Explanation of 4 hi vs 4 lo

Discussion in 'GM Powertrain' started by jbeall, Dec 21, 2009.

  1. jbeall

    jbeall Rockstar 100 Posts

    Hi All,

    I've got a 2003 GMC Yukon XL. I use the 4 hi setting when I'm in icy or snowy conditions and the pavement hasn't been cleared, or I'm on gravel, etc.

    I've read the manual's description of what 4 lo is for ("delivers maximum torque to all four wheels"), but I'm still not clear on what it actually does. It is just a gear reduction that lowers the ration of engine revolutions to wheel revolutions, thus giving slower speeds with higher torque? Or is it more than that, e.g., is it locking the differentials to prevent wheel slippage? In which case you would only not want to use it on pavement, only in snow, ice, mud, or other conditions where the wheels can slip as you're going around a turn.

    I've been searching on this and have found some general info on what 4 hi vs 4 lo can mean, but nothing specific to my vehicle--and it seems that the meaning can vary from vehicle to vehicle.

    Thanks for any feedback!

  2. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    its just lower gearing. i wouldnt even mess with the 4lo, there are alot of people that use it wrong, and there alot of threads on hear with people that have screwed things up using it. RARELY dose the average person get in a situation that should 4lo be used.

    DAREDEVIL Rockstar 4 Years 1000 Posts

    As far as i know ,,the 4 low also locks the diffrential ?! for better traction ?!
    U should definatley not turn in 4 low, makes funny klunk noises if u do !
  4. azdrtdog

    azdrtdog Epic Member 5+ Years 100 Posts

    The 4 lo is for situations where the engine might not have enough grunt to power the wheels with authority like deep soft sand or loamy earth that swallows the tire but still gives traction.the clunk noise is usually common as it shifts it sounds through the drive shafts as it engages from a neutral position and meshes the cogs, noise while operating could be internal issues but i've found the majority of them to be front u joints or cv's
  5. bigburb

    bigburb Rockstar ROTM Winner 100 Posts

    My understanding, 4lo helps deliver the most torque and traction to the ground. From my experience, 4lo is only good for about 35mph in OD/4th gear (only a one time thing, just had to see lol). It's very low geared. I only use it when I'm trying to pull someone out from being stuck and need all the power I can get, or when I'm off-roading up in the mountains and just want to creep along. But generally, I tend to avoid using it if I can. It just seems harder on the drive-train to engage IMO, and I usually don't need that much power to the ground anyway.
  6. cowboyjarman

    cowboyjarman Rockstar

    i live in 4 lo. all the trails i do you want the lowest gears possible. in four lo im about 52.6 crawl ratio. i dont have to use the brakes going down hill and uphill i dont use as much throttle. after i put dual t-case and 5.60 gears i should be arond 250 to 1 crawl ratio. it will make obsticles easier to climb with no effert from my motor. i love 4 wheelin.
  7. redneckarmyMP

    redneckarmyMP Epic Member 5+ Years 500 Posts

    im the exact same way.4 low is my best friend when on the trails.it makes a world of difference and helps alot
  8. cowboyjarman

    cowboyjarman Rockstar

    example of super 4lo. this truck is going .84 mph at 5000 rmp. its running triple t-case and its low is around 1200 to 1. www.marlincrawler.com . or look up marlin crawler on youtube and see it in action . hes in 5th gear and the truck go so slow that he walks away from the truck while its driving by its self. truly amazing stuff.
    Last edited: Dec 22, 2009
  9. bigburb

    bigburb Rockstar ROTM Winner 100 Posts

    Ah man... you're makin' me miss my old 'burban lol. I used to wheel that thing in the rockies all the time. 4lo was useful for that kinda stuff that's for sure.
  10. jbeall

    jbeall Rockstar 100 Posts

    Anyone confident that it does/does not lock the diffs?

    Anybody have a definitive reference (or is just really confident) that it does/does not lock the diffs when you go into 4-lo?

    I've gotten conflicting information about this. Some people say it doesn't lock the diffs, some people say it does. Wikipedia seems to think it does, because it mentions the Suburban as being one of the vehicles with "no center differential ... [and so] may not be driven in 4WD mode on dry pavement, or damage to the transfer case may occur." I assume it is implying that the 4WD drive mode (either 4 hi, 4 lo, or both) is a part time 4WD and will result in driveline bind if you try and drive it on dry pavement or another hi traction surface.

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