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Does anybody know how the power is split up between the front and rear?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by PetaKane, Dec 13, 2002.

  1. PetaKane

    PetaKane 1/2 ton status

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    Is there a chart or something online that shows the difference of power to the wheels when in 4 high and in 4 low? Something that I've always wondered about.
     
  2. azblazor

    azblazor 1/2 ton status Premium Member

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    With a common "part-time" type 4 wheel drive system, in 4WD either hi or lo - the front and rear drive shafts are essentially locked together through the transfer case. In the "full-time" (i.e. NP203) system, the transfer case actually has a differential in it to allow the front and rear driveshafts to turn at different speeds ( just like an axle differential) UNLESS it is in "lock" position (or has been converted to "part-time.)
     
  3. PetaKane

    PetaKane 1/2 ton status

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    Okay, that makes sense. But here's where I get confused..when I'm in 4 high and I'm in mud, the front tires aren't spinning nearly as fast as the rears. In 4 low it looks like they are spinning about the same as the rears. How does that work?
     
  4. milspecjimmy

    milspecjimmy 1/2 ton status

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    do you have the same gear ration in both axles?
    /forums/images/graemlins/usaflag.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif
     
  5. PetaKane

    PetaKane 1/2 ton status

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    Yep, 5.13's all around
     
  6. txbartman

    txbartman 1/2 ton status

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    Then you have a problem. Are you sure it isn't just visual perception? If your tires turned at different rates, then you would not be able to drive and any solid surface without SERIOUS problems. Would be like running different gear ratios in the two axles.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    put it 4wd in a straight line on the street and roll. It should roll in a straight line no problem. If it doesnt want to roll then one of those axles don't have the same gears as the other.
    Out of the transfer case it will spin both drive shafts at the same speed PERIOD.
    Only case that might have times that it wouldn't spin the shafts at the same speed is a NP203 that is still full time.
     
  8. Thumper

    Thumper 1/2 ton status

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    Good question... but to add to it, I have heard some say that there isnt as much torque sent to the front driveshaft as the rear. If the shafts are basically hooked together in the t-case, how can the torque be split any other way than 1/2-1/2?
    Mike
     
  9. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    On what case? on 205,208 and 241 in 4wd it will drive both drive shafts at the same speed. There is no clutch type device in any of those cases. It's all mechanical and either it's in 4wd or not.
    Now a NP203 that is still full time and not in LOC you could loose traction on one front wheel and ALL the power go to that wheel. Once you shift the 203 into LOC then it will run both drive shafts are the same speed.
    Probably what happend is the front axle is open. He's hanging out the window looking at the tires and the passenger side was spinning like mad and the driverside wasn't .
     
  10. Z3PR

    Z3PR Banned

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    I've got the NP-203 still fulltime. I'm planning on installing a Detroit Locker in the 14 Bolt FF rear. Have Dana 44 up front. Wasn't planning on a locker for it, but is there a way to make it grip instead of slip ???? Yes, I know about shifting into high or low lock, but wasn't talking bout that.
     
  11. txbartman

    txbartman 1/2 ton status

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    The idea of power being split differently between the front and the rear is a myth. The laws of physics require the torque to be split 50/50 between front and rear. Only things that may make it feel differently are the weight transfer and so forth.
     
  12. azblazor

    azblazor 1/2 ton status Premium Member

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    The best way to get "grip" in the front, would be to put a limited slip in the front. I have a power-lok in my D60 and like it very much. A lot of people on the list have a lot of experience with different types of limited slips and lockers in the front. Much info has been posted Or you could post asking for info /experiences on a specific type that interests you.
     
  13. jjlaughner

    jjlaughner 3/4 ton status

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    I thought I heard somewhere that the transfercase was like a 60 rear: 40 front split? I'm not real sure. I know on ice and snow I can kick the back end of my 87 blazer round the front with the front tires kickin up snow. It makes people give you fully looks when the front tires are driving straight and rearend is turned 15-20 degrees to the side and you are going straight down the road! That tells me that the rear has more power/rotation than the front. I dont mess with 4lo low much in the snow, I drive to fast /forums/images/graemlins/thumb.gif so I dont know the difference in feeling on the 4hi/lo situation. /forums/images/graemlins/smirk.gif

    Yes the gearing is the same front rear, factory 3.08 (for the time being). I put an aulburn limit slip in the rear after I ate 3 gov-locks in one winter. Most of the time I'm on the highway running 55-60, but we play offroad a little too /forums/images/graemlins/deal.gif
     
  14. Triaged

    Triaged 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    The idea of power being split differently between the front and the rear is a myth. The laws of physics require the torque to be split 50/50 between front and rear. Only things that may make it feel differently are the weight transfer and so forth.


