Is it very difficult to change rear end gears from 3.15 to 2.73.
Fred

 

Its rare that someone would want to do that. Are you thinking fuel economy?
If you pick up a complete diff, its not complicated, but a bit of work. If you're talking about replacing the ring and pinion in your existing diff, your going to need a little expertise and several other refresher items (seals and stuff) as well.

 

...and here I am wanting to go shorter ratio than my 3.15!!
You will gain a tiny amount of maximum fuel economy, but loose acceleration at all times, and torque when on hills..Think of going southtbound on the I-5 out of Portland in the Terwillerger Curves, the long uphill..you might have to leave 4 th to keep the load in the cam range of the engine. With 3.15 it is is no sweat.

Yeah, I'm in the Portland area too!

 

C5 Gear and final drive ratios

M6 >R&P 3.42 >Final drive ratio
1st Gear 2.66:1 =9.0972:1
2nd Gear 1.78:1 =6.0876:1
3rd Gear 1.30:1 =4.4460:1
4th Gear 1.00:1 =3.4200:1
5th Gear 0.74:1 =2.5308:1
6th Gear 0.50:1 =1.7100:1
Reverse 2.90:1 =9.918:1

Z06/M12 >R&P 3.42 >Final drive ratio
1st Gear 2.97:1 =10.1574:1
2nd Gear 2.07:1 =7.0794:1
3rd Gear 1.43:1 =4.8906:1
4th Gear 1.00:1 =3.4200:1
5th Gear 0.84:1 =2.8728:1
6th Gear 0.56:1 =1.9152:1
Reverse 3.28:1 =11.2176:1


A4 >R&P 2.73 >Final drive ratio
1st Gear 3.06:1 =8.3538:1
2nd Gear 1.62:1 =4.4226:1
3rd Gear 1.00:1 =2.7300:1
4th Gear 0.70:1 =1.911:1
Reverse 2.29:1 = 6.2517:1

A4 Option >R&P 3.15 >Final drive ratio
1st Gear 3.06:1 =9.639:1
2nd Gear 1.62:1 =5.103:1
3rd Gear 1.00:1 =3.150:1
4th Gear 0.70:1 =2.205:1
Reverse 2.29:1 =7.2135:1

A4 CUSTOM with M6 or M12 differential
A4 >R&P 3.42 >Final drive ratio
1st Gear 3.06:1 =10.4652:1
2nd Gear 1.62:1 =5.5404:1
3rd Gear 1.00:1 =3.4200:1
4th Gear 0.70:1 =2.3940:1
Reverse 2.29:1 =7.8318:1

Of course, R&P is "Ring and Pinion"

Your current final drive ratio is 4th Gear 0.70:1 =2.205:1, if you went to the 'stock' A4 economy differential, it would be 4th Gear 0.70:1 =1.911:1 that is quite a big difference in actual feel of how a car responds to throttle.

 

Honestly, Id keep the 3.15's. They are a great medium between efficiency and performance. You can still get 30mpg on the free way with them. My 3.42's are getting me 28-29. You are not sacrificing much at all economically, and will never save enough on fuel to make up for the cost of the change over.

P.S. Oregon native here too

 

Before I started modding the vert I was running 3:15s and it averaged a little over 31 at 75-85 on the road. I really doubt you will be happy with the difference in performance for the tiny bit of extra fuel mileage.