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Old 08-27-2022, 01:10 PM   #1
Mini-Skoolie
 
Join Date: Aug 2022
Location: Virginia Beach
Posts: 37
Year: 1994
Chassis: 3600
Engine: dt408
Mountains in the at545

What revs should I keep my 1994 international Thomas vista fill size bud transmission at with the at545 when going through mountains?

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Old 08-27-2022, 09:07 PM   #2
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You should keep your transmission temp gauge under 210..


Need rpm for horsepower, but RPM generates heat on the at545..
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Old 08-28-2022, 09:28 AM   #3
Mini-Skoolie
 
Join Date: Aug 2022
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Year: 1994
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Engine: dt408
Just sucks cuz about 2600 rpm for me is like 53 mph smh and I know I shouldn’t take it that high of revs
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Old 08-28-2022, 11:20 AM   #4
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 17,159
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
Quote:
Originally Posted by BrandinoBeatz View Post
Just sucks cuz about 2600 rpm for me is like 53 mph smh and I know I shouldn’t take it that high of revs



you likely have a 6.50 or 7.17 rear end.. if your bus came from north carolina this was spec...


the extra low ratio means very low top speed and a lot of heat for your engine as navistar engines hate nbeing run at their RPM limiter.. they will do it all day long and you dont shorten their life doing so but they lose fuel economy doing it.



the low ratio is also EASIER on your transmission than a Taller (say 4.78 rear) gear... essentially its easier for the transmission to turn the wheels..


if you think about it like a 10 speed bicycle.. when you climb a hill you are in a low gear and the bike is easy to pedal but even pedaling as fast as you can , the bike doesnt go very fast,, shuft to a high gear and the bike will go fast (if you can pedal it.. because its hard to pedal)...


your bus is geared to go slow but standas a halfway decent chance at climbing hills.. while I dont drive fast in my busses.. 53 top speed would be unaceptable to me on freeways and barely acceptable on backroads..



if you re-gear the rear you could get higher top speed but just like a bike, the transmission would work harder.. not just from the ratio but from higher wind resistance created at higher speeds..



if you drive in 2nd gear at 15 MPH up the mountain grades you can probably keep the trans cool.. you'll have good engine braking downhill with the low ratio and again going very slow..



I darn near Burned up the AT540 in my Superior bus climbing mountains out west when I first got it.. that bus has a Gasoline engine with a carb so not near the torque of a diesel.. was empty except for seats(35 foot bus)


11R22.5 tires and a 6.50 gear ratio it had and I got the trans so hot I boiled the fluid out climbing a grade in wyoming..



it was about 65f outside.. that engine has a straight fan so the fan was roaring as i climbed the grade in 3rd gear.. engine temp was at 190 so my trans cooler in the radiator had a lot of room to work...



the rest of the trip i climbed the grades in 2nd gear at 15-20 MPH and I could keep the trans under 220 or right around...



ive regeared that bus to a 4.78 now, and on flat ground itll run 65 all day that 392 just purring away but climb a hill and the trans temp wants to climb right with me...


that Superior bus will never go in the mountains or if it does it will just be the low-grade east mountains.. ( like I-75 between ohio and florida.. nothing big).
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Old 08-28-2022, 01:19 PM   #5
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turn on the 4 way flashers.

downshift a gear and go half throttle.

3rd gear will put you around 40, 2nd gear will get in you in the 20s.

slow but steady wins the race.
they wont overheat if you don't lead foot it, they have the power to climb, just not as fast as a car.

if you try to keep up with traffic, you'll be sitting on the side of a long grade, overheated sooner than later.

good luck!
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Old 08-28-2022, 04:10 PM   #6
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Quote:
Originally Posted by turf View Post
turn on the 4 way flashers.

downshift a gear and go half throttle.

3rd gear will put you around 40, 2nd gear will get in you in the 20s.

slow but steady wins the race.
they wont overheat if you don't lead foot it, they have the power to climb, just not as fast as a car.

if you try to keep up with traffic, you'll be sitting on the side of a long grade, overheated sooner than later.

good luck!

with a top speed of 53 he isnt gonna make 40 in 3rd gear...
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Old 08-28-2022, 04:21 PM   #7
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sorry there, im no math wiz.

