I have a 1985 Trans am with a 700r4 and a 9 bolt rear end. What gears do I have in my rear? How do i tell what my car has?

 

Could be 2.77, 3.27, or 3.45 gears.... hard to say. 3.45 only came in the manual trans cars far as I know, so that only leaves you with the other two **if its all stock and original** anything could have been changed in the last 23 years.... I changed the rear end in mine 3 times in the last 2 years, and the pervious owner did it at least once that I know of too.

Only way to know for sure whats there is to pop off the cover and count the teeth on the ring and pinion gears.

 

Do i have to take anything apart besides the cover off. How does counting the teeth tell me what gears i have. how many teeth will they both have

 

next time you drive, do 60 mph and note the rpm in 3rd gear.. it will be easier to tell.. 3.27's will be about 2700rpm.. 2.77's will be down around 2300

 

Just take the cover off and count the teeth.It's the best way to find out.You can also look for the numbers stamped on your gears.

 

LG4 with atuo a 3:08 9-bolt std or option 3:27.

 

I'll give you an example of how counting the teeth works... the gear ratio is the result of some math being done, between the ring gear and pinion gear.

For example - if you count 41 teeth on the ring gear, and 10 on the pinion gear, then 41/10 = 4.10

That would be a 4.10 gear ratio.

41 teeth and 11 teeth would be 41/11 = 3.73 gear ratio

Those are 10 bolt and 12 bolt rear end gear sets I mentioned above, the 9 bolt may use different numbers of teeth, but the math still applies the same.

Thats why you count the gear teeth to figure out the ratio you have. You only have to remove the cover to do it, and its probably due for a rear end oil change anyway, so do that at the same time.

 

If it's down to 2.77 or 3.27, then raise the rear end of the car, put it in neutral and turn the driveshaft by hand until the wheel(s) go around once. If it's single-trac then leave one wheel touching the ground.

 

Just drop the pumpkin and count them by hand. This way you can change the fluid in the rear end while youre at it

 

Jack up the car.

Put in neutral

mark the drive shaft

mark the tire

turn the tire 10 revolutions by hand

count home many times the drive shaft turns

divide by 10