has anyone change axle gear ratio?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by VARITHMS, Oct 21, 2014.

  1. VARITHMS

    VARITHMS Medium Load Member

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    Nov 26, 2009
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    I'm looking for some input on changing ratio in a single axle truck. We are refurbishing a IH4600 with a dt466. Current drivetrain is eaton/full fs-1056n with a 1:0 sixth gear, 11r22.5 and a 4.33 drive axle for 2400rpm at 65mph on flat land with a dump flat bed gvw 32000 occasionally and very little wind drag. 1&2 are useless unloaded. While it is down we want to drop the 4.33 to a 3.73 or 3.91. Looking for a little mpg and 300 rpm less at 65&70.

    Any input from anyone who has actually done a ratio chage on any truck would be great. I did the search and found similar ideas but no final results.
     
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  3. 04 LowMax

    04 LowMax Medium Load Member

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    What about the possibility of a 2 speed rear axle? Very common in single-axle trucks. That would give you a good range, but, you'd have to select your ratios carefully so that the high is a faster ratio than what you have now.
     
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  4. VARITHMS

    VARITHMS Medium Load Member

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    Cost. A gear change in house is less than 1200.00
     
  5. Rocky64

    Rocky64 Medium Load Member

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    I recently swapped my 3.07 rears for 2.67.
    N-14, direct 10 speed, tall rubber 24.5.
    Its very permanent. I wish I would have only gone half as much, so I'll be swapping back to low pro 24.5 soon. Too big of rpm drop for my hot rod cummins.
     
  6. 04 LowMax

    04 LowMax Medium Load Member

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    Curious what that cost you if you don't mind? Did you just change ring and pinion or do the housing and all?
     
  7. Deezl Smoke

    Deezl Smoke Medium Load Member

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    Hillsboro Oregon
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    To go to 3.91 would be approx. a 250 rpm drop, and to 3.73 would be approx. a 450 rpm drop. The math is very simple to find the exact ratio you want, but the ratio availability may not be so simple.

    Find what axle and drop in you have, then find out whether you can run the ratio you wish wit the same carrier you have. Often a carrier change is needed when going from 4s to 3s, but not always. If a new carrier is needed, I'd bet it would be less expensive to trade your current drop in for a reman of the right ratio or a used one if it can be sourced locally.

    IMO.
     
  8. Cowpie1

    Cowpie1 Road Train Member

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    Kellogg, IA
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    OP, if you want to play with numbers and see how it all looks on a spreadsheet, I have a spreadsheet built that you plug in the tire rotation per mile (of the tire manufacturer website), the ratio of the gear in the trans, and the rear ratio. It shows the road speeds from 1200 - 1600 RPM, in 50 RPM increments. Simple to change the RPM's also. If you want, send me a PM with an email, and I will send it to you to use as you like. There are sites that have similar thing, but only one gear at a time. This sheet allows you to see how the relation is across the RPM band in up to 6 transmission gears side by side so that you can compare how a change would look across most of the gears in relation to one another.
     
  9. Pablo-UA

    Pablo-UA Road Train Member

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    I wanna change for "slower" axle on my Volvo, becouse roads are not good here and I have to drive at 50-55 mph. Will share results this winter, I belive
     
  10. uncleal13

    uncleal13 Road Train Member

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    I changed my 2006 Century from 3.58 to 4.11 as I was going to haul super-b's. I opted to change just the crown and pinions in both rears. Not much cost for parts but lots of labour. Total was $5,000 back in 2007. The front diff developed a bit of gear lash and eventually blew out the carrier bearings about two years later. I should have opted to just change out the whole carriers, more expensive option at the time, but less chance of someone goofing up the job.
     
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  11. Rocky64

    Rocky64 Medium Load Member

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    Vander Haag. $1200 for 2 assemblies that I installed in my housings. Any gear that starts with a 2.xx is going to be real cheap. High 3.xx and low 4.xx are most expensive.

    the actual repair I did was more due to my specific circumstances.
     
    04 LowMax Thanks this.
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