4 way flashers is the key, warn others you are slow.

don't look at the speedo,
downshift until you can go uphill without losing speed at half throttle. downshift 1,2 or3 gears, whatever it takes.
crawl up the hill at half throttle.

here in colorado, at half throttle, i'll start a climb at 45 and crest the continential divide at the same speed.

if i start out fast and overheat, i start the hill at 65, and crest the hill at 5 or 10 mph. the constant 45mph or what ever speed you hold is faster and doesnt overheat the engine/trans in the process.
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Old 08-28-2022, 05:10 PM   #8
Mini-Skoolie
 
Join Date: Aug 2022
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Year: 1994
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Engine: dt408
My rear end is 5.38
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Old 08-28-2022, 05:14 PM   #9
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OK unless you have really small wheels / tires then something is a amiss here.. with a 5.38 rear and regulat 10R or 11R tires you should be hitting 60....



are you running low profile tires?
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Old 08-28-2022, 05:18 PM   #10
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What kind of bus do you have?
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Old 08-28-2022, 05:31 PM   #11
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I think there Dayton tires not exactly sure the size , I think there like regular size, I don’t think it can get
get over 58 and that’s at 2700 - 2800 revs and I hear running that along time isn’t good
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Old 08-28-2022, 05:34 PM   #12
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Year: 1994
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I hear if I put like 4.1rear on it I could cruise 65-70mph at like 2200 - 2300 revs !!
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Old 08-28-2022, 05:35 PM   #13
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Hi

you have a few options if you want to keep the Vista

1. Regear the rear end, keep the AT545 as they are cheap and if you control heat they will pull and run all day
2. Re-gear and also swap to an MT643
3. look into options of swapping up to an Allison 2000. But with your 94 wire harness will need to figure out a stand alone solution to the TCM inputs as far as your throttle position

with your motor I would be looking at re-gearing the rear end (using a complete used rear) and trying to look for one from an activity bus.. maybe 4.44 rear end would be good

your goal would be a comfortable flat ground speed of around 62-64 at a comfy rev

yes you would work harder up hills, but you would slow down, downshift, and watch temps.. and add a cooler

most schoolies are after flat ground cruising speeds it seems

My Vista is a 1999 and has the T444E
I swapped out the AT545 that gave me a top speed of 57mph at 2600 revs for the Allison 2000 and now I cruise at 64mph at about 2000 revs.

I can climb a significant grade at about 55 mph (fancy gap)

I have a 4.73 rear end, and I have lower profile tires on our shorty than your longer vista


IF you can do a workaround for the TCM signals and are good with computers an Allsion 2000 swap would be the way to go

If I was in your shoes 3 years ago and I had the motor you have I would today have a an MT643 and a different rear end

Here's another thread giving some comparative numbers

https://www.skoolie.net/forums/f13/w...tio-19985.html

dave
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Old 08-28-2022, 05:48 PM   #14
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Quote:
Originally Posted by BrandinoBeatz View Post
What kind of bus do you have?

I have 3 different busses..


all 3 had AT545's at one time..


and then there was one - only one now has an AT545..(actually an original AT540)



one bus got a custom allison 1000 swap
the other got an MT643 swap.


likely you have 10R tires so a top speed at 2600 RPM of 55 or so sounds more like it vs 53 at 2600... Navistar dash panels are pretty inaccurate at best...


my bus that got an MT643 is a 7 window Carpenter IH 3800 with a DTA-360. it has 11R22.5 tires (dayton wheels) and a 4.78 rear.. that bus tops out at 2800 RPM (the DT360 spins comfortably a bit faster than the 466).. 68-69 MPH.. I usually drive it about 60 and its happy to do it all day.. climbing hills I drop to 3rd and hang out at 40-45.. closer to 40 if I have all 3 air-conditioners on.. (2 compressors)..


the red bus is a little 6 window IH 3800 Bluebird with a Tuned / injectored T-444E. it has 225/70R19.5" tires and a 3.54 rear end. it has a custom allison 1000 swap in it.. theres plenty of info on it here in the forum.. in 4th gear (which is 1:1 like an AT545 or MT643.. the bus top speed is about 70).. in 5th or 6th gear the top speed is way above any speed id ever consider driving a bus.. im waiting on parts to arrive so I can regear it from 3.54 to 4.10 and raise my RPMs a bit..



