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2.56's gear ratio???

Discussion in 'The Garage' started by 81sb, Mar 19, 2004.

  1. 81sb

    81sb Registered Member

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    2.56\'s gear ratio???

    Well tonight i pulled my diff cover to install my lockright and two things happened 1) I had a broken pinion lock bolt that I have to deal with and 2)I come up with a 2.56 ratio for my R&P. (41/16). I assumed I had an absurdly low ratio in the low 3's but a 2.56? Ive never seen specs for one that low. Anyone heard of a ratio this low before? Its an 81 12 bolt behind a Th350.
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Re: 2.56\'s gear ratio???

    Well I haven't heard of those gears. But the guy who did my lockright with me ( Marv thanks!!) put in a new pinion lock bolt (crossshaft, crosspin whatever) for me. It should be replaced anyway, even if it was not broken. It is part of what makes lockright work. The pin will wear out in 5 years with lockright and you replace it. /forums/images/graemlins/k5.gif

    BTW is the 16 really a 15 which makes it 2.73 and sounds right for a th350 truck in smog days /forums/images/graemlins/thinking.gif
     
  3. GMCLegacy

    GMCLegacy 1/2 ton status

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    Re: 2.56\'s gear ratio???

    i think 2.73 is as low as they went. and what the post above says about your 16 being a 15
     
  4. u2slow

    u2slow 1/2 ton status

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    Re: 2.56\'s gear ratio???

    They did make a 2.56 in the truck 12-bolt. A very 80's ratio. I guess they wanted the economy but hadn't invented the TH700 quite yet /forums/images/graemlins/thinking.gif

    Just a warning now... you can only re-gear to a max of 2.73 before you have to change the differential case.
     
  5. az-k5

    az-k5 1/2 ton status

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    Re: 2.56\'s gear ratio???

    Wow... 2.56... ouch /forums/images/graemlins/doah.gif Are you sure about the case change? Wouldn't that make 3 different cases running around?
     
  6. u2slow

    u2slow 1/2 ton status

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    Re: 2.56\'s gear ratio???

    Yep, 3-cases for the truck 12-bolt /forums/images/graemlins/eek.gif
    1) 2.56 to 2.73
    2) 2.76 to 3.40
    3) 3.73 to 4.11
     
  7. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Re: 2.56\'s gear ratio???

    I see where there are 3 cases also. Dug through the magazines and such here and found the write up which shows 3 case breaks. I will run into that later on as I have 3.08's now. 1 ton future but not until I can kil my 12 bolt. /forums/images/graemlins/thumb.gif
     
  8. jwduke

    jwduke 1/2 ton status

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    Re: 2.56\'s gear ratio???

    And just think, there is probably some mall cruiser, running this ratio, with 44's! ouch!
     
  9. 4xcrazy

    4xcrazy 3/4 ton status

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    Re: 2.56\'s gear ratio???

    Had a car once that had 2.29's in the rear, i thought i miscounted, until i counted 3 more times.
     
  10. 84gmcjimmy

    84gmcjimmy 1 ton status

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    Re: 2.56\'s gear ratio???

    /forums/images/graemlins/yikes.gif /forums/images/graemlins/yikes.gifWoah thats really high geared. (numerically lower)
     
  11. tarussell

    tarussell 1/2 ton status

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    Re: 2.56\'s gear ratio???

    A good friend of mine's first truck was a 1981 K-10 with 2.56's in it . We knew it had some sorry gearing in it from the test drive but were just discusted when we pulled the covers and found out that he had the the most unfriendly off-road gears ever offered in a GM 4x4 .
    Not long after that we installed 4.11's and an Eaton Posi in the rear just to make it bareable off-road with 35's .
     
  12. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

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    Re: 2.56\'s gear ratio???

    my 81 k10 came with 2,56s too . i thought my 305 was a complete dog but it was mostly the gears . /forums/images/graemlins/hack.gif
     
  13. R72K5

    R72K5 Banned

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    Re: 2.56\'s gear ratio???

    yep gear ratio from 2.56 to 3.08 is the cause of bad performance/acceleration, alot of ppl dont understand this at all


    the last 2.56 truck i came across was a 77-80 big 10 2wd pickup, it had 2.56 listed on RPO label, i still have the label somewhere around here, have had it for years, i snagged it back when i first started hunting for and saving RPO stickers from trucks



    my stepdad he has 2.73 axles under his 82 k10

    i been trying to tell him for years that he needs to find 3.42 or 3.73 axles for it, weve got this 86 k5 out here with good 3.42 front axle and he could get it real cheap but no matter how much i try to explain it to him he doesnt understand it all how it will help the ttruck perform and pul things for him,

    if i were him id be snagging the axle and hunt up a good 8.5" 3.42 rear for the k10 but he doesnt get it,..


    so il just let him keep on hauling gravel and boats with the truck until he blows up something again, he already burnt up the tranny once so far and had to have it rebuilt, i cant wait til he busts and axle or the 208 case or a driveline, but i guess thats what he gets for not being able to read or write at age 43, however he is very mechanically inclined and has photographic memory,.

    tradeoffs..

    just ;ike the tradeoffs of losing gas mileage in favor of better performance with lower axle(lower numerically) ratios
     

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