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Old 06-23-2024, 06:49 AM   #1
Mini-Skoolie
 
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Engine: DT466e
Gear Ratio Advice Needed

I am considering changing my differential. I have a 2003 AmTran IC 40 foot RE with at DT466 and MD3060 transmission. My tires are 11R22.5 which I calculate to a 41.5 inch diameter. The current diff is a 6.50.

I have attached pictures of the tags from the diff and trans.

If the engine runs at 2300 RPM (I see this is a good cruising RPM, correct?)
https://www.strangeengineering.net/g...io-calculator/

Using the gear calculator this puts my 1:1 speed at 43.7mph. If 6th is unlocked (I think it is but I need to verify), that puts my cruising speed at 67mph (43.7/0.65).

First question. Are my assumptions and calculations above correct?
For best highway cruising, what diff gear ratio would be recommended? I'm headed from Florida to Wyoming and back in about a month.
Attached Thumbnails
Trans.jpg   Diff.jpg  

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Old 06-23-2024, 08:04 AM   #2
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Quote:
Originally Posted by melwade View Post
I am considering changing my differential. I have a 2003 AmTran IC 40 foot RE with at DT466 and MD3060 transmission. My tires are 11R22.5 which I calculate to a 41.5 inch diameter. The current diff is a 6.50.

I have attached pictures of the tags from the diff and trans.

If the engine runs at 2300 RPM (I see this is a good cruising RPM, correct?)
https://www.strangeengineering.net/g...io-calculator/

Using the gear calculator this puts my 1:1 speed at 43.7mph. If 6th is unlocked (I think it is but I need to verify), that puts my cruising speed at 67mph (43.7/0.65).

First question. Are my assumptions and calculations above correct?
For best highway cruising, what diff gear ratio would be recommended? I'm headed from Florida to Wyoming and back in about a month.
Your measuring shaft speed with that calculator or direct drive of the engine, you want to measure your overdrive in your figure.

Use this link for engine RPM\

https://purperformance.com/p-29669-rpm-calculator.html

Your transmission is very likely locked at 5th gear which is .75 overdrive. If you unlock 6th gear you would have a .65 overdrive.

Your current set up should have an engine RPM at 65mph of 2565rpm(assuming you only have 5 gears).

If you unlock 6th gear you would have a 2223rpm at 65mph

I currently have a gear ratio of 5.63 and I run at 2222RPM at 65 mph with a .75 overdrive.

Issue is, I hear it is very hard to unlock 6th gear. manufacturer a lot of times will decline the job
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Old 06-23-2024, 12:23 PM   #3
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There are people who have the Allison DOC software. You can send them your TCM (Trans Control Module) and they'll unlock 6th for $400. I also seen a guy that does them for $200 plus shipping. That's on the MD3060. I think the 2000 series is a bit more complicated, like a Valve Body Change or modification where they have to drill something out and install another valve or solenoid. I won't swear to that. You know the internet is NOT always 100% correct regardless of what the Facebook fact checkers say.

However, do the math and even with 6th unlocked, you're probably still not going to be happy. 6.50 is deep or low ratio for sure. Chances are if, you get the correct gear ratio, you'll be just fine with 5 speeds and sometimes you have to be careful with 6 speeds too. You'll get into a situation where it'll be "hunting" all the time. As in going back and forth often between 5th and 6th. All that gear changing tends to cause added wear, not to mention a PITA while driving it, so you either speed up or slow down to keep it happy.

Just don't go to high on the gear ratio or it'll fall on it's face climbing small hills or towing, and take 8 gallons of fuel to take off from a stop light to get all that weight moving. I see people switching to 4.10 and 4.33 and 4.48's That's pick up truck gear ratios, and then with those 41 in tall tires, now you're down to about a station wagon gear ratio and that's no good either. Having 5 speed OD with lock up converter transmissions in my 2 buses, I like the 5.29's I have. One of them has 11R tires, the ot her is a Handy Bus with flat floors so it has Toyota Prius tires on it as far as I'm concerned at 255/70R 22.5. I might be going to 11R on that one, but maybe not since if I do, I'd have to add wheel wells and do some metal cutting over the rear wheels.