The superior is a 1978 IH Loadstar 11 window with a Gasoline 392 and an AT540 allison auto. it is running 11R22.5 tires.. it had a 6.50 rear end and topped out someplace around 55 with the engine screaming at 3000-3200 RPM (the max safe range for that gas engine).. I re-geared it to a 4.78 now it flat-land cruises at 65 around 2500-2700 and doesnt think twice about doing it.. it cant climb hills to save itself.. and I wont as kit to either.. its a classic that I cruise around in the general region..



none of the busses are converted to homes or campers.. the DEV bus is a mobile office / Dev lab but still has most of its original seats.. being it was a wheelchair bus it had lots of empty space already... I added a couple seats up front.
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Old 08-28-2022, 05:57 PM   #15
Mini-Skoolie
 
Join Date: Aug 2022
Location: Virginia Beach
Posts: 37
Year: 1994
Chassis: 3600
Engine: dt408
How do I know what rear end a bus has just looking at it? Is there a way to figure that out? Like let’s say I go to a junk yard or pick n pull or somthing
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Old 08-28-2022, 07:57 PM   #16
Mini-Skoolie
 
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Year: 1994
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besides counting the gears and pinion teeth? or is there?
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Old 08-29-2022, 06:27 AM   #17
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Engine: DTA360 / MT643
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there are a couple ways.. first off you need ot know what Axle is in yours.. ie S-150, N-175, RA-39 etc.. there were a lot of different ones used in school busses and rule of thumb is find a whole "chunk" (3rd member).. which is the center section of the differential from the same axle as yours.. it is possible to mix and match but then you get into needing to count splines and such as different axles often had different numbers of pinion splines as well as axle splines..



by far the easiest way at a junkyard is to find one that has a "chunk" already pulled out and inspected and for your axle.. on a full size bus they are a couple hundred pounds or more and a bit unruly.. taking one out in the dirt isnt going to be a fun task..



for instance here is an N175 with a 4.44, I just googled it up and it popped in.. not saying thats what you need or want but it shows the part ..


https://www.vanderhaags.com/detailvi...cf=parentmodel


if you really want to venture into a junkyard and pull one yourself (first off finding a yard that will let you pull underneath-parts is getting tricky these days.. ).


there are numbers stamped on the housings and you can look them up.. or if the bus is a navistar you can get the VIN from the bus and call a dealer and ask what the gear ratio was factory installed.. rarely do schools ever re-gear busses so chances of finding one that doesnt match the VIN is rare.. use that option sparingly unless you are going to use multiple dealers.. they are busy and more than one or 2 calls about whats my ratio and they will hate you..





if you are mechanically inclined you can put it on.. they are HEAVY and love to roll around... but you dont even have to take the wheels off to install one.. if your bus has air brakes then it will stay put with the parking brake applied on flat ground.. if you have a driveline brake you'll have to chock the wheels really good so the bus doesnt run over you..



I use ratchet straps with my tranny jack and its a pretty easy job.. clean the seal surfaces well and lots of gear-oil compatible RTV..


if you arent mechanically inclined then it will be a lot tougher just because of the heavy piece of metal and the learning curve
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Old 08-29-2022, 07:13 AM   #18
Mini-Skoolie
 
Join Date: Aug 2022
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Year: 1994
Chassis: 3600
Engine: dt408
Well I mean I’m no mechanic but I also am really willing to learn and put work into this bus and I’m no dumby lol but thankyou for sending that link! So that is what the part looks like im gonna need? Also I got a full build spread sheet on my bus from IH. It is a 5.38 ratio
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Old 08-29-2022, 07:16 AM   #19
Mini-Skoolie
 
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Engine: dt408
I think the axel says international N190
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Old 08-29-2022, 07:19 AM   #20
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Engine: dt408
I could be wrong tho
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