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Thread: TC Locking on Diesel Trucks

  1. #1
    Tuner
    Join Date
    May 2008
    Location
    Texas
    Posts
    119

    TC Locking on Diesel Trucks

    I do not have a diesel, but I do have a (re: towing) question.

    Does anyone have a sample of their TCC table from a diesel?
    Basically, does a diesel have lower locking parameters than a
    gas engine due to its ability to make so much low end torque?

    Also, what does the "tow/haul" function change on a modern
    diesel truck equipped with automatic? I assume maybe shift
    speed, pressure and/or points, but I'm curious if it also lowers
    the locking speed (to lessen heat) and/or stop you from using
    overdrive?

    I have heard from many people who tow in OD with a diesel,
    while others say never tow in OD. I assume cruising with the
    TC unlocked is a major source of heat generation, thus I was
    curious how diesels handle locking TCs vs gas.

    Thanks!

  2. #2
    T/H mode indeed locks the TC earlier... around 18mph in 2nd gear (higher if your hotter on the throttle but still pretty low). They will stay locked under WOT through every gear after that as well (the Allison will shift while locked up)

    I modified my non t/h tables to still lock up by 22ish mph IIRC. Under light throttle this was just after shifting to 3rd. From the factory they don't lock them until 50+ again IIRC. And t/h mode has to reach higher rpms before shifting which can be annoying for light throttle easy accel.... this combo works out great for normal driving! Doing this did knock heat down noticeably as well.

    They finally took the right approach to this IMO... you can now pull a heavy load in the lower gears (also low airflow across cooler) with whatever pedal position required without having the lockup release... makes sense!

    I would post my modified tables but I am not on my tuning laptop currently.
    06 LBZ DMax / 6spd Allison 4x4 ACSB - Self built/tuned sideways s366 setup | DPC converter / Co-Pilot | Holley HP150 / BD Filter setup | hood stack | Homebuilt IC pipes | Homebuilt Trac Bars | Black951's | Coolingmist stg1 | ISSpro | PPE | self lowered 3/5 | Roll Pan 12.6@105 5800ft (stock trans)
    02 WRX w/ STi 6spd - Self built/tuned Holset setup w/ a buttload of other goodies 11.75@119mph 4800ft (stock block) Built Motor finished!
    TJI Tuning

  3. #3
    Potential Tuner
    Join Date
    Aug 2010
    Location
    PA
    Posts
    4
    I agree with the general. By the way, BADASS Sti.
    2005 GMC Sierra 3500 4x4 SLT
    Suncoast built tranny and TQ converter
    Green Intake, AFE 4" Turbo back (shortened to side exit)
    Res removed, PCV re-routed, EGR blocked
    Autometer C2 Boost & Pyro
    Self tuned 389 HP & 752 TQ