But yeah, do your math calculators and take a look at 5.29's. I have no issues with setting the cruise at 70 and can easily get to 75 to pass a semi. The 11R tire bus will even touch 80 with the wind behind me if I'm not paying attention and why I normally just set the cruise at 70.
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Old 06-23-2024, 04:12 PM   #4
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I have a 7 window with a DT466 210 HP and MD3060--6th gear NOT unlocked-- and it came with 6.14 gears. I pulled my differential yesterday, and will be trading it in on a reman 5.38. With 11R22.5 tires-- that will translate to somewhere around 61MPH at 2000 RPM, which I think will be optimized. In my humble opinion. Now-- with a larger bus?

I have an older WTECII controller-- and getting 6th unlocked is sort of iffy/worrisome... I'm going to be happy with 5 gears. One overdrive.
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Old 06-24-2024, 08:24 PM   #5
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As stated many times here, I have DT466, 3060 unlocked, 42" tires 4.33 ratio equals 1600 RPM at 70 MPH. BUT my engine has timing advanced, pump turned up and larger turbo with highest boost of 23#. My donor engine/tranny is out of a dump truck and driving it home from Chicago area it would run 68 MPH with 6.5 rearend running max rpm of 2600 if I remember correctly. Hope this helps. If you don't get 6th unlocked I would look at mid to high 4's for gear, 6th unlocked low to mid 5's. I went to "Random acts of camping" last year in Nappanee Indiana and on those flats I got 16 mpg, usually is 10.
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Old 06-24-2024, 09:30 PM   #6
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Thank you for your responses. This is very helpful and the information I needed.
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Old 06-24-2024, 11:34 PM   #7
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There are people who have the Allison DOC software.
To clarify Allison DOC is not the only software needed to reprogram a tcm. That software is useful but not all powerful.
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Old 06-25-2024, 05:46 PM   #8
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If you have the touch pad for gear selection, when you put it in drive it will show the highest gear you have available. I found after unlocking 6th gear it did hunt between 5 and 6 a lot. Using the mode button cured that. My rear is 6.17, so I am at about 2200 rpm at 65, and max out at 75. I do not feel it has the power to gear any lower. Mine is set at 210hp.
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Old 06-27-2024, 02:24 AM   #9
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Originally Posted by PorchDog View Post
I have a 7 window with a DT466 210 HP and MD3060--6th gear NOT unlocked-- and it came with 6.14 gears. I pulled my differential yesterday, and will be trading it in on a reman 5.38. With 11R22.5 tires-- that will translate to somewhere around 61MPH at 2000 RPM, which I think will be optimized. In my humble opinion. Now-- with a larger bus?

I have an older WTECII controller-- and getting 6th unlocked is sort of iffy/worrisome... I'm going to be happy with 5 gears. One overdrive.
Great Gear Ratio Choice for either 10R or 11R size tires and OD transmission. So you'll be able to nicely cruise at 70mph. I know some like to cruise 65 too, either one 65-70 is a nice cruise speed. I think 70 is plenty fast enough and should be able to blend with traffic just fine in the slow or middle lane. I really like 2005 Blue Bird with ability to easily do 75 to get over and around the gorerned semi trucks and not have to take 2 miles holding up the fast lane to get around them long trucks. That 5.13, 5.29, 5.38 ratios, depending on which rear axle model you have, but those are all pretty close to equals. Blue Birds have a Meritor axle so they have a 5.29 ratio and the 5.38 is right there with is at only difference being .09 and not even noticable.

