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Old 05-08-2015, 12:57 AM   #21
Bus Nut
 
Join Date: Oct 2011
Location: Snowflake, Arizona
Posts: 323
Year: 1996
Coachwork: Blue Bird
Chassis: All American Rear Engine
Engine: C-8.3-300 Cummins MD3060
Rated Cap: 40 Prisoners
What you need to do is go to some of the RPM vs Speed calculators and determine
what Engine speed you want to have at a given highway speed. Cummins suggests
200 to 300 RPM over max torque rpm for best miles per gallon. They also say don't
run a diesel at max torque as it may shorten life of engine. Don't know if this is
applicable to the Detroit but I would think so. So determine your max torque RPM
add the 2-300 rpm then add the transmission ratio in high gear less the % of
slippage for the torque converter and divide by the differential gear ratio and
multiply by the tire revolutions per mile or something like that. then you can
change the differential ratio up or down in the equation to determine your best
ratio.
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Old 05-09-2015, 11:19 AM   #22
Bus Nut
 
Join Date: May 2014
Location: West Ohio
Posts: 626
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
Those figures sound about right, and I do believe it applies to all engine makes/models, with the exception of 2 cycle detroits. They seemed to run the best/most efficient when tached out.
When I was doing my rear gear vs trans swap I made and excel spread sheet where I could input the numerous variables(trans gear, axle ratio, tire diameter, engine speed) and it would spit out an rpm. I then correlated all that data into a graph so I could see my gear splits and top speeds and everything. I then made 3 or 4 different graphs to compare one trans and or axle combination to the other.
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Old 05-09-2015, 10:10 PM   #23
Bus Nut
 
Join Date: Dec 2014
Location: Florida
Posts: 584
Year: 1988
Coachwork: Blue Bird
Chassis: I.H.
Engine: DT360
Quote:
Originally Posted by Booyah45828 View Post
Those figures sound about right, and I do believe it applies to all engine makes/models, with the exception of 2 cycle detroits. They seemed to run the best/most efficient when tached out.
When I was doing my rear gear vs trans swap I made and excel spread sheet where I could input the numerous variables(trans gear, axle ratio, tire diameter, engine speed) and it would spit out an rpm. I then correlated all that data into a graph so I could see my gear splits and top speeds and everything. I then made 3 or 4 different graphs to compare one trans and or axle combination to the other.
Sounds great. Where is the link so we can all use it?
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Old 05-09-2015, 10:26 PM   #24
Bus Nut
 
Join Date: Aug 2010
Posts: 332
Year: 1995
Coachwork: Thomas
Chassis: International
Engine: 466DT
Rated Cap: 65
I usually use this one.

Gear Ratio Calculator

I like you can put in two different ratios. left side and right side then compare numbers.
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Old 05-30-2015, 05:38 PM   #25
Mini-Skoolie
 
Join Date: May 2015
Posts: 10
Find a TRUCK GEAR shop- give them the ratios and let them know what you are aiming for. These guys know their stuff and can order the ring and pinion sets- Do not go to a junk yard- There are so many risks in getting someone elses gear set- new bearings and ring and pinion to fit your unit. That is the way to do it right- a gear shop will set the lash and set the bearings to perfection. Its too big a issue to shade tree it.
Jack Google RIGHTGEAR.com
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Old 05-30-2015, 10:22 PM   #26
Bus Nut
 
Join Date: Dec 2014
Location: Florida
Posts: 584
Year: 1988
Coachwork: Blue Bird
Chassis: I.H.
Engine: DT360
Do you have an affiliate/associate in FL? California is too far to drive at 55mph and 2700 rpm. I tried Advanced Driveline in Orlando but they will only do the swap if I bring in the parts. They won't supply them, just install and then good luck.

Quote:
Originally Posted by Dirtdoctor View Post
That is the way to do it right- a gear shop will set the lash and set the bearings to perfection. Its too big a issue to shade tree it.
Jack Google RIGHTGEAR.com
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Old 05-30-2015, 10:50 PM   #27
Mini-Skoolie
 
Join Date: May 2015
Posts: 10
Go to a local truck repair (semi-Truck) shop and ask who they recommend for gear work.
The place that does transmissions will do the gear swap too. Even a dealer will do the work and guarantee it. I re geared a truck and it made all the difference in the world.
Jack
But do some homework- ask a local trucker where they would go. Most guys with dump trucks have a good shop they take their trucks too.
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Old 05-31-2015, 02:07 AM   #28
Bus Nut
 
Join Date: Feb 2015
Location: Cincinnati, Ohio
Posts: 539
Year: 2000
Coachwork: Blue Bird
Chassis: International
Engine: TE 444
Rated Cap: 12
I bought the whole differential assembly from the truck parts place, they have a guarantee on it, I could not buy a ring and pinion set for a spicer N190 (now N400) for $600, it would have been close to $1000 just for the gears then having to pay someone to assemble and set it up would have probably been several hundred more
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Old 06-01-2015, 12:19 PM   #29
Bus Nut
 
Join Date: May 2014
Location: West Ohio
Posts: 626
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
Quote:
Originally Posted by Kubla View Post
I bought the whole differential assembly from the truck parts place, they have a guarantee on it, I could not buy a ring and pinion set for a spicer N190 (now N400) for $600, it would have been close to $1000 just for the gears then having to pay someone to assemble and set it up would have probably been several hundred more
Exact same story here. I priced mine out through eaton and was looking at $1000+ in just parts. I would have done the work myself but 99% of people would have to add labor on top of that under the hope that the guy putting it together knows what he's doing. I'm not saying all used stuff is good, but most truck scrappers aren't out to con people into buying junk. Most of them will also include some sort of warranty with parts like that.
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Old 06-01-2015, 12:22 PM   #30
Bus Nut
 
Join Date: May 2014
Location: West Ohio
Posts: 626
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
Quote:
Originally Posted by HolyBus View Post
Sounds great. Where is the link so we can all use it?
I don't know how to link excel documents to a page. I don't think photobucket will do that either. I guess I could email it to you if you really want it. That link from hvbuzz looks pretty good.
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