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Old 06-21-2018, 11:11 AM   #1
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Help with Gear Ratios

I am looking at a few buses at auction that have DT466 engines, AT545 transmissions, and a gear ratio of either 4.44 or 5.62. I hope to take these cross country, so lot's of highway driving. Are either of these suitable for that, and is one better than the other? Thanks for your help.
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Old 06-21-2018, 11:29 AM   #2
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AT545 is the least desirable transmission you can get, but it does work. I've driven mine around the country and back and while it could have been better I made it to the top of every hill eventually.

4th gear no the AT545 is 1.00. Don't confuse that with a lock-up gear, because it isn't. It's doing its best to spin the output shaft at the same speed as the input shaft, but in a very inefficient way.

My short bus has 19.5" tires and a 4.78 rear end, and MPG goes down really fast above 55mph. My big bus has 11r 22.5" tires and also 4.78 read end and seems good around 60 so far.

AT545 + 5.62 is crazy talk. You'll be redlining at 45mph.
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Old 06-21-2018, 12:47 PM   #3
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Originally Posted by tororider View Post
I am looking at a few buses at auction that have DT466 engines, AT545 transmissions, and a gear ratio of either 4.44 or 5.62. I hope to take these cross country, so lot's of highway driving. Are either of these suitable for that, and is one better than the other? Thanks for your help.
For cross country look for more than a 545.
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Old 06-21-2018, 03:36 PM   #4
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There is one bus that has an AT200o transmission, is that any better?

I guess I am wondering if I can get one of these buses for under $1000 if it is worth it?

How hard/expensive is it to change out a transmission later?

Thanks again.
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Old 06-21-2018, 03:44 PM   #5
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At2000 is a lot better for highway use. Changing transmissions is something you have to be nutty for, just ask Christopher!
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Old 06-21-2018, 04:06 PM   #6
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The bus with the AT2000 trans has a Cummins 5.9L engine.

So replacing a trans is a bad idea, how hard/expensive is changing your gear ratio?
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Old 06-21-2018, 04:49 PM   #7
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Quote:
Originally Posted by tororider View Post
The bus with the AT2000 trans has a Cummins 5.9L engine.

So replacing a trans is a bad idea, how hard/expensive is changing your gear ratio?
I would be leery of any bus where the asking price was only $1000.
The AT2000 is a much better trans than the 545. That combo of engine and trans is not bad, just not a stump puller. Replacing trans are not a bad idea, it's just going to cost a bit ($1300+ labor). I f I found the perfect bus and the only downside was the 545, I would not pass just because of the tranny if I had access to a 3060 or 643. Gear ratios can be changed by just replacing the center unit with a used one out of another bus, or rebuild with new gears.
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Old 06-21-2018, 05:15 PM   #8
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A school district as a bunch of buses at auction. Iím hoping to catch one under a thousand dollar, but they might all go to $3000. Just trying to do my research.
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Old 06-21-2018, 05:31 PM   #9
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Quote:
Originally Posted by tororider View Post
There is one bus that has an AT200o transmission, is that any better?

I guess I am wondering if I can get one of these buses for under $1000 if it is worth it?

How hard/expensive is it to change out a transmission later?

Thanks again.
2000 is MUCH better than a 545. Night and day difference.
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Old 06-21-2018, 05:33 PM   #10
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The bus with the AT2000 trans has a Cummins 5.9L engine.

So replacing a trans is a bad idea, how hard/expensive is changing your gear ratio?
2000 series with a 5.9 is a pretty nice combo. I've got a friend's bus rt now with that setup and its good.
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Old 06-21-2018, 05:47 PM   #11
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For cross country look for more than a 545.



I blew up my second AT545 this past weekend... the DEV bus transmission is History... I ramn that bus up and down the eastern-half of the USA's mountains quite a bit esp in summer.. so I figure I heated it up and destroyed it at some point...



I was a pretty big AT545 fan at one point.. mainly for reliability.. but having had 2 go bad (one in each bus) now im pretty much on the bandwagon of AT545 is great short trips and flat ground.. bit the 643,2000s, and 3000s(or a stickshift) are the way to go if you plan to road trip the country
-Christopher
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Old 06-21-2018, 06:06 PM   #12
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Quote:
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A school district as a bunch of buses at auction. Iím hoping to catch one under a thousand dollar, but they might all go to $3000. Just trying to do my research.
They usually start them around $1K with a $1500 reserve and the bids jump in the last 5 minutes, so don't expect them to stay at $1000 for long.

Go to your UserCP (upper left) and fill out your profile so we know where you are and a little about you.
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Old 06-21-2018, 10:12 PM   #13
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Ouch! Sorry to hear that Christopher. Must be time for an upgrade. No doubt you will fine tune whatever you throw in there.
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Old 06-21-2018, 10:23 PM   #14
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Christopher, you can have my AT545 when I get the 2000 installed, since I need your help with the programing part and wires
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Old 06-22-2018, 07:21 AM   #15
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They usually start them around $1K with a $1500 reserve and the bids jump in the last 5 minutes, so don't expect them to stay at $1000 for long.

Go to your UserCP (upper left) and fill out your profile so we know where you are and a little about you.
I'm not getting my hopes up, just trying to figure out if they are worth buying.

