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maximum speed using 4 HI...

Discussion in 'The Garage' started by mudseeker, Feb 19, 2006.

  1. mudseeker

    mudseeker Registered Member

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    Greetings, noobie question here so i will make this as short as possible. What is the maximum speed you can operate at in 4 HI on say icy roads and such? I have heard conflicting answers this morning and need some info. Thanks in advance...
     
  2. roadnotca

    roadnotca 3/4 ton status

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    How fast do you want to go on ice?:haha:
    Edit; Why?
     
  3. jhellwig

    jhellwig 1/2 ton status

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    As fast as it can go till it explodes.



    I have run vehicals in 4hi going 70mph or so. The onle thing would be is that if you has front and backk sliping and something decided to grab. Then you could have a boo boo.


    Quite frankly though I find that a vehical is much more predictable on the slick in 2 wheel drive.
     
  4. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    My '85 owner's manual says "do not exceed 40 mph" in 4H.
     
  5. roadnotca

    roadnotca 3/4 ton status

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    Maybe the F Dshaft isn't balanced beyond that, or the ATF in the T-case starts foaming.:haha: We need some Trophy Truck peeps in here.
     
  6. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Misfire on my part! That 40 mph is for 4L, of course. There isn't any max listed for 4H. However, I wouldn't want to go much faster than 40 on an icy road in any case, not in something with a high CG. In an AWD car, sure, but not in my K5.
     
  7. Jishory

    Jishory 1/2 ton status

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    without driveline bind issues i would assume 70 mph is fine, blazers did come with full time t-cases for a while so highway speeds wouldnt be that bad... just dont turn too sharp
     
  8. 70jimmy

    70jimmy 3/4 ton status Premium Member GMOTM Winner

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    I would agree 70 won't hurt anything, other than maybe build up more heat. My 74 with full time I had going 70 in 4 high for several miles at a time.
    However the faster you go when you let off you are more likely to get (compression braking) or the slop in drivetrain and gears to cause you a problem.

    If you can go 70 in 4 high you ought to be able to go just fine in 2 wheel drive.
     
  9. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Remember the full time 203 cases.

    I would go as fast as I could in 4WD as long as lube levels were where they should be. (Edit: This is solely from a mechanical limit standpoint).

    I would not go fast on ice :doah:however in 2 or 4 wheel drive.

    Also manuvers in 4WD can be tough at higher speeds due to driveline bind (BE careful).

    Another thing to keep in mind, is that stopping is the same whether it be in 2 or 4 wheel drive. It's funny I see more 4WD's off into ditches in the winter than 2WD's. 4WD is a false sense of security.
     
  10. Blue85

    Blue85 Troll Premium Member

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    I've gone pretty fast with the hubs locked - probably 70mph. I think I've done that with the T-case in 2HI and 4HI. I sometimes shift in and out as I change to roads with and without good traction and just leave the front end spinning.

    The thing is, if you have good enough traction to be traveling at high speed, you have enough traction to bind the 4WD so it's really better to be in 2WD. if you want to go fast in 4, you need an NP203
     
  11. 79k20350

    79k20350 3/4 ton status

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    there is a big differance driving a full time truck at 70 and a part time! 203 have differentials in them so they alllow some slipping so they dont binds. last time i drove over 45 on hard pack i got binding in my drivetrain, does not sound good. i would not reccomend any type of speed on hard pack, even icy roads in 4wd
     
  12. 79k20350

    79k20350 3/4 ton status

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    This is not true, the stopping part anyways. you can stop better with 4 wheel drive, its calle dcompression or engine braking. yes alot of people get into accident i 4wd's but that is cause they dont know how to drive. 4wd definetly helps you stop!
     
  13. HarryH3

    HarryH3 1 ton status Author

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    I drove from Houston to Mobile a few years ago in 4HI on I-10. It was freakin' POURING rain and the highway was puddling up pretty good. The BFG All-Terrain 33's would get squirrely from time to time as they tried to find traction under the puddles. 4WD made the rig WAY more stable and it didn't dart around hardly at all after that. We were cruising about 65 MPH the whole way. :)
     
  14. wildmouse216

    wildmouse216 1/2 ton status

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    Let's see, maximum speed in 4lo is 40 mph with a nearly 2 to 1 ratio in np205 transfer case, so in 4hi should be 80 mph.
     
  15. atho

    atho 1/2 ton status

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    when my truck was driveable, in the winter i'd just lock the hubs in and select 2/4wd as necessary. sometimes i'd do upwards of 60-70 one way trip miles in 4hi, no problems.
     
  16. walla2k5

    walla2k5 1/2 ton status

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    Until you find the ditch....:D
     
  17. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Assuming all of the components are in good shape and you do not have any u-joint angle or inbalance issues, you can drive as fast as the road conditions dictate. As mentioned, if you really need 4wd than the roads will be at least somewhat slick and therefore the speeds will be lower.

    I've done a lot of long-term durability and evaluation testing for major auto manufacturers, and a lot of this testing includes driving part-time 4wd trucks locked in 4-high and 4-low for long periods of times while on dry asphalt and concrete surfaces at speeds approaching 100 mph.......I'm talking thousands or even tens-of-thousands of miles on lot's of different vehicles........and I rarely ever see a failure that can be contributed to running in 4wd on these surfaces.

    On my personal daily driver / towrig I've ran for over 100 miles continuous in 4-hi while pulling a 9,000 lb. trailer when the roads conditions were constantly changing......some areas were snow covered, some were icy, and some areas were clean dry asphalt.

    In general, 4wd does NOT help braking during the typical braking manuever on the road. Going down a hill in 4-low on the trail, sure it helps, but not on the road. The wheel brakes, again assuming in good shape and appropriate size, should have more than enough power to slow the wheels down...and be much quicker and more controllable than any normal compression braking.
     
  18. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Yes and No. Compression braking on high traction surfaces does help, but too much compression braking and all 4 wheels become ice-skates when in 4WD and on ice (= BAAAAAD). At least in 2WD the front brakes (which do most of the braking) aren't linked to the driveline and actually allow quicker stops and better steering on slick surfaces. On wet surfaces 4WD may be better but not on ice and snow for stopping....

    It also is a case by case basis depending on several variables.
     
  19. mudseeker

    mudseeker Registered Member

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    Thanks for all the info here. :bow: I drove to work this past Sunday in 4HI at around 45-60 in the ice and sludge. A friend of mine told me I would tear up the t-case doing that. I figured they called it 4HI for a reason,so use it. Hell if it breaks it needed replacing anyway right.:haha: I couldn't get the answers I wanted from the Chevy house so Idecided to go to the folks that would know. Thanks for the knowledge guys, Dennis.
     
  20. sledheadak

    sledheadak 1/2 ton status GMOTM Winner

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    i drive in 4 hi all the time in the winter when the roads have snow and ice on them.drive at speeds up to 75-80 mph and never have had a problem with the 4wd system.on my manual 4wd trucks i lock it in in oct with the 1st snow fall and dont take it out til the roads are clear again.if you have a non 4 wheel abs rig you wll stop a little sooner in 4wd since all 4 have to lock rather than just the front tires locking 1st.i have driven in snow since i was 16 and where i grew up it averaged 35 ft of snow in town.
     

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