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Rearend Gears

This is a discussion on Rearend Gears within the Drivetrain forums, part of the LSx Technical Help Section category; I have a basically stock 99 T/A. Auto 4spd. Bought it new in 99. Added a magnaflow exhaust and a ...

  1. #1
    Junior Member havnaparty's Avatar
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    Rearend Gears

    I have a basically stock 99 T/A. Auto 4spd. Bought it new in 99.
    Added a magnaflow exhaust and a Ram Air hood with air box,3.73 gears.
    My question is this. I really don't have the cash to stick in the motor right now.
    Other than bad fuel mileage,what would the cons be to put in some 4.10 gears to get this thing off the line a little quicker. This is an everyday car other than winter months. Will there be much difference or worth it changing the gears?
    Thanks.

  2. #2
    None Shall Pass Knight's Avatar
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    Top speed will drop, rpms will be higher when crusing at higher speeds. Tach and speedo will read different too without an adjustment tune. Most people are of the opinion that 3.73s are the best gear for an a4. You might see a slight pickup in your 1/4 mile et - maybe .05 to .1 or so. If you're running a stock stall - IMO you'd be better off putting a better stall and maybe a shift kit + tune instead. Your call though.

  3. #3
    Exalted Cyclops 67CamaroRSSS's Avatar
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    Big stall (3400 or bigger) will put a smile on your face. You'll need supporting mods also like a tranny cooler and tuning. While it's out you might want to take a look at the tranny internals.

    If you do gears 3.73 is better than 4.10 for an A4 because we only have 1 overdrive gear.

  4. #4
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    I gained .5 in the 1/4 going from 3.23s' to 4.56s',going from 3.73s' to 4.10s' you might gain .1-.15. Do a stall w/fluid cooler,as you already have the ideal gear(3.73) for an A4.
    MPG is right foot dependent,I only lost 3mpg with the 4.56s'.

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    Senior Member tatertot91's Avatar
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    Quote Originally Posted by 67CamaroRSSS View Post
    Big stall (3400 or bigger) will put a smile on your face. You'll need supporting mods also like a tranny cooler and tuning. While it's out you might want to take a look at the tranny internals.

    If you do gears 3.73 is better than 4.10 for an A4 because we only have 1 overdrive gear.
    +1 agree with all the above

  6. #6
    Auto Painter RyanJM's Avatar
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    I have an A4 with 3.73's and it's only a weekend toy and I wouldn't go up to a 4.10 unless I was just driving it to the track and meets. With the 3.73's it's at 2500rpm and we do alot of highway driving and even the backroads are 65 to 70mph an usually going faster so my car is always at 3k rpm so I couldn't see 4.10's if you drive it alot.
    1998 Trans Am 85k miles.
    Bolt ons, MS3 113LSA cam, Circle D Stall, Tune, Modified WS6 style hood, Full Suspension, 6000k HID's, Clear Side Markers w/ Leds, Led 3rd Brake Light and 18" AR Staggered Killer Wheels w/ BFG KDW NT's.- Weekend Toy/DD
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  7. #7
    Retired NOT tired SteveC's Avatar
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    one of the "cons" of 4.10 gears in an A4, would be highway driving. Just say you were doing 70 MPH in O.D., and you need to pass (go around another vehicle), so you give it more gas, and the PCM decides to drop it into 2nd gear, you are now way over the redline, and you can blow the engine.

    I have 3.73's and a Y3000 yank stall, and I go from "farfegnugen to fukenmovin".

    Get a 3600 stall, and forget the 4.10's

    SteveC

  8. #8
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    I have 4.56s' in an A4,the PCM does not/will not drop it into an inappropiate for passing.

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    Moderator Cutlass's Avatar
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    Quote Originally Posted by oldmanZ28 View Post
    I have 4.56s' in an A4,the PCM does not/will not drop it into an inappropiate for passing.
    Very true.

  10. #10
    Senior Member karpetcm's Avatar
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    Ive never heard a PCM dropping it in a wrong gear just because you've moved up to 4.10's in a A4. This could be something i wasnt aware of but ive never heard of it nor thought it was possible.

  11. #11
    Veteran Hi-Po's Avatar
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    4.10's in the auto would be brutal! In a good way! Top speed obviously and a higher cruising RPM would be affected. Plenty have done it Just have to play around with gear calculators to see if it would be for you.

    It would definitely put some kick in.

    I would do a stall way before going to a higher numerical gear though.
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  12. #12
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    my 4.56s' with my 2800 stall(1000 over stock) is brutal in 1st and 2nd.

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