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Thread: Allison 1000 5 speed gear ratios

  1. #1
    Join Date
    Oct 2007
    Location
    Westminster, MD
    Posts
    18

    Default Allison 1000 5 speed gear ratios

    What are the gear ratios for the 5 speed Allison 1000 transmission (used in 04 duramax). I can find info only on the newer 6 speed Allision 1000 here

    Thanks!
    2004 Chevy 2500 Ext. Cab Duramax LLY/Allison

  2. #2
    Join Date
    Apr 2001
    Posts
    275

    Default

    First five gears are the same, as nothing substantial changed in the planetary gear set. (IIRC, they changed the helix angle on the gears for noise reduction, but that has no effect on gear ratio.) Sixth gear is just an additional overdrive that could not be applied until they added the new solenoid to the valve body.

  3. #3
    Join Date
    Apr 2001
    Posts
    275

    Default

    Not necessarily. If the unit was built before June, 2003, it did not have modulated main pressure, and therefore does not have the main mod valve body or the G Solenoid. There is no way to get six speeds without that solenoid. If I remember correctly, GM incorporated that as a mid-year change in '04, so a 2004 truck could possibly either have the solenoid, or not have the solenoid, depending on the build date.

    Regardless, the answer to the original question is not affected. The gear ratios on ranges 1-5 did not change with the inclusion of the 6th range.

  4. #4
    Join Date
    Oct 2007
    Location
    Westminster, MD
    Posts
    18

    Default

    Ok, thanks!

    I am sure you all have seen the 6-speed conversion kit available for the 1000. Here is a link where it is briefly discussed. LINK

    Pretty expensive though.
    2004 Chevy 2500 Ext. Cab Duramax LLY/Allison

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