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Old 10-25-2016, 12:44 PM   #1
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Rear end ratio change.

I'm really wanting to change my ratio of my rear end from 4.78 to 3.73 if I keep my bus to make highway speeds more attainable. I found a remanufactured rear end for 1500 with core deposit. The local shop said it would only be about 3 hours of labor plus fluids. So out the door at 1900. Does this sound reasonable? It seems a little silly as I probably wouldn't see a return in the investment for years. But would make driving much more comfortable.

What does everyone else think?

Bus is 1993 Amtran Genesis DT466 MT643
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Old 10-25-2016, 01:21 PM   #2
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keep us posted on the swap.

i have the same 4.7 differential and spent plenty of time thinking about doing the same. your DT motor should make enough power to make use of the taller gear and get more speed, or cruise at the same speed your at now at a lower rpm.
if you're going to see a lot of interstate time, it'll be a nice upgrade.
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Old 10-25-2016, 01:30 PM   #3
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I've got the same bus, with 4.44.
Have you looked into running a bigger rear tire? I doubt it would be as dramatic a difference, but could be a better investment. Especially if your tires are worn.
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Old 10-25-2016, 01:44 PM   #4
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I actually may have 4.44 as well. I'm doing 60 mph at around 2250 RPM.

Wouldn't that only give about 3 mph difference? I do need two rear tires. But the other two are pretty good
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Old 10-25-2016, 02:36 PM   #5
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i may be wrong, but i believe the speedometers are run on their own gear off the transmission. either rear end or tire swap will get you faster but your speedo will still read the same based on rpms.
fwiw
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Old 10-25-2016, 03:41 PM   #6
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Quote:
Originally Posted by bread519 View Post
I'm really wanting to change my ratio of my rear end from 4.78 to 3.73 if I keep my bus to make highway speeds more attainable. I found a remanufactured rear end for 1500 with core deposit. The local shop said it would only be about 3 hours of labor plus fluids. So out the door at 1900. Does this sound reasonable? It seems a little silly as I probably wouldn't see a return in the investment for years. But would make driving much more comfortable.

What does everyone else think?

Bus is 1993 Amtran Genesis DT466 MT643
Cost seems reasonable. However, you probably don't need to replace the entire rear axle - assuming the desired gear set is available for your current one (and given you're finding a reman, I'm assuming there is). I located a shop that would redo my axle module with my desired gearing for ~$850 or so (exchange), and with a transmission jack, this can become a DIY job (the module is somewhere around 300-350 pounds).
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Old 10-25-2016, 03:42 PM   #7
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i may be wrong, but i believe the speedometers are run on their own gear off the transmission. either rear end or tire swap will get you faster but your speedo will still read the same based on rpms.
fwiw
CadillacKid can explain better than me, but the gauges are easy to recalibrate.
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Old 10-25-2016, 03:43 PM   #8
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I actually may have 4.44 as well. I'm doing 60 mph at around 2250 RPM.

Wouldn't that only give about 3 mph difference? I do need two rear tires. But the other two are pretty good
Check out some online gear ratio/speed calculators. You can plug in different tire sizes and stuff and see what you'd gain from what.
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Old 10-25-2016, 03:45 PM   #9
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I think you're right.... a rear end swap would require dropping a new speed gear or sensor in that's calibrated to the new gearing to keep the speedometer and odometer accurate.

YMMV, they may not all be the same way. Check it out to see what, if anything, needs to be done on that side of things.
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Old 10-25-2016, 03:46 PM   #10
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I think you're right.... a rear end swap would require dropping a new speed gear or sensor in that's calibrated to the new gearing to keep the speedometer and odometer accurate.

YMMV, they may not all be the same way. Check it out to see what, if anything, needs to be done on that side of things.
Internationals' are adjustable. no need for any new parts.
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