or "489". "489" being the most desired, but all are good pigs or center sections.