Max. Speed in 4wd?

Discussion in 'GM 6.5 Diesel Engines' started by toddlnrd, Jan 21, 2009.

  1. toddlnrd

    toddlnrd My first diesel!

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    My Suburban has three separate 4 wheel drive settings. What is the max recommended speed in the 4wd auto setting? What about 4-Hi? (I realize that I do not want to use 4-Hi unless I am on lose gravel or snow, definitely not pavement.)

    We just had 6-inches of snow yesterday. The primary roads are clear but the secondary roads are not.

    Thanks,
    Todd
     
  2. DEERE3594

    DEERE3594 I welcome everyone...not just Penguins!

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    I have used 4H as fast as interstate speeds. 4L just for pulling out stuck stuff and doing tug-o-war. I dont have the auto setting on mine.
     
  3. chrisk1500

    chrisk1500 New Member

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    4 HI at any speed anywhere with questionable traction (rain, ice, snow).....but that's just me - without a rear locker this truck has no traction unless in 4 HI....
     
  4. mattthebrat

    mattthebrat Diesel Dork

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    Auto 4 and 4 high are both all speed, I don't know about you, but if it were me I would rip out that auto 4x4, might be good for racing though.
     
  5. toddlnrd

    toddlnrd My first diesel!

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    just found the owners manual. 4wd auto is for mixed driving conditions (any speed), 4-hi is for severe conditions (any speed), of course 4-lo is for pulling stumps and Fords out of ditches.

    Todd
     
  6. jmiller

    jmiller Recruit

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    I've run 4x4 Hi at any speed, any conditions. Dry roads, +80 mph, etc. I put 100k on the toyota 4x4 system. One too many 4x4 hole shots and 4x4 power slides, broke both pinions after 180K. Retired after 250k.

    Lo generaly max's about 40mph or so.


    Generally, 4x4 shoud be used for off highway, or low traction situations.

    If your tire pressures are equal, Tire wear is even, you don't romp on it all the time; you should be fine.

    The 4x4 power slides are kind of cool though. especially in a 7000lb truck.
     
  7. Michaeljp86

    Michaeljp86 EVIL GENIUS

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    Auto 4x4 will keep it in 2wd unless the wheel speed sensors shows your losing traction. It keeps the front diff locked so mpg goes down a little and just engages the transfer case if you loose traction.
     
  8. JeffsJeep04

    JeffsJeep04 New Member

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    Yup, when it's mixed snow/dry road, I sometimes just leave it in 4x4. The auto position my last truck had could be a little inconsistent. By the time it locked in, it'd generally be too late. As long as you aren't turning, the bind on the driveline is very minimal, even on dry road unless your tires aren't inflated properly. If you have dry roads more then 1/4 mile or so, then go ahead and use 2x4 or auto. I don't miss that auto position one bit though, lots of jerking and such...I know when it's going to be slick and can just pop it in 4x4 before I need it and save a lot of fooling around.
     
  9. Matt Bachand

    Matt Bachand Depends on the 6.5

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    I dont' have auto, i have the real lever on the floor, but have drievn them. They stink, you take off, rear tires spin a little, then it slams in the front. Not good.

    4x4 use it if you have it, key is, BEFORE you need it.
     
  10. Michaeljp86

    Michaeljp86 EVIL GENIUS

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    My moms 04 yukon has auto 4wd and it works nice, its a nittle slow but works great. The 98 tahoe had it to and it was like matt said, you would spin and then it would lock up. The yukon works way better, I think its made for idiots who dont know how to drive. I drive my jimmy all over and never been stuck and rarely use 4wd. If you know how to drive you dont need auto but Im sure you guys know most people dont have a clue how to drive.
     
  11. RayMich

    RayMich New Member

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    I have driven in 4-Hi at 70-75 with no adverse effect other than worse fuel economy.

    My truck doesn't have Auto-4WD.

