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Overdrive on off switch

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by senorschmidt, Jun 9, 2012.

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  1. senorschmidt

    senorschmidt New Member

    So, I have a 96 1500 burb and I want to put a OD on off switch to make it better for towing. Right now I can only really tow in third. There is no way I could tow in OD now, so the switch would be necessary. Any ideas. I looked unsuccessfully for some kind of aftermarket part with no luck. Thanks.
  2. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    Without looking it up, I'm assuming you have a 4 speed auto trans (4L60E).

    Why not just select D3 and let the trans shift no higher than 3rd gear.
  3. senorschmidt

    senorschmidt New Member

    6MPG is why.
    I would be stoked if I could find some way to get it up to 10 or so. I can't seem to find a tune for it (5.7L vortec, 4l60e, cold air intake, dual exhaust).
    I am towing a 4-4500 lb trailer, and my burb is needing anything help it can get. It tows fine in 3, but it just gets really thirsty!
  4. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    Hmmm, using a switch, or using the gear selector provides the same function. 4th gear is overdrive, 3rd gear is the 1:1 non-overdrive gear.
  5. senorschmidt

    senorschmidt New Member

    I guess my confusion was that when you are in overdrive it seems/feels like it switches back and forth between two different gear ratios, neither being third, and when it does this it heats up the torque converter really fast. I think I read somewhere that the overdrive on off switch seen in newer trucks just changes the rpms at which the truck would shift.
    When in overdrive it fluctuates between 1600 and 1900 rpm and then when I downshift into 3rd it jumps up to 2300. I want to keep it 1900 instead of it jumping back and forth between 16 and 19. Does that make any sense? :confused:
  6. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    Ok, I see your confusion. Overdrive (4th gear) is usually 0.70:1, where 3rd gear is usually 1:1. If 3rd gear lets the engine rev to 2300 (for your given road speed), then 4th gear should produce an engine speed of around 16000 (70% of 2300).

    So, 1600 seems to be the rpms you should see in 4th gear.

    You did not say what road speed you were traveling when you observed the above rpms, but I expect somewhere around 60 mph.

    A '96 'burb was not designed for economy, so it probably has a 3.42, or 3.73 rear gear set, which would produce 2300 in 3rd around 60mph.

    The tranny is in 3rd gear when both shift solenoids are in the off position, 4th gear shift is achieved when the 1-2 gear shift solenoid is operated while the 2-3 solenoid is off.

    I'm thinking, that you may have slippage in the 1-2 solenoid, allowing the revs to climb to 1900 and the tranny to heat.

    I think, that 1600 and 2300 are the revs you should be seeing and that 1900 is not a good thing.
  7. Ape

    Ape New Member 100 Posts

    Could it be a lock out switch for the torque converter that you're looking for? Not sure if it would work for a 4L60 or not? But I know muscle car and hot rodders that use 700R4's use converter lock out switches.
  8. senorschmidt

    senorschmidt New Member

    That might just be it. Now to figure out if it would work on a 4l60e.
  9. Ape

    Ape New Member 100 Posts

  10. RayVoy

    RayVoy Active Member 1000 Posts 100 Posts

    The converter lock up was invented to remove slippage in the drive train. When the converter is "locked" the engine crank and the rear wheels are mechanically connected.


    Without the lockup, the engine revs and uses a lot more gas, your road speed rpms could be 3000.


    Some GM trucks have a trailer tow mode switch. When the driver turns this on, the PCM changes the engine speed at which the transmission shifts. It keeps the transmission in a lower gear longer (until the engine reaches a higher rpm) before shifting. This maybe what you are thinking about. The PCM controls this, I do not know how difficult/easy it is to retro-fit.
    Last edited: Jun 11, 2012

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