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GTO or Trans Am Transmission Selection--MY FIRST POST!

This is a discussion on GTO or Trans Am Transmission Selection--MY FIRST POST! within the Drivetrain forums, part of the LSx Technical Help Section category; All- I have a '98 Silver Trans Am LS1 with a M6. I recently hit 160K. Current mods consist of ...

  1. #1
    Junior Member
    Join Date
    Apr 2008
    Kennesaw, GA

    1998 Trans Am

    GTO or Trans Am Transmission Selection--MY FIRST POST!

    I have a '98 Silver Trans Am LS1 with a M6. I recently hit 160K. Current mods consist of Volant CAI, Raptor functional hood, Edelbrock strut tower brace, Edelbrock LCA's, EBC rotors and yellow stuff pads, Corvette wheels all around, flowmaster exhaust (ya, need to upgrade), 3.73 rear end, and thats it for now. It's my daily driver and something i intend on building up over time. Mostly for street.

    The other weekend my transmission blew while on the highway. I had noticed some grinding going into 4th about a week prior. I was told the synchros were going out. While driving, i heard and felt something go. Almost like a flat tire. I pulled over and checked my tires. All were ok and knew my trans gave out. As i limped my car the next 6 miles off the highway to the nearest exit, my car sounded as if there was a freight train applying its brakes on the railroad with all the grinding. I could not go above 1500 RPM without violent shakes. Its been towed back and ive been on TDY. I noticed fluid sprayed all down the exhaust and drivetrain tunnel area. I have yet to pull my trans to inspect for the type of damage. Depending if the casing is damaged beyond trans rebuild, i want to know which route to go.

    I have heard alot about the GTO transmissions being stronger built and better gear ratios for acceleration. I have found one that came out of a '06 GTO that had a LS2.

    1. If i go this route, can i pull the bellhousing off my current trans and use it with the GTO transmission?
    2. Or is it a different transmission to bellhousing bolt pattern?
    3. Anyone know the PN for the quick release tool for the hydraulic clutch line?
    4. Will i need a LS1 T56 tail shaft to put on the GTO trans? If so, will my current one work?
    5. What is a recommended clutch slave clyinder and throwout bearing?
    6. Have i forgotten anything?

    Upon the swap, ill be upgrading to the GM LS7 clutch kit and going a different route with the clutch slave cylinder other than the OEM GM piece. I look forward to any responses and help everyone provides.

  2. #2
    Super Moderator
    pajeff02's Avatar
    Join Date
    Feb 2009
    Mansfield, PA

    Black & Blue
    '02 WS.6 / '07 Suburban

    Welcome to the site!

    Going to move this to the appropriate section of the forum for you.

  3. #3
    Join Date
    Jan 2006
    Jamestown, NC

    99 Z28

    Well I cant answer all those questions, but if the tranny can be rebuilt, I would highly suggest building it up and upgrading it instead of putting another stock piece in (if you plan on more mods) and I would also suggest getting the tick performance adj slave cyl to go along with your ls7 clutch.

  4. #4
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    I don't care much for the GTO box and there are a couple reasons why...

    Here are your gear ratios..

    GTO Fbody
    2.97 2.66
    2.07 1.78
    1.43 1.30
    1.00 1.00
    .84 .74
    .57 .50

    As you can see you lose some of the overdrive advantage (although slim) but even more important is that steep first gear. That makes the trans weaker from a numerical or mechanical standpoint, also makes the car harder to launch if traction is limited. You really don't need that much gear multipication in a lighter Fbody if you are running the proper rearend gearing.
    Another gripe I have is the GTO trans is not a close ratio box like the Fbody. The gear spread is much further apart so you have more rpm to recover with each shift. Okay for a torquey engine but not so much for a smaller high strung engine.

    I haven't torn apart a T56 from a GTO personally, but I would guess the upgrades that you mention are probably sincros and shift forks (those are T56 weak links) that GM possibly improved upon.
    I'd take Scott's advice and stick with your current T56 and upgrade what you have. A good rebuild kit with brass parts (instead of plastic) like your fork pads, better sincros for smoother high rpm shifts, better forks,'s all available.

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