    [/ QUOTE ]
    Torque does not have to be split 50:50 if you have a 203. The way you could get a different ammout of torque to one axle is to runn different gears front and rear (like 3.08 front and 4.10 rear). The diff in the t-case puts out a 50:50 torque split. The extra reduction in the rear at the diff would put more torque to that axle. This example would be 43:57 (front:rear). The only problem is that the 203 isn't designed for that constant difference in rotational speed of the front and rear driveshafts and will burn up.

    With a 203 in loc (or any other locking t-case) the toruqe split isn't exactly 50:50...it is the rotation speeds of the driveshafts that are the same. It all depends on available traction and how close the diff gears match. If traction was high enough you could even have negative torque on one axle!
     
  15. 95 Silverado

    95 Silverado 1/2 ton status

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    If you have a posi or locker in the rear it will keep both rear tires spinning the same speed, an open front will allow the front wheels to spin at different speeds, the spinning wheel going the fastest, the single spinning front wheel will be going faster than the rear wheels, lock the front wheels together and they will all spin at the same speed.
     
  16. DieselDan

    DieselDan 1/2 ton status

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    Keep in mind also even in 4-LOC with open diffs front and rear you are going to see different wheel speeds. When a one side wheel stops turning the opposite side will be turning twice the effective normal speed (2 x gear ratio)
     
  17. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Unless of course you add a viscous clutch in the t-case, then you can adjust the case for different front/rear outputs. (Like the early 90's AWD Astro/Bravada/Typhoon, they just had a 241 with a clutch inside) None of our trucks have that in Lok mode. A differential is different than a clutch, the differential just allows the shafts to spin a different speeds.
    The clutches actually reduce or make the output "heavier" on one shaft, therfor the power will go to the other.
    Of course the better way to do it is to electronically control it, like an Audi t-case does, although I don't know of any adaptors for and Audi A8 case to an SM465 trans....

    BlazerMan
     
  18. Thumper

    Thumper 1/2 ton status

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    K, sure there are a lot of variables... but... in a truck, with 4:56s front and rear, a 205 tcase that is stock, why do people say that the front doesnt get as much torque as the rear. For example, I was told that using a front CV type shaft on the rear wouldnt be good because the tubing is too small, and the rear gets more torque than the front, so the shaft wouldnt take it. I just dont get the fact that if the output shaft speed is the same, the diff gears are the same, what can possibly cause more torque to go to the rear? I dont know about anyone else, but my truck is hella hard to get into a 4wd donut on ice because the tires are all spinning at the same speed. I can do it, but its takes some finesse. Now wouldnt it be easier if the rears were faster?

    So... this all being said, why is the front shaft on almost every vehicle way smaller than the rear? Is it a space issue? Or a long term reliability issue? Or maybe its just physics. The weight transfer of the vehicle when the power is being applied makes it nearly impossible to break even a small front shaft because the front tires lose so much ground pressure? So, the rear shaft is made to be able to handle anything the motor can throw at it, and the front is designed so that it can handle as much as it needs to?
    Beats me... /forums/images/graemlins/confused.gif
    But it would make sense why the front shaft is not going to be able to take the strain on the back. Not because the tcase puts out more to the rear, but physics makes it that way. Right? /forums/images/graemlins/grin.gif

    /forums/images/graemlins/k5.gif

    Mike
     
  19. m j

    m j 1/2 ton status

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    front shaft is in use only a very small % of the time
    front would see more torque in my opinion due to the weight over the front,
    tho tRusty states his k5 is near equal weight bias it isnt so in my truck
     
  20. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Depends on the case. If you're talking about your 87's 208 then no it is a 50/50 power out split.
     

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