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Old 05-22-2023, 05:38 PM   #1
Join Date: Aug 2020
Location: Alabama
Posts: 193
Year: 1996
Coachwork: BlueBird
Chassis: International 3800
Engine: DT 466 Mech. Spicer 5 speed
Rated Cap: 34
Rear Axle Ratio thoughts---

Well, I have already been down this path, but watching Check Cassidy on YouTube swap his rear end has me scratching my head again.

My bus is short, 6 windows, and has a DT466 rated at 175 HP and 430 Ft Lbs of Torque. Lowest horsepower of all the DT 466 variants-- as far as I know.

It has a manual 5 speed transmission, which is direct in fifth, and a granny low gear. It came with a 4.78 axle from the factory. I have swapped in a 4.10 which puts me at 2150 RPM at 60 MPH.

Chuck has a midsize bus with a mechanical DT466-- I am sure it is higher horsepower than mine-- and an AT545. On his YouTube show he has swapped in a 3.73. So-- with direct drive (says he intends to install an MT643 in the future) that will put his 60 MPH RPM at 1960. (Assuming he has 265/75R22.5 tires like mine...)

So-- my swap from a 4.78 to a 4.10 is a 14% change.
Chuck's swap is from a 4.44 to 3.73 which is a 15% change.

Should I have gone lower-- maybe 3.91, or even 3.73 like Chuck?

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Old 05-26-2023, 02:49 PM   #2
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Location: Virginia
Posts: 2,227
Year: 1971
Coachwork: Wayne
Chassis: International Loadstar 1700
Engine: 345 international V-8
I guess what I have to ask is are you happy with what you have? As you get steeper in the gears the it will feel sluggish especailly on hills. If you up the horsepower then going lower would be nice. That engine should be happy around 2000.
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Old 05-26-2023, 03:43 PM   #3
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Join Date: May 2009
Location: Columbus Ohio
Posts: 17,843
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
so i have too steep of gear in my red bus.. even withy my engine cranked up to close to 350 HP (6 window short bus).. it hauls ass for sure but my EGTs go up real quick when I get on it and the RPMs are a bit low.. technically not lugging because it is gaining speed and RPM but I really need to gear down.. so there is definitely a sweet spot you want to stay.. for a low horsepower DT, 2200 RPM isnt bad for highway cruise.. you go taller and you will be shifting a lot.. now if you plan to Orion the engine or god-mode service maxx it up to a higher HP then a 3.90 would be a good choice for the rear end as the DT in higher HP forms will take quite a bit of fuel and not hate life. . (id still put a Pyro on it)...
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Old 05-26-2023, 04:09 PM   #4
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This is kind of an apples to oranges comparison. Chuck's automatic will mask any issues he might have with acceleration and grade climbing. You on the other hand having a 5 speed and granny low(really only 4 gears), will have a much harder time with it compared to him IMO. He will have to watch his 545, though, until he swaps to the 643.

On the other hand, you being lighter/shorter should make it easier for you grade climbing/accelerating, so it might all be a wash......

I think 2150 RPM at 60 MPH gives you a good all around gear. With the 4.10's, If you wanted to push 70mph/2600rpm, you can. But with a stick and city/highway driving I'd likely rather have 4.10's over 3.73's. Unless this will be solely an interstate cruiser, then the 3.73's would be preferable.

Truthfully, I'd keep what gears you have, and if you want to make a change, go with a different trans with more gears and an overdrive. Then you'd have the better rig all around. Maybe something like a super 10? It'd give you a lot of overlap being light as you are, but they're common to find and have some pretty good ratios.
My build: The Silver Bullet
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Old 05-26-2023, 05:10 PM   #5
Join Date: Aug 2020
Location: Alabama
Posts: 193
Year: 1996
Coachwork: BlueBird
Chassis: International 3800
Engine: DT 466 Mech. Spicer 5 speed
Rated Cap: 34
Thanks very much for this input.

I have spent the last year fixing minor issues and replacing 28 year old rubber hoses, and a whole lot of other parts in an effort to make the bus as reliable as possible. I do NOT want to have to be towed. My bus drove home to Alabama from Kentucky with no issues-- as people will often say. But the reality is there needed to be a lot of things done. All new brake calipers, brake pads, all new rubber brake hoses, three or four hoses around the fuel system that were darn expensive, a rebuilt brake booster that was leaking-- and a leak between the rear main seal carrier and the engine block-- bolts were loose. New clutch, pressure plate, throw out bearing, and flywheel(deep grooves). Driveshaft carrier bearing-- the rubber had deteriorated. Driver seat pedestal was broken, and the drivers seat needed reupholstered. My point is this has been a long fun process, and I have not even started the conversion. (well-- it's gutted, and the floor painted...)

The video by Chuck just made me question my previous choice of ratio. My calculation of the percentage change sort of answered my own question-- I was within 1% of the change that he made. Also-- it is sort of apples and oranges-- with the automatic versus a manual-- my goal is to be able to cruise at 60MPH on long stretches, and be able to climb minor grades without shifting-- so I will probably just stick with the 4.10.

One interesting thing I noticed was that the spacing of ratios-- 3.73, 3.91.and 4.10 each result in an approximately 100 engine RPM change at 60 MPH.

I love driving the thing. It's a hoot!
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Old 05-26-2023, 06:07 PM   #6
Join Date: May 2023
Location: Canada
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Year: 2001
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Chassis: International 3800
Engine: T444E, Allison 2000
Rated Cap: 72
Leave it. You made a call, it works, run it.

I've seen some of chucks videos, he has some good information but he contradicts himself to much for my liking.

You are talking about 2 different transmissions. An automatic converter makes torque at the expense of speed. Hence the name. You can go with taller gears and the engine will multiple torque through the converter to get a tall geared bus moving.

With yours being a standard with to tall of a final gear, while you can select the appropriate gear like an automatic, you loose that torque multiplication in turn causing acceleration issues.
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Old 05-26-2023, 08:14 PM   #7
Join Date: Aug 2020
Location: Alabama
Posts: 193
Year: 1996
Coachwork: BlueBird
Chassis: International 3800
Engine: DT 466 Mech. Spicer 5 speed
Rated Cap: 34
4.10 it is. Thanks guys for helping me think through this.
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Old 05-27-2023, 10:24 AM   #8
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Location: Eustis FLORIDA
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Chassis: Freighliner FS65
Engine: Cat 3126
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4.10 is good- no sense in changing it up.
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Old 05-29-2023, 01:57 AM   #9
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In your application I would stick with the 4.10 gears. Though I would be curious as to what ratios you have in the transmission. For allround use of your bus, 2150 at 60mph is a good speed setup with the manual. Continuous Interstate usage would deem a lower gearing but if it will be primarily a city/highway cruiser then the current 4.10 gearing is sufficient.

I myself was thinking about changing rear end gears on my CE200 from the 6.17 gears equipped to something lower like 5.57 or 4.88, given the VT365 in it. My reasoning was primarily to bring the RPMs on the engine down so the VT365 isn’t screaming along at 60mph. With the current 6.17 gears, 60mph puts me at 2200 RPM. Though I did see a few CE200s with the VT365 have different gearing to where the engine at 60mph was screaming along just about at redline.
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