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Old 05-21-2020, 05:44 PM   #1
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Ford b700 trying to reach highway speed

Hello everybody I知 new to the group and have just purchased a 1991 blue bird school bus b700 with a ford 6.6 diesel.. I知 having troubles getting it to go over 45 I知 told to remove the governor any idea how I go about that?? Any help is much appreciated
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Old 05-21-2020, 05:56 PM   #2
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Hello everybody I知 new to the group and have just purchased a 1991 blue bird school bus b700 with a ford 6.6 diesel.. I知 having troubles getting it to go over 45 I知 told to remove the governor any idea how I go about that?? Any help is much appreciated
Is it a NC bus?

What rpm is the engine spinning at top speed?
YOu probably have really low gearing.
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Old 05-21-2020, 06:03 PM   #3
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I’m not sure I don’t beleive my bus has a rom gauge.. but at 45 it’s revved really high.. I’m not sure if my transmission just isn’t shifting into the next or what the problem is
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Old 05-21-2020, 06:11 PM   #4
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You'll probably find your rear end has some really low gearing.
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Old 05-21-2020, 06:13 PM   #5
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What rear end would I need? Or can I just change the gears is it? Would this be an expensive change?
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Old 05-21-2020, 08:13 PM   #6
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we need to know which transmission is in it first and the tire size
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Old 05-21-2020, 08:22 PM   #7
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we need to know which transmission is in it first and the tire size
trans code is cw diff is 54
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Old 05-21-2020, 08:33 PM   #8
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H-170 diff 6.83 ratio that’s what I’ve been told
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Old 05-21-2020, 08:33 PM   #9
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I beleive tire size is 9.00r20
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Old 05-21-2020, 10:41 PM   #10
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engine speed at 60mph

so, I figure about 517 tire revolutions per mile..... 6.83 rear end gear means at 60 mph IF you have one to one drive in high gear. then that means you spin the engine at 3,530 rpm......... or 58.85 revolutions per mile an hour.... that is a bunch for most diesel engines....... so lets see what a 5.38 rear gear will do....... at 60 mph with direct drive I have figured about 2,780rpm.... bout the upper limit and maybe even stretching it a little...

4.88 will put you at 2,500 rpm at 60 mph with a 9r20 assuming a 9r20 new is around 40" diameter and my math putting that tire at 517 revolutions per mile.

If my math is correct you are at around 2700 rpm at 45mph right now... so, if the motor can pull it on flat land with small head wind... then a 4.88 gear will give the about the same rpm at 60 mph

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Old 05-21-2020, 10:53 PM   #11
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found a 5.86

place in freehold new jersey........ that is the tallest ratio I have found so far.. Might have to buy entire axle.... might be cheaper to find scrap yard parting out busses and replace entire rear end..... I expect up to $1200 for entire rear end assembly..

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Old 05-21-2020, 11:07 PM   #12
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just starting

first look seems to indicate ratios 3.73 4.11 4.56 4.88 5.29 5.38 5.83 5.86

other gears shorter, but I dont think they are of interest to you

at least they made them... looks like three different gear carriers so you cant just buy ring and pinion.... have to stay within the range..

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Old 05-22-2020, 06:06 AM   #13
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I'd go 4.11 or 4.56.
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Old 05-22-2020, 06:45 AM   #14
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To find out what your trans is look on the side of the trans just above the oil pan on the passenger side and there is a data tag with the model no. on it
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