Rear Axle Ratio thoughts---

[PorchDog]

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?

[Ronnie]

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.

[cadillackid]

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)...

[Booyah45828]

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.

[PorchDog]

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!

[Omnibot2000]

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.

[PorchDog]

4.10 it is. Thanks guys for helping me think through this.

[EastCoastCB]

4.10 is good- no sense in changing it up.