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Gear Ratio??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Heath-La. 89GMC, Aug 16, 2000.

  1. Heath-La. 89GMC

    Heath-La. 89GMC 1/2 ton status

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    Just wondering..... What was the usual stock gear ratio on an 89 Jimmy. 350, 700R4 tranny. My truck has a strong engine, but couldnt pull my hat off my head. I was just curious to what it was from the factory.
     
  2. titanic

    titanic 1/2 ton status

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    I'm guessing... 3.08's -others will correct if wrong!
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I'd say its either 3.08's or 3.42's, but if it won't get out of its own way their probably 3.08's [​IMG]
    There was a thread not that long ago about this subject and I seem to recall someone had the codes for the different ratios. Apparently the code for the ratios is on the door, along with the other option codes.

    Rene <font color=red> 81 K-20 Jimmy </font color=red>
    <font color=green>[​IMG]"God hates a coward"</font color=green>[​IMG]
     
  4. tom

    tom 1/2 ton status

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    It's likely a 3.08 which I believe was the standard on that model. The code for a 3.08 is "GU4". Also I think it could be coded "GQ1" which means std ratio. My '91 came out of the facotry with both of those codes, and had 3.08's at the time.
     
  5. Derf00

    Derf00 1/2 ton status

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    Here's the codes:
    GU2 = 2.73
    GU4 = 3.08
    GU6 = 3.42
    GT4 = 3.73
    GT5 or GT8 = 4.10
    G80 = Gov-lock
    It could be the 2.73 they ran those to up the mpg on alot of Blazers and Jimmys.
     
  6. fr8train

    fr8train 1/2 ton status

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    Anyone know if those codes are the same for the '88 GMC Jimmys too?
     
  7. 90K5

    90K5 1/2 ton status

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    The codes are in my glovebox not the door but it is different for different years adn yes they are the same for Blazers and Jimmys.

    90K5
     
  8. Heath-La. 89GMC

    Heath-La. 89GMC 1/2 ton status

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    I just looked in my glove box.... It has 2.73. That sucks. I guess a good ratio to go to and still get livable gas mileage would be 3.42s. what do yall think. Im running 33s with an auto/overdrive trans. Id like to go to 35s one day in the near future. I think the 3.42s would be ok for that
     
  9. nyyef

    nyyef 1/2 ton status

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    this is how i classify raitos:
    for manual trannies:
    3.08s for 90/10, highway/offroad
    3.42s for 70/30, highway/offroad
    3.73s for 50/50
    4.11s for 30/70 and higher for off roading.

    for auto overdrive trannies:
    3.73s for 90/10
    4.11s for 70/30
    higher than 4.11s for more offroading.

    this is kind of my general guidelines.

    Knife.
    knife.coloradok5.com
     
  10. BigBurban

    BigBurban 1/2 ton status

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    I'd go <font color=red>AT LEAST</font color=red> 3.73s... <font color=red>ESPECIALLY</font color=red> if you're running 33s... If you're planning to throw some 35s on you really need the taller gear (start thinking 4.10s or 4.56s here). It's easier on your tranny to boot. Don't be fooled by low RPMs either. A truck that's geared correctly will get as good, if not better MPG than a motor turning low Rs, straining the motor, and jumping back & forth through gears, REGARDLESS of it spinning more RPMs... Been there and done that... Trust me, a taller gear is both you and your trucks friend when you step up in tire size. [​IMG]

    Here, this'll give you a pretty good idea of what you'll be dealing with... http://www.4lo.com/geartable.html

    [​IMG]
    http://www.geocities.com/crash607
     
  11. Blazer1970

    Blazer1970 1/2 ton status

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    Ditto BigBurb on this one. If you are going to run 33s, and you want to use OD on your 700R4, get 4.10s. This gear will still work OK with 35s, but 4.56s would be better. Lower RPMs do not always = better mileage. The 700R4 has a very steep OD at .7:1.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  12. lowlevell

    lowlevell 1/2 ton status

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    I had 3.42 in my 89 sub with 31's.I had no low end power.From 35mph + it was ok.Around 75mph+ it was damn fine=)I now have 4.10 with 31's.This knocked my rpms up about 300 or so,and knocked my speedo ahead 15-20 mph.Also going from 3.42 to 4.10 didnt give me as much low end power as i originally thought it would.Oh well time to cam it.Later...
     
  13. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Man, 2.73's and 33" tires with an O/D trans, do you run like 600 rpm at 55 mph....
    But seriously, if you are going to the trouble to change ratios I would suggest at least getting 4.10 gears.
     
  14. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    When I first bought my 81 Jimmy it had 2.76's with 33" tires and a 4 speed. I had to use first just to get it off the line. Of course on the freway it turned only 1700 RPM, so it had awesome passing power too (sarcasm intended). I have the 3.73's with 35's now, WAY better!

    [​IMG]
     
  15. Heath-La. 89GMC

    Heath-La. 89GMC 1/2 ton status

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    Thanks guys. Yall are right wbout the low RPMs in OD. When it stays in overdrive anyway. It kicks in and out of 3rd and OD all the time. Let me ask this.... Are the ring and pinion in the front and rear differential the same.... I mean, do they fit the same. If i find 2 rear ends that are the same as mine, but with, say 3.73s, will those gears fit in my front differential or will I have to buy gears specifically made for the front. Thanks
     
  16. Scoobydoo

    Scoobydoo 1/2 ton status

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    Forget 3.73's, and get 4.10's.
    3.73's would be OK if you already had them, since it really would not be worth the $$$ just to jump one gear ratio.
    but since you are buying them anyway, you should get the right one's, and the right ratio for 33" is 4.10! and they would be OK if you do ever step up to 35"s
    Also don't buy used gears! they will never seat correctly! best description I can give is it is kind of like putting new bearings in an old race, they didn't break-in together and will not get along w/ each other.
     
  17. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Sounds like good advice, I got the 3.73's because they were already in the 3/4 ton axles I bought. If I would have had to buy gears I definitely would have gone with 4.11's.


    [​IMG]
     
  18. WakeBoard&4X4er

    WakeBoard&4X4er 1/2 ton status

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    Re: Gear Ratio?? Same for ford

    I have a friend with a One Ton ford, is there a place to get the codes and # for a ford any where?
     
  19. WakeBoard&4X4er

    WakeBoard&4X4er 1/2 ton status

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    I have a friend with a One Ton ford, is there a place to get the codes and # for a ford any where?
     

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