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01-26-2009, 06:04:18 PM
so my 79 camaro has stock 10 bolt with stock gears in it and I wanted to upgrade to a 3.73. I have heard that it is best to have this professionaly done. What do I need to change the gears to this ratio and does anyone have a ballpark estimate on cost. Thanx

01-26-2009, 06:24:53 PM
Gotta know a few more details......

Are you adding posi with the gear swap or just changing gear ratio on an "open" rear?

What gear ratio do you have currently?

01-26-2009, 06:33:27 PM
I believe that it is 2.43 and if i can install the 3.73 gears without adding a posi than im sure that would be cheaper. I am unsure whether or not there is a posi on it or not because the car is at home and i am currently at school.

big gear head
01-26-2009, 09:09:21 PM
You need to get a 3 series differential. The one that you have now is a 2 series and you need a 3 series for the 3.73 gears. It is always a good idea to upgrade to a posi when adding performance gears, but it is not nesecary. You will need a good installation kit.

There are several special tools that are needed to correctly set up a ring & pinion set. You also must know how to set the pinion depth, bearing preload and backlash. You must know how to read the contact pattern so that you will know what adjustments need to be made to the pinion depth.

I know that someone is going to come along and tell you that you can use a ring gear spacer on your 2 series differential and install the 3.73 gears on it. I never recommend a spacer. I have seen too many rear end failures caused by spacers.

01-26-2009, 11:13:42 PM
You can use a ring gear spacer with your carrier. ;)

Yeah, BGH, I understand the risk of adding another shear point to the mechanics of the system.

The part is produced for this modification and my son's car is built this way.
He has had no problems but.... It isn't built to the hilt for racing either.

I think Freddies point is:
Using a spacer is not as good as using the proper gear with the intended carrier.
You are adding a potential point of failure and another variable to the final setup of the gear mechanics. (Depth/backlash)

If you have an open rear end now and want to go with a posi rear, You must change the carrier anyway. A wise man would do this with the right parts and do it ONCE!

01-26-2009, 11:14:58 PM
3.73s with an open is a waste, you will blow one tire away and not go anywhere from a launch

big gear head
01-27-2009, 01:26:53 AM
TM, have you seen these pictures? I can't remember if I have posted them here before. This is one of several reasons that I don't like the spacers. Click on the pictures and you will be able to see what I mean.
http://thumb7.webshots.net/t/73/73/1/95/63/2948195630041712107Ppjwnf_th.jpg (http://rides.webshots.com/photo/2948195630041712107Ppjwnf)
This is a 2 series Auburn. Notice the machined area next to the ring gear flange. This is what centers the ring gear on the differential. The ring gear is a press fit around this area.
http://thumb7.webshots.net/t/69/669/3/44/32/2920344320041712107HpdQSw_th.jpg (http://rides.webshots.com/photo/2920344320041712107HpdQSw)
This is the same Auburn with a spacer installed. Notice that the area that centers the gear almost disapeared. The ring gear has a chamfer on the back which means that none of the gear will be touching the area that it's suppose to be pressed onto. There is nothing left to center the gear and the gear will float around with nothing but the loose ring gear bolts to hold it in place. This will cause big problems with the gear pattern and wear. This is something that most people never notice when they install a spacer.

Not all of them are as bad as this one. I'm not trying to be hard to get along with. I just like to keep people from messing up the expensive gears that they just purchased.

01-27-2009, 09:14:41 AM
Good pics, Freddie!!!
I see the potential problem and I wouldn't use them either.

(I actually bought an Eaton posi and RG/Pinion from you, Freddie. I trust your advice on this one.)

If the original poster wants to go with a 3.73 RG/P without swapping the carrier, It's possible..... But not recommended. ;)

(Kinda like air shocks for raising the rear... they work, they're cheap.... but they aren't the way to go about it right. :eek: )

A 3 series posi carrier and new gears would be a wiser move if he's gonna tear into it, IMO.

01-27-2009, 09:23:45 AM
By your screen name, I assume the car is a Z28. If it is a real Z and the rear has not been changed, 2.43 ratio was not available. Are you sure it isn't a 3.42? This is the stock (and only) ratio available in 1979 for the Z28 with auto trans. This would also be a posi (limited slip) rear if original. If you do have a 3.42 rear, I don't think you will see enough difference to justify the change to 3.73 unless the rear is in need of repair/replacement. Good luck.