    I had Auto-4WD in my '02 Trailblazer and I did NOT like it at all. The truck drives in 2WD until the wheel speed sensor senses that the rear wheels have lost traction and then you can feel the 4WD kick-in. It is not very smooth at all and you still pay the fuel economy penalty because the front differential is engaged all the time.

    As far as that is concerned, nothing can beat All Wheel Drive (AWD), where you have a center differential and all 4 wheels are pulling all the same time. I had AWD and G80 rear locker in my 1977 Suburban and my 1979 K-10 Chevy truck and I loved it. It is great when you find yourself on slick ice in the middle of a turn. You can't even feel the differentials biasing the power. Some people did not like the 2 mpg fuel economy penalty from running in 4WD all the time, but to me the added safety is worth it. I wish we could get AWD in our trucks.
     
  12. packratt

    packratt Member

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    Figure out how to replace that leaky transfer case of yours with an unmodded NP203.
     
  13. jrsavoie

    jrsavoie Recruit

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    I don't think you should ever use auto. It is hard on the encoder motor & cuts their life by big percentage points because it is constaqntly shifting in & out of 4 wheel drive
     
  14. Harqobispal

    Harqobispal LIVE FREE or DIE HARD

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    I once accidentally drove to work, on the completely snow free , freeway, in 4wd. 75-80mph. Couldnt figure out why the truck was handling so wierd. When i pulled into the work parking lot, i could smell delco tranny fluid burning. I looked down, and the lever was in 4-hi. Of course i immediately shifted it out of 4 hi. Shut the truck off, and got out, to go into work, you could hear and smell the burning. The transfer case was cooking, very hot. This was on a K2500 with manual 4x4 lever. I just remember an old guy saying "Never drive in 4x4 on dry pavement". I think this is true even on the new trucks. Am i wrong in saying that the front wheels pull harder than the back ones? SO the whole time you are driving on dry pavement you are heating everything up?
     
  15. JeffsJeep04

    JeffsJeep04 New Member

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    Yes. When in 4x4, you are connecting the front and rear axle directly, they both receive 100% power. No bias. When you make a turn, the front travels further then the rear, that's where the strain comes from.
     
  16. malibu795

    malibu795 misspleelleer..........

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    i go that NP203 in my 75 K20 and a clutch locker in my 14b out back and opne diff up fornt..... love it


    NVG make as AWD t-case that went behind the allison on the H1 Alphas.. its 2700 bucks form the hummer/cad dealer
     
  17. JeffsJeep04

    JeffsJeep04 New Member

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    I wouldn't run it in a HD truck though. The hummer had geared hubs which allow much less strain on the drivetrain. The NVG case is the 242, same as comes in the jeep liberties and cherokees. Great T-case, but not nearly strong enough to handle the loads our trucks would put on it.
     
  18. Missy Good Wench

    Missy Good Wench Wild Blonde from Cloud Mt

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    The big issue with the electric (auto 4x4) is the fact that the system is all controlled with electronics.
    If the electrical system has an issue, your fouled.

    The auto 4x4 systems use a magnetic clutch in the T case and yessss they are capable of slamming in when the computer senses a preset speed difference between front and back wheels.

    I dont even like the electric lockup on the front end let alone the electric T case.

    4x4 is manual hubs, and a lever on the floor that shifts the case.

    When I want 4x4 its because I need the rig to get me home or ??? and I dont have any patience with some electronic POS in charge of running the show for me.

    Nuff said.

    The Old NP 203 full time cases were great. Easy to use and very reliable. Most casual driving on dry roads right on through even minor snow or mud and the Full time position got the job done.
    Tough spots required the lock function to be used.

    MGW
     
  19. Matt Bachand

    Matt Bachand Depends on the 6.5

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    Why doesn't this get lost in the front differential as on a 2wd car? becaue the rear tires are always pushing? I guess I don't understand why the front Diff doesn't compensate.
     
  20. Michaeljp86

    Michaeljp86 EVIL GENIUS

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    I think you would need some sort of clutch to let any binding loose. On my dads JD if you run it down the road in 4wd you can see the wear on the front tires real quick.
     

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