I will fill out my profile now, thanks.
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Old 06-30-2018, 05:01 PM   #16
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Gear Ratios

In our fleet (30), we have Chevys, Fords, Internationals and Freightliners. We have Detroits, Dt466E, T444E, Cummins 6.7, Cat 3126's, Mercedes MBE's. We have the 545 and the 2000 transmissions mated to all the above except the Detroits, they are all 545s. IMHO...the rear axle ratio is a lot more important than the transmission. Yes, the 545 is a 4 speed, but we have several with that transmission that are capable of cruising at 65mph fairly easily. We put a 3:93 (not positive about that. But it was for sure under 4:00:1) in a Freightliner with a Cat 3126 / 545 and that bus will go 75mph. However....we swung too far on that one. It's real slow coming off the line. We have decided that a 4:11 rear end with the 545 will easily give you 65-70mph. The 2000's yield higher mpg at lower rpm, but the buses we have those in are in the early 2000 model years and up. I have a 2007 Meecedes/2000 that will get over 10mpg if you keep it around 62mph. That bus is easily capable of 75mph+. Our speed limit is actually 55. We stretch it a little sometimes on the interstates. We seem to have more trouble out of the 2000 trannys. Not sure if its a problem, or just that we drive those more since they are in the newer buses. And they cost more to fix. Any yellow school bus you get from NC surplus will have the 545 transmission with that stump puller rear end. They are not eligible for sale to the public until they are at least 20 years old unless they have over 250000 miles.
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Old 06-30-2018, 05:42 PM   #17
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Christopher, you can have my AT545 when I get the 2000 installed, since I need your help with the programing part and wires

I tend to use busted stuff as an opportunity rather than a failure..
being an Old hot-rodder it was pretty normal to perform "highly Encouraged Upgrades.."



I went and got a Reman 643 and am going to put that in. I had thought about doing a used 2000 update.. esp seeing as how I have a couple TCM's laying around.. but that bus is borderline classic and I like the idea of keeping it all mechanical. with its 11R tires and 4.78 rear.. the 643 will let me cruise at its comfortable pace of 55-60 all over the place.. plus now i can "turn up the smoke" on the DTA-360 a little and not worry about wasting the transmission..



no worries I'll help you get your 2000 electronics up and running ..

-Christopher
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Old 07-03-2018, 03:01 AM   #18
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Quote:
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I am looking at a few buses at auction that have DT466 engines, AT545 transmissions, and a gear ratio of either 4.44 or 5.62. I hope to take these cross country, so lot's of highway driving. Are either of these suitable for that, and is one better than the other? Thanks for your help.
A bus with a DT466 is going to be a pretty good running bus. But some of them were mated to the AT540 transmission which usually meant the engine was a low HP version. I have seen DT466's with HP ratings as low as 160 HP. You won't find a DT466 mated to an AT540 with more than 190-210 HP. Any more HP required the MT643.

A 4.44 gear ratio is going to allow a top speed in the 60-65 MPH range but if it is less than 190 HP every hill will slow it down. Even a serious headwind will slow it down.

A 5.62 rear ratio is going to allow a top speed in the 45-50 MPH range. Even with 190 HP it won't slow down that much on big hills. But the ability to keep going on a hill is going to be overshadowed by the fact that out on the flat you won't be able to go the speed of traffic unless it is downtown Seattle doing drive time.

One of the things a lot of people forget is it not only takes proper gearing to go the speed of traffic but you have to have the HP to do it. Most school buses delivered with low HP rated engines and slow top speed rear end gear ratios will not be able to go much faster with faster gears simply because they won't have enough HP to do so.

The power requirements to go faster goes up exponentially the faster you want to go. Suffice it to say, if you need a bus to be able to travel long distances at highway speed you need to find a bus that can do that before you purchase. The cost to retrofit and upgrade is going to be quite a bit more spendy than purchasing a bus already set up to go highway speeds.

To increase HP it isn't just a matter of turning a screw, reprogramming a box, or installing larger injectors. In addition to the more HP you are also going to have to upgrade the cooling system. Most school buses have adequate cooling capacity. But if you raise the HP the cooling ability is not going to be enough to use the HP. So you will have the HP to go but the cooling system won't be enough and you will overheat.
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Old 07-03-2018, 10:47 PM   #19
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Quite interesting remarks regarding transmissions and gear ratios. I bought my bus a year ago with a two-year deadline (by wife) to convert. It has been sitting in my backyard unconverted but worked on for almost a year. Yesterday after reading the discussion in this thread I contacted the manufacturer (or assembler) Wolfington and got a response right away. I have a Wolfington Bus Company production with coachwork by ATC (American Transportation Company) and an International chassis, 11 windows, 54 passenger capacity. It was built 10/2001, titled as 2002. Miles: 114K. The engine is T444E and now I have learned the transmission is Allison 2400 and gear ratio 5.57. What can you say about this combination?
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Old 07-04-2018, 01:24 AM   #20
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I blew up my second AT545 this past weekend... the DEV bus transmission is History..

-Christopher
WHAT?!?!?!

say it aint so

i can't say i recall any rear end changes on the forum but im sure there have been some. the math makes sense to start at the pumpkin and work back to the trans and not the other way its done here. mines a 4.78 and i max out at 67. a 4.10 rear ought to get me up to 75.


really Chris? a 643?

j/k
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