I've about decided to go ahead and keep my little tire bus with the 5.29's also. I wanted to go to 11R tires, but I think I'm going to keep my flat floors instead of adding wheel wells. Instead of going taller tires, I think I'm going to consider getting the 6th gear unlocked instead to compensate for the smaller tires and that oughta put my cruising rpms in the sweet spot.

I aslo agree with you, I would NOT open up 6th gear now that you have the better gear ratio. I think it would be hunting between 5th and 6th a lot and you'd end up just putting it in 5th. You'd have to drive 80 or so to keep it in 6th and every little tiny climb like going over a bridge, it would downshift back to 5th and back and forth.
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Old 07-05-2024, 09:36 PM   #10
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Thank you again for your responses. I have determined that my skoolie does have 6th unlocked. However, it appears to be governed at 60mph. It will top out at about 2100 rpm in 6th and 2500 rpm in 5th. Is this a TCM programming issue, or is it elsewhere?
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Old 07-05-2024, 10:54 PM   #11
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That setting for top speed is found in your ECM. Easy change with servicemax, Datalink connector and an old laptop

Or

Call and get a dealer to take it off.

Providing you are not password protected it's simple and you have the best scenario.

Mine is set higher than I ever want to drive. Believe speed is set to match engine govern speed on my rig. Don't think it has the power to do it unless downhill.

You have a good bus with that drivetrain setup overall. With a hp bump you could gear taller but that's another discussion.
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Old 07-06-2024, 07:25 AM   #12
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Quote:
Originally Posted by Hooker View Post
Great Gear Ratio Choice for either 10R or 11R size tires and OD transmission. So you'll be able to nicely cruise at 70mph. I know some like to cruise 65 too, either one 65-70 is a nice cruise speed. I think 70 is plenty fast enough and should be able to blend with traffic just fine in the slow or middle lane. I really like 2005 Blue Bird with ability to easily do 75 to get over and around the gorerned semi trucks and not have to take 2 miles holding up the fast lane to get around them long trucks. That 5.13, 5.29, 5.38 ratios, depending on which rear axle model you have, but those are all pretty close to equals. Blue Birds have a Meritor axle so they have a 5.29 ratio and the 5.38 is right there with is at only difference being .09 and not even noticable.

I've about decided to go ahead and keep my little tire bus with the 5.29's also. I wanted to go to 11R tires, but I think I'm going to keep my flat floors instead of adding wheel wells. Instead of going taller tires, I think I'm going to consider getting the 6th gear unlocked instead to compensate for the smaller tires and that oughta put my cruising rpms in the sweet spot.

I aslo agree with you, I would NOT open up 6th gear now that you have the better gear ratio. I think it would be hunting between 5th and 6th a lot and you'd end up just putting it in 5th. You'd have to drive 80 or so to keep it in 6th and every little tiny climb like going over a bridge, it would downshift back to 5th and back and forth.



thats what mine does.. hunts alot because im way over-geared in the rear.. im working on getting my gears swapped down so my 6th is actually useable.. I reprogrammed my TCM to turn 6th off unless im at really light throttle above 65 which i realy drive over that.. I want my 6th to be on when im running at 65 into moderate throttle going fro, 3.54 to 4.10 will net me that..
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Old 07-07-2024, 05:23 PM   #13
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Originally Posted by cadillackid View Post
thats what mine does.. hunts alot because im way over-geared in the rear.. im working on getting my gears swapped down so my 6th is actually useable.. I reprogrammed my TCM to turn 6th off unless im at really light throttle above 65 which i realy drive over that.. I want my 6th to be on when im running at 65 into moderate throttle going fro, 3.54 to 4.10 will net me that..
WOW, you've got to be kidding? So you've got a half ton pick up truck rear gear ratio. If you have 6th unlocked, I would sure be going lower than 4.10's. I'd be getting into the high 4's or low 5's. What size tire you running. That plays a part too. But yeah, if you're running a 10 or 11R tires, I'd get your money's worth. Keep in mind, low rpms is NOT always best as some think. Also think of strain on the engine. Your gear ratio is your torque multipler. The lower the gear, meaning higher numerically, is more torque multiplicaiton to the ground. So if your horsepower is XXX and you multiply that by 3.54 to the ground, or you multiply it by 5.29 to the ground... So you see how an engine can be struggling or strainging to climb a hill with 3.54's where as with 5.29's it'll climb a hill like monkey up a rope for a bannana. There's guys running 6.17 rear gears with 6 speeds and 11R tires and they're happy. That seems a bit to deep IMO, cuz I like to run 70mph and have the ability to do 75 to get around the goverend semi trucks without holding up the fast lane and taking 2 miles to creep around a 53 foot trailer plus tractor.

