I am new here and I have a 1987 olds cutlass that has a 350 with 4 bolt mains, steel crank, double hump heads, and a gm four speed. I did the vin decoder to try and figure out what the rear end gear ratio was, but it did not say. It is the original rear (not posi) The car originally had a 307 with an automatic in it. I just want to know so that I can get the correct speedometer gear. Which leads to my next question of where to get the speedo gear that goes inside the trans on the shaft. As much power as this thing has it is really easy to speed, also the fact that I am 17 and I have "lead foot itis" does not help. Help please.....

 

check with your mechanic to see if he has any of these parts or may know where to get them in your city/state. Good luck!

 

Pop your trunk lid and find the sticker with all of the option codes on it. Jot down any code that starts with a "G". I don't have the magic decoder ring, but someone here will be able to tell you what the ratio is.

Of course, that only tells you what the original rear end was. How can you be sure no one swapped it or swapped ring and pinion? The only way to be sure of what ratio you have is to drop the differential cover and count teeth.