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gearing?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 78k5, Jun 18, 2000.

  1. 78k5

    78k5 1/2 ton status

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    What would be the best gear ratio for my 78, I have a moderately built 350, 350th running 35 inch tires. I have 308's now but have heard that 373's were what I needed. I just have no idea of what ratio to use.
     
  2. Blazer79

    Blazer79 1/2 ton status

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  3. chevy4x4

    chevy4x4 1/2 ton status

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  4. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color=blue>You're truck should have came with 3.73s if the auto was factory. Has the auto been swapped in? Could the axles be from a manual trans truck? The 3.73s are a little too numericly (sp?) low for 35s. You'd be better off with 4.10 gears. http://www.4lo.com has a gearing calculator that should help you a lot.

    http://www.chrisd71k5.coloradok5.com
     
  5. Jason73K5

    Jason73K5 1/2 ton status

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    I didn't have much of a problem with 35's and 3.08's with my 350/700R4 combo, but your 350 does make first gear a bit steeper. Right now I'm runing a 350/TH350 combo and 4.10's. On the highway the RPM's are a bit high for my liking but around town I think it's a great ratio. I have great acceleration(for a 4x4). The one thing that I don't do is rock crawling, so I can't tell you how it performs there, but I don't think it would be too bad.
     
  6. bablazer73

    bablazer73 1/2 ton status

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    hey chris, are your sure of your facts? my 76 and my 78, both auto's, 350/350 had 3.08 gears. bothbuilt that way from gm. had build sheets.

    your right. I don't understand the jeep thing!
     
  7. Black89k5

    Black89k5 Registered Member

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    If i u i'd go with 4.10's. But if it isnt going to be a daily driver go for 4.56's.
     
  8. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color=blue>I could be wrong, but that's mostly what i have seen. I've never seen a truck that came with an SM465 and 3.73s, but i've heard of them. </font color=blue>
     
  9. laketex

    laketex 3/4 ton status

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    I'd say 4.10s if you plan on driving on the street much. Your 35" tires, non-overdrive transmission, and 4.56 gears will be running over 3000 rpms at around 60. Especially cause your 35s prob aren't truely 35" tall. Now if you had a 700R4, go for the 4.56s.

    Bryan

    [​IMG][​IMG]
    Durant, Ok
    '79 Blazer in progress
     
  10. 89K5

    89K5 1/2 ton status

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    I need new gearing for my 35's too.

    30 miles on the highway to work every day. I have overdrive. IS 4.56 too much??
     
  11. ggallin13

    ggallin13 1/2 ton status

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    I have checked 4-lo.com, and from what I gathered there 4.10 gears are what you need with 35s. Maybe 4.56s are ok if you have overdrive (I do), but where I live there are lots of mountains and I'd be in third most of the time anyway, so 4.56s will be too hard on the motor, or so it seems. I am 85% sure that I will be going with 4.10 gears. That is, unless anyone has more info on the subject?
     
  12. bart

    bart Registered Member

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    I had the same situation...manual trans...36" tires...I bought 4.10's...looked at them for about 3 weeks...and thought about what I want to do with my blazer...and I promptly sent them back in exchange for 4.56's...
    I plan on doing some highway driving..but not a whole lot...or if I do it will be at reduced speed!
    I guess if you have a commute 30 minutes each day on the highway...go with 4.10's...if this is not the case...go lower...then you can always go with bigger tires later...or just launch real well off the line.
     
  13. Russell Keys

    Russell Keys 1/2 ton status

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    Does anyone run 5.13's with 35's? just curious.. I have 4.10 now and i'm not satisfied with the low end performance. I have a set of axles with 4.56 here in the shop but am not sure to go with them or buy brand new gears and possibly go with 5.13's, and like bart said it's a pretty good excuse to get bigger tires! This is mainly off road beater, maybe cruise town once a month. 350,th350,np203,35" boggers if anyone's reading-Russell
     
  14. 78k5

    78k5 1/2 ton status

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    Thanks for everyones help I was wondering what kind of rpm's I would be pushing with 4:56's at 60?
     

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