That's JMO, and if all I was going to change gear ratio for 1/2 of a turn on the driveshaft, I wouldn't even spend my money, that may not even be a noticiable gain and if it is, so minimal. Talk to others too and get their opinion, be sure you're getting money's worth. I don't know if you have a spicer or merritor axle so different ratios are available. Like Merritor runs a 5.29, Spicer runs a 5.38 so at a .09 difference, I'd consider those equal. But yeah, I'd for sure get down into the 4.88 or 5.13, 5,29 5.38 range and I think you'd be very happy with that and the .65 6th gear. I'm fine with my 5.29 and .75 5 speed, so I'd be tickled like a little girl if I had .65 opened up, and as said, I run 70 and still under the goverend engine RPM speed. Truth be told, I can even run 80 with the wind behind me on the 11R tires but I don't suggest that. No need to do it just cuz you can. Engine longevity, mpg and safety matter so I use 70 as my go to set Cruise Control speed. And NO, my 6.7ISB is geared the same, and it won't do no 80. It don't have the nuts to do it. That's my CAT C7 that'll run 80 if no head wind, otherwise it'll do 75 whenever I want it to.
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Old 07-07-2024, 06:10 PM   #14
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Originally Posted by melwade View Post
Thank you again for your responses. I have determined that my skoolie does have 6th unlocked. However, it appears to be governed at 60mph. It will top out at about 2100 rpm in 6th and 2500 rpm in 5th. Is this a TCM programming issue, or is it elsewhere?
Quote:
Originally Posted by Omnibot2000 View Post
That setting for top speed is found in your ECM. Easy change with servicemax, Datalink connector and an old laptop

Or

Call and get a dealer to take it off.

Providing you are not password protected it's simple and you have the best scenario.

Mine is set higher than I ever want to drive. Believe speed is set to match engine govern speed on my rig. Don't think it has the power to do it unless downhill.

You have a good bus with that drivetrain setup overall. With a hp bump you could gear taller but that's another discussion.
As said, it's in the ECM reading your VSS to limit the speed. I don't know what year or what powertrain you have, but most of these electonric tuned buses have different tune options from the factory. So it can be all the same engine as far as cams, injectors, pumps and all that and the tune it's given determines the hp/torque ratings. Buses tend to have the lowest possible tunes for the obvious. They don't need to go fast and lower tune usually means longevity and mpg. Just hypothetical, you could have a powerplant with 200, 240, 260 horsepower options. So a guess at 200hp tune. If you're going to get someone in there playing with the PROM (Program Read Only Memory)chip in the ECM, see if the have the tune to bump you up to the 240hp tune AND drop the max speed completely. Trust me, these engines are only going to go so fast and you'll still have the failsafe of the max RPM limiter and I'd keep that. Noone wants to hurt their engine so keep the RPM limited, tune in a few more ponies and you'll be able to benefit better from having 6th and bit more torquey can also stop the hunting between 5th and 6th and early downshifts.
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Old 07-07-2024, 06:29 PM   #15
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that bus has 19.5" tires.. (so yes near pickup truck size tires). (225/70R19.5) they are typically around 31.5" diameter tires.. so yes a 4.10 gear is what I plan to go to.. I dont want to be taching out at 2300 or 2400 RPM at 70 MPH.. thats why I swapped in an overdirve in the first place.. I was hammered at close to 2700 RPM at 70 MPH.. lots of noise lots of heat...



