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How to tell rear gear ratio?

This is a discussion on How to tell rear gear ratio? within the Drivetrain forums, part of the LSx Technical Help Section category; Hi all, My dad has a '99 SS. It's a reconstructed total ( ) so we don't know the ...

  1. #1
    Member turbojimmy's Avatar
    Join Date
    Feb 2007

    2002 Trans Am Convertible

    How to tell rear gear ratio?

    Hi all,

    My dad has a '99 SS. It's a reconstructed total ( so we don't know the history of the car. We do know that at the very least it has an aftermarket exhasut. It also felt quicker than my brother's '02 WS6 TA and tweaked '99 Z28 which makes me suspect it has gear in it. It performs pretty close to stock at the track, however.

    He's had the car for about 6 years and it's always had a very loud growl in the rear. After reading a lot of the complaints on the 'net he insists that it's 'normal'. I drove the car to work and back 3 days this week and just can't believe that GM would let something leave the factory with this kind of noise. It's deafening. You can't carry on a conversation in the car without yelling and you can't hear the radio or even the aftermarket exhaust over it. Dad says it's because there's very little sound deadening material. I don't think so.

    When you go around corners it changes tone (gets deeper) and I swear I can feel every tooth on the pinion meshing with the ring gear at low speeds with my hand on the shifter. It's definitely coming from the carrier - it's not an axle bearing or anything.

    Anyway, long story short I think the previous owner put gears in it but didn't do it correctly. Either that or something got messed up in the accident (neither axle is bent tho). It's lasted 6 years like this so I'm wondering what to look for if I pull the cover off of it. It should be pretty obvious by this time if the gears weren't meshing properly. If I spin the wheels and count the driveshaft rotation that should tell me the ratio, but can I tell the difference visually between the stock 3.42 and, say, 3.90 gears?


  2. #2
    Senior Member
    Join Date
    Jul 2005
    Jacksonville, FL
    You can play with a RPM/MPH gear calculator like Probably should pull the cover anyway if it's making all that noise - with it off just count the teeth and do the math. Ex: 42 tooth ring gear/13 tooth pinion gear - 42/13=3.23.
    Last edited by 2001NBMZ28; 08-03-2007 at 11:28 AM.

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