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What gears for a 305 running 35s?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txbartman, Jul 10, 2001.

  1. txbartman

    txbartman 1/2 ton status

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    I am having my 35s put on today. I expect to see some low end torque problems since I only have a 305. I have 3.73s right now in my 10 bolts. They did okay with the 32s, but I think I need to upgrade. My truck is mostly a highway driver (daily) but also sees the off-pavement excursions. Was considering 4.56s. Figured this would improve my "power" (if you can say that for a 305) and not hurt my highway mileage too much. Hell, I only get 10-11 MPG now as is! What are y'all running?

    85 GMC Jimmy, 305 w/TH700-NP208, 4" lift, 35X12.5 BFG MTs, 15x10 Hellcats, Smittybuilt tube nerf bars and bumbers
     
  2. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    I am running 35s & 4.56s right now and still get a bout 10 MPG with no O/D. With that 700 I would say go with 4.56 or 4.88s. A friend of mine has 4.88s, 35s, & the 700 and loves it. He is up to about 15 MPG. The 4.56s will give you more options (the biggest plus is you retain the ability to crusie at hiway speeds in 3rd gear if you need to pull a heavy trailer.) You said you do a lot of hiway driving so 4.56s might be best for you, but I would at least consider the 4.88s.
    I don't know what your budget is but, after reading your other post (locker) you might want to skip upgrading that rear 10B. The one bennifet in keeping the 10B is you won't need a new carrier, it stays the same in the 10B. Other than that everything is a minus. With all the input you have given in your two threads I would be even more inclined to say go with the D60, OX Locker, and 4.56 gears.

    Jim '80 GMC & '73 Blazer
    Tread Lightly!
    <A target="_blank" HREF=http://www.gmck5.rockcrawler.com>http://www.gmck5.rockcrawler.com</A>
     
  3. rocko

    rocko 1/2 ton status

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    My 3.73's with my tired old 305 do just fine moving my truck down the road.. You shouldn't experience any problems..
    The only mod I did to my engine came in the form of header's to give it just a tad more power..


    A well armed society is a polite society.UPDATED <A target="_blank" HREF=http://www.rocko.rockcrawler.com>http://www.rocko.rockcrawler.com</A>
     
  4. Emmettology 101

    Emmettology 101 3/4 ton status

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    I was running 4.10's with a tired old 305 with my 35's without problems. It woudl get going just fine with my th350 and np208.... But if I had a choice, I would go with 4.56's....

    <font color=green>MIKE</font color=green> - "Hukd on fawnics,werkd fer me!"
    <A target="_blank" HREF=http://www.geocities.com/emmettology101>http://www.geocities.com/emmettology101</A>
     
  5. morphed86k10

    morphed86k10 1/2 ton status

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    I'd go with the 4.56's. They'll be a big jump from what you have already. In fact, you'll have more RPM with 4.56's and 35's than you did when you had 3.73's and 32's. I'd shy away from the 4.88's in a ten bolt because the gear strength gets pretty poor with gears that low.
     

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