ive got a 97 z-28 need the low down of 3.73 gears, what size rear end do i have? rearend has 125k on it,im guessing im gonna need the master install kit.
just wondering,how nice is the acceleration diffrence between the stock gears and the 3.73s thanks..

 

The stock gears for a '97 Z are 3.73. I also have a '97 Z and I only have 75k miles on my car, have a Chiltons manual and a few other books on the car, I do a lot of reading up on my car because Im a girl and I dont have a man that will do all the work for me. The stock gears for that car are 3.73. I was thinking about going 4.11 myself, not sure yet.

 

To my knowledge none of the Camaros or Trans Am came with 3.73's. Here is a list of the break down in RPO codes in the glove box that will tell you what gear ratio is in your car. Check to see which one you have.

In the glove box. It'll be GU2 or GU5.

GU2 : AXLE REAR, 2.73 RATIO

GU4 : AXLE REAR, 3.08 RATIO (V6)

GU5 : AXLE REAR, 3.23 RATIO

GU6 : AXLE REAR, 3.42 RATIO


If your car is an automatic the GU2 is a standard and the GU5 was an optional gear ratio.

 

were are the rpo codes located in the glove box, couldnt find any

 

They are on the door of the glove box. Once you open it up you should see a white piece of paper with a lot of numbers and letters on it. Those are your RPO codes.

There are 2 pics in the middle of the page.
They look like this:
http://www.cardomain.com/ride/798191/7

As seen in the picture my car from the factory has a GU6 code which means that it had 3.42 to start out with. The codes are listed in alphabetical order.

If you don't see that they there is a possibility someone took that out. But I think you can use the vin and pull up a listing of all its RPO codes. Do a search, I thought I remember reading something about that. Also there are manual ways to check the gear ratio too. Shoebox has a way to do it on his site

 

Stock you have a 7.5" ring gear 10 bolt. With Lt1 cars you can also check your console to see what gears you have (if its still stock) If your shift indicator goes to "1" then you have 3.23s if it starts at "2" then its 2.73s.

3.42s and 3.73 are great gears for an A4..You really don't need to go numerically higher because of the steep 3.06 first gear ratio. The 3.42s seem to hold up better in the 10 bolts because they have more pinion teeth than the 3.73s. I forget the exact ratio, but I think the 3.42 have a 41 tooth ring gear and a 12 tooth pinion, the 3.73s have 41/11. It doesn't seem like much of a difference, but I rarely hear of A4 cars breaking 3.42s...I had 3.42s for a long time and just switched to 3.73s in my Strange 12 bolt...Like the 3.73s better for street and strip and they work a little better with my cam. I can only speak from personal experience when I say that my stock 3.42s lasted 10 years of 11 second passes with no breakage. Those with 3.73s in their 10 bolts will have to chime in...

With 125K on it I'd also look at going with a new limited slip, bearings and gears...Check around there are places that sell everything in kit form...It would stink to go thru the trouble of switching gears and then your limited slip fails....

--Alan