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In search of opinions on gear change.

Discussion in 'Differential & Driveline' started by Vbb199, Sep 28, 2020.

  1. Grit dog

    Grit dog Full Access Member

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    I was editing as you posted...no worries, not pertinent info, just that IDGAF about mileage as long as it has some steel around it and doesn't drive like a turd-cicle.
    My dad had a 85? C10 back in the day. 305 turned 350 when we had to put a new (used) engine in it, very likely had 3.08s because it would just idle along at highway speeds.
    I recall it getting really decent mileage (carb engine), I was only 16, but compared to his old truck 74 Camper Special 454, my 455 76 Buick, moms 500 Caddy and my 400 70 Impala, it felt like 30 mpg. I could go all the way to northern WI on one tank of gas everything else took almost 2 tanks, except the 74 pickup. It would drain both saddle tanks and have to fill up before you got to the cabin!
     
  2. Vbb199

    Vbb199 B-rate Hillbilly Customs Supporting Member

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    I reckon gas was a bit cheaper then too!
     
  3. Camar068

    Camar068 Supporting Member Supporting Member

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    I had mine changed from 3.08 to 3.73. Even with the stock LS swap, it has it's lugging spot between 70-80 mph on the interstate w/hills. I wish I had taken @HotRodPC advice and done 4.10. It doesn't help that I went with 32" tires as well lol.

    I decided 3.73 thinking gas mileage, but it downshifts more on the hills in that range....which I think is decreasing my mpg for what I want it to do.

    I don't tow, so no help there.
     
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  4. Vbb199

    Vbb199 B-rate Hillbilly Customs Supporting Member

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    Much appreciated anyway. I think 4.10 for sure is where I'll go.
     
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  5. HotRodPC

    HotRodPC Administrator Staff Member

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    But you have to admit, you still had a significant gain going from Wee O Eight to 3.73's. Yeah, I think any of our trucks running an OD trans should go with 4.10s. But I also know you can always downshift to D with those 3.73's and get some pull power to climb a hill or a pass a semi and then go back to OD so you're still in good shape and probably getting a hair better mpg with the 3.73's since you should be right there around that sweet spot in OD locked up with 32's.
     
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  6. Grit dog

    Grit dog Full Access Member

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    I mean, yeah it was a buck a gallon back in the late 80s early 90s but Fortunately its about the same compared to inflation.
     
  7. Vbb199

    Vbb199 B-rate Hillbilly Customs Supporting Member

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    I remember gas being a little over 1$ a gallon when I was a little guy in the mid-late 90's
     
  8. Vbb199

    Vbb199 B-rate Hillbilly Customs Supporting Member

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    You mentioned that about pulling it down to D and got me to thinking, man, if I wanna pass someone now with a 3.42 rear and we're going 55-65 mph, With the power the engine makes, and that stout trans, I just slide down 1 gear, she slams into 3rd, and I take off and leave the mf's.

    I know with 4.10's it'll be even more impressive.
     
  9. Nonstop

    Nonstop Full Access Member

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    The nice thing about 4.10s is you will not need a carrier change. As you already know, those should be about perfect for you! Really wake up that engine.
     
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  10. dsteelejr

    dsteelejr Junior Member

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    Don't we all.

    My square.png
     
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  11. ballencd

    ballencd Full Access Member

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    First time I bought gas for a lawn mower it was $0.25 / gallon (1968). In 1972 with the oil embargo it went up to $1.50 and it freaked me out! : ) I was driving a $30 1965 VW bug getting 30 mpg at the time.
     
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  12. 75gmck25

    75gmck25 Full Access Member

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    I have 4.10 gears, 31" tires and a TH350, and it works really well for hauling. Having an overdrive to get RPM down on the highway would be icing on the cake.

    Bruce
     
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  13. Vbb199

    Vbb199 B-rate Hillbilly Customs Supporting Member

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    I'm pretty much dead set on 4.10's, gonna see if the wife will let me use some of our honeymoon gift money on a 4.10 gear set LOL
     
  14. MikeB

    MikeB Full Access Member

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    Actually, all of the ratios would affect comfort level (engine noise) and fuel mileage.

    That said, 3.73 has always been recognized as the ideal ratio for a 4 speed auto with .70 OD. Of course that's typically in a car or light truck with 27"-29" tires. If you absolutely must change, no way would I go past 4.10, even with 31" tires. The 4.10 gears would result in 19.9% more revs than 3.42 at any given speed. And 4.56 would be a whopping 33.3% more revs! Even if fuel mileage doesn't matter, that's a lot of noise under the hood at 85mph! You'd probably start driving closer to 70-75.
     
  15. dsteelejr

    dsteelejr Junior Member

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    If you're towing, at a minimum I would go with 3.73. At the most I'd go with 4.10s. IMO 4.10 gears are the lowest you'd want to go if you're still running those highway speeds. 4.56 and even 5.13 are just too low for highway speeds. You'd want those in something that is doing a lot of low speed grunt work, pulling heavy loads around town or extra torque for off road.

    I have two 3/4 tons (a 1973 C20 and a 1980 K25), both with 14 bolt 4.10 rears. My C20 has a 350 and has some good get-up-and-go for zipping around town with those 4.10s.

    Thats just my opinion, I could be wrong.
     

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