9formula4

iTrader: (5)

Guys I am swapping the gears in my rear end and was looking at 3.73s but my local shop has a set of 3.90s in stock and they are the orangish boxed motives. What diiferences would there be on an A4? i was told it would only be like a 200 RPM difference.

alamantia

iTrader: (10)

thats a good ratio for an A4, do you have a PCM program to calibrate the speedo?

9formula4

iTrader: (5)

i have not bought these yet. Yes I am having my PCM tuned for the gear swap and the mods being added into the motor and such.

My question is.... How much of a difference will there be with the 3.90s from the 3.73s? I have seen a lot of talk on the 3.73s and wondered if it is a huge difference.

alamantia

iTrader: (10)

if you currently have 3.73's nothing noticeable, if you have 2.73's or 3.23 it will be a nice upgrade, 4.10's are probably a bit too much for an Auto

9formula4

iTrader: (5)

thats why I am asking about the 3.90s. Will they be overkill or no?

alamantia

iTrader: (10)

naaaaaaaa

9formula4

iTrader: (5)

alright cool then. I will go pick them up when they call me about my other parts being in. Thanks.

alamantia

iTrader: (10)

what series carrier do you have now? What series are the 3.90s?

9formula4

iTrader: (5)

I have a 2 series carrier but these are 3 series gears so i am picking up the spacer for them. They do not make motives in the 2 series in the 3.90 gear ratio. The spacer is 52 bux through summit so I am not worried about it.

alamantia

iTrader: (10)

exactly why i asked, you did your home work, nice!

9formula4

iTrader: (5)

yep I have been planning this swap for a while but I figured why not whil I had everything out of the car.

alamantia

iTrader: (10)

just ask if the spacer allows the ring gear to still be press fit (register) on the posi foir concentricity, otherwise, if teh ring gear isnt concentric on the carrier the spacer may be a bad idea

9formula4

iTrader: (5)

yeah.. it is a motive spacer but I will definately ask about it.

mzoomora

iTrader: (36)

The spacer itself isnt a press fit, and the ring gear on any that I have done is a tight fit but not a press fit. It SHOULD stay centered and I havent heard of anybody having excessive runout, pattern shift or vibration problems, but they arent a good idea for performance applications. You are using a longer bolt to hold together 3 pieces that are not a press fit instead of a shorter (stronger) bolt to hold together 2 press fit pieces. I have seen them used in light performance applications, but these cars are hard enough on the stock rears. Add in a shorter gear and a spacer and I think you are asking for trouble.

9formula4

iTrader: (5)

easy to say but noone has the 2 series 3.73s and the 3.90s don't some in a thick gear 2 series like the others. I am not paying 300+ for a set of rear gears, just ain't gonna happen.

mzoomora

iTrader: (36)

http://www.byunspeed.com/product_inf...d738cbd5ed0493

Have you called them? Both richmond and motive make them, there should be some in stock somewhere. Also, the extra cost now might be worth it if the spacer were to cause problems. How much more is it than the spacer and gears combined? If you are set on 3.90's that is a different story, then your only options are a spacer or new diff case.

alamantia

iTrader: (10)

I think what mzoomora is saying is that the spacer could cause problems which would wind up costing you more $ in the future. I believe he is just giving you options as a lot of gear companies make 3.73's for a 2 series even motive, i believe New Era has and Thunder carry them