how do you find the gear ratio on a gm bolt rear end?

Question

its a 10 bolt 79 firebird rear end

Answer 1

On the GM rears they have a metal tag that is attached

Answer 2

On the GM rears they have a metal tag that is attached usually by one of the 10 bolts that retain the pumpkin cover. On this metal tag is a 2 letter code. Get a Chilton or Haynes manual and you should be able to look up this code or call the dealer. But, if this tag is missing, sometimes whenever the rear gets serviced the tech maty toss this tag away. So this is what you can do. Put the car in the air , both wheels off the ground. Mark a liner with a piece of chalk on the bottom of the driveshaft. Go to the rear tire and make a note of where the valve stem is pointing. Have a friend turn the wheel one complete revolution until the valve stem is in the original location from where he started to turn the tire. The meantime while he turns the tire 1 revolution , you count how many times that chalk mark goes a full 360 degrees. If the driveshaft goes 3 times around for each tire revolution, then your gear ratio is 3:08, if the driveshaft goes 3 1/4 turns then the ratio is 3:23, 3 1/2 times then it is 3:55, 3 3/4 turns and it is 3:73 4 times and it is 4:11.
Get the idea? It may not be accurate but it is very close.
Good Luck

Answer 3

most have been answered a above me you mark the drive shaft and the wheel jack up of coarse and turn the tire one revolution and count how many times the drive shaft turns and divide the two and you will have you ratio but in doubt all gears are stamped and matched ring and pinion together change a a set always, hooper rear end supply in the San Fernando Vally have use like new refinished rear ends in ca, give em a call they will even trade you set for set sometimes good luck, the tags are in code most of the time and they will help with that as well, if you don't want to take it a part do the simple way take care

Answer 4

easiest way is to jack the rear end up off the ground and turn the drive shaft you will need to mark the tire and the drive shaft count the number of times the mark on the tire comes around compared to the number of times the mark on the drive shaft comes around or you can clean the grease off the serial # plate and it should tell you it may have a series # on it then you ll need call the dealer to get the ratio

Answer 5

Step UP and do the right thing. Take the 10 bolts out, drain the fluid (you know it needs it) and count the teeth. It might even be stamped on the ring.

Answer 6

listen to mailbox 1024