4.44 is a possibility (if i can find it), 4.10 is everywhere.. a 4.30 was offered but last I asked weller about it they said the gearset was near impossible to actually obtain for a 4.30.


I dont want to go too low and end up with a lot of noise and heat... while i dont drive that bus at anything over 70 (65 is my typical max speed).. i dont want the top speed to be so close to cruise that im against the limiter..



it has 8 lug wheels, I have zero intention of swapping its hubs to 10 bolt and spindles for bigger bralkes so I can install 22.5" wheels.. and i dont want the little brakes on big 22'5" wheels (i know 8 luggers exist).. besides 2 of my tires are brand new and 4 are only 5 years old...



so are you thinking I should look at a 4.44 instead of a 4.10? im sure it would bring my EGT's down further.. it looks like id be running about 2000 RPM or so at 70 MPH vs 1850 .. thats 6th gear.. the calculator seems a bit off.. either its off a bit on the math or my tires arent the diameter i think they are.. i need to roll off a full rotation of a tire and then calculate true rolling diameter..



the calculator im using seems to be lower than what the comouter reads for RPM.. if the engine RPM were truly off id have worse issues as its an electronic engine which requires the correct number of pulses per cam rev to fire the injectors.. so I tend to believe the computer on RPM..


good thoughts on this though.. I'll dive deeper into the idea of a 4.44 vs a 4.10. i think I need to make my real vehicle numbers match the calculator to be accurately estimatiming.. time to drive next to a tape measure..
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Old 07-08-2024, 01:04 AM   #16
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Cadillackid

I advocate rolling ten revolutions. Not just one. What kind of rear axle? Spline count? Abs ring needed?

William
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Old 07-08-2024, 06:36 AM   #17
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Originally Posted by magnakansas View Post
I advocate rolling ten revolutions. Not just one. What kind of rear axle? Spline count? Abs ring needed?

William

I responded to your PM.. it looks like its an S135 (360CA104-4X currently). which is 36 axle splines.. no ABS..



even though there is a label that says spicer 110 on it. it also has S135, and the build sheet for the bus has the carrier number I listed.



im not sure i have a tape measure long enough to do 10 revs but I could run a few back n forth and see where i end up..
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Old 07-09-2024, 01:29 AM   #18
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Quote:
Originally Posted by cadillackid View Post
that bus has 19.5" tires.. (so yes near pickup truck size tires). (225/70R19.5) they are typically around 31.5" diameter tires.. so yes a 4.10 gear is what I plan to go to.. I dont want to be taching out at 2300 or 2400 RPM at 70 MPH.. thats why I swapped in an overdirve in the first place.. I was hammered at close to 2700 RPM at 70 MPH.. lots of noise lots of heat...



4.44 is a possibility (if i can find it), 4.10 is everywhere.. a 4.30 was offered but last I asked weller about it they said the gearset was near impossible to actually obtain for a 4.30.


I dont want to go too low and end up with a lot of noise and heat... while i dont drive that bus at anything over 70 (65 is my typical max speed).. i dont want the top speed to be so close to cruise that im against the limiter..



it has 8 lug wheels, I have zero intention of swapping its hubs to 10 bolt and spindles for bigger bralkes so I can install 22.5" wheels.. and i dont want the little brakes on big 22'5" wheels (i know 8 luggers exist).. besides 2 of my tires are brand new and 4 are only 5 years old...



so are you thinking I should look at a 4.44 instead of a 4.10? im sure it would bring my EGT's down further.. it looks like id be running about 2000 RPM or so at 70 MPH vs 1850 .. thats 6th gear.. the calculator seems a bit off.. either its off a bit on the math or my tires arent the diameter i think they are.. i need to roll off a full rotation of a tire and then calculate true rolling diameter..



