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Old 09-19-2015, 07:33 AM   #21
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Understanding Axle Ratios | Medium Duty Work Truck Info

for serious school bus-based towing...
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Old 09-19-2015, 08:51 AM   #22
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Thanks EastCoastCB, that was a very informative article. I can understand the ratio's better. The 4.10 would be very nice. How much does it cost to change ratio's on a used RE bus? What was your experience?
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Old 09-19-2015, 09:01 AM   #23
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I prefer FE buses and that's what I have. Ratios are the same regardless.
Price on swapping is in the 1000-1500 range, roughly.
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Old 09-19-2015, 09:40 AM   #24
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Below again is a tool that helps base gearing decisions on real data. You can play "what if" with virtually any combination before you spend any money.

Any change to the rear axle, tranny or tire size will alter the actual final drive ratio going to the ground. If you know a given engines power & torque curve you can gear to optimize it to your needs. But remember...what is perfect for a long haul highway cruiser is not what you need for something like a heavy load short run hauler. So, no matter what you wind up with, it will be a compromise. But if correctly balanced, one that will be appropriate to your usage.

Engine RPM Calculator
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Old 09-19-2015, 11:45 AM   #25
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Changing ratios in rear engine buses is more limited due to the reverse ring gear.

In a front engine bus, you can use a gear set from any medium duty truck with the same rear axle.

However, in a rear engine bus, it uses a special revers ring gear, and flipped rear axle housing not used on anything but rear engine buses.

So if there are 1000 gear sets available for the front engine bus, there will only be a few available for the rear engine bus, as the parts can only come from another rear engine bus.

I have never seen a rear engine bus around here with higher than 4.78. Most are 5.38.

This can change with geographic region due to the way the buses were ordered.

Also the Thomas rear engine buses are made superior in my opinion.
Much stronger rear frames, engine bay is laid out better, larger air cleaner, bigger retarder, and 6th gear unlocked on the ones with the MD3060.

Nat
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Old 09-19-2015, 01:30 PM   #26
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4.10 will get you 78 mph at 2700 rpm or about 65 at 2100 rpm if you have a mt643 or any other direct drive lock up tranny. With an at545 you are looking at about 67 at 2700 rpm due to slippage
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Old 09-19-2015, 03:57 PM   #27
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I do not expect to hit 78. I can live with 68, but don't want to expect too much. I assume that, the lower the rpm, the better. How low can one go with the proper configuration?

The Thomas RE models seem to have what I am looking for. Now it's time to find one in decent shape.
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Old 09-19-2015, 03:59 PM   #28
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How much weight you looking to pull?
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Old 09-19-2015, 05:23 PM   #29
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I am considering towing about 14,000 lbs. But that range should give me something to work with. I appreciate you interest and assistance.
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Old 09-19-2015, 08:33 PM   #30
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I don't think a RE bus is going to be the best choice for pulling that much.
It depends on how the rear frame is built. You'd almost certainly be exceeding the GVWR of most school buses though. My empty shell weighs nearly 18k on the scales and my Gross is 33k. With any kind of conversion and pulling 14k I'd be well beyond maxed out.
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