the calculator im using seems to be lower than what the comouter reads for RPM.. if the engine RPM were truly off id have worse issues as its an electronic engine which requires the correct number of pulses per cam rev to fire the injectors.. so I tend to believe the computer on RPM..


good thoughts on this though.. I'll dive deeper into the idea of a 4.44 vs a 4.10. i think I need to make my real vehicle numbers match the calculator to be accurately estimatiming.. time to drive next to a tape measure..
Wow, OK. Yeah You're probably in the right range then What kind of bus is this? Any pics? So if 4.10 is common then, is it possible you can scoop up a cheap used drop out 3rd member in 4.10 and install it yourself? If you can do that, then I'd say it's sure worth a try.
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Old 07-09-2024, 01:32 AM   #19
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Quote:
Originally Posted by magnakansas View Post
I advocate rolling ten revolutions. Not just one. What kind of rear axle? Spline count? Abs ring needed?

William
What is the purpose of 10 revolutions? Is this for calculation what the gear ratio is?
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Old 07-09-2024, 07:00 AM   #20
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Quote:
Originally Posted by Hooker View Post
What is the purpose of 10 revolutions? Is this for calculation what the gear ratio is?



get the true rolling circumference of a tire. you lay out a tape measure, chalk the tire, and drive next to it.. measuring the number of inches you go to make a complete revolution.



you of course use a rear tire and drive straight. Jacking up the vehicle and measuring the a tape is NOT accurate as the rubber does get a bit compressed from the weight so its best to actually drive off the distance.



william way is better as any error you make(ie is the mark exactly one revolution or are you back for forward a little) is divided by 10, ill get a 100 foot tape measure and do it this way..


ultimately it can also be used to program the speedometer in your dashboard as well, at least on International and freightliner (CAT based busses).



Allison transmissions output typically 16 or 40 pulses per driveshaft revolution.


so lets say for kicks that my tires are in fact 31.5" in diameter... to get the inches rolled by calculation.. I would do Pi (I use 3.14159) X D (diameter). (I know math purists say its 2 pi R).


so it comes to 98.960085 inches rolled per tire rev.


1 mile is 63,360 inches.


divide your tire inches rolled into your inches per mile. 63,360 / 98.960085
so that is 640.25814 tire revolutions per mile. an interesting tidbit is if you are driving 60 MPH, thats the RPM of your wheel


in the current setup my gear ratio is 3.54:1, meaning my driveshaft spins 3.54 times every time the wheel goes round once.



so multiply my tire revs per mile by 3.54 to get the driveshaft revs per mile. 640.25814 X 3.54 = 2266.51382



now in most factory Allison configurations you get 16 pulses per driveshaft rev. so multiply the driveshaft revs by 16 to get the number of sensor pulses per mile.


2266.51382 X 16 = 36264.2211



round up or down whichever you like and program your computer with the whole number in the "pulses per mile" parameter and thats how your speedometer is calibrated.. I tend to round up as over time the number of pulses per mile will increase as your tires wear down..



on the older internationals there are dip switches on the gauge cluster that can be set. ( i have the book with those.. i posted some it someplace here)..



these forumulas above can also be uses similarly to compute your speeds and engine RPMs as well as driveshaft RPMs..



this is the bus i am working with on the rear gear project.


its an 00 Bluebird CV with an IH 3800 chassis. was used as the "pregnant teenage mothers" bus at a district in Houston area.. it was built with a top speed of 70 on its original drivetrain. other than some interior paint and the digital dashboard, its all original fully seated. hydraulic ABS disc brakes but has factory air compressor for air ride rear and air seat. factory Air-Conditioning as well



it originally had an AT545 (1:1 top ratio) and i swapped in an allison 1000 (a performance built one by suncoast) 7 years ago.. it has a 0.71:1 5th gear and a 0.61:1 6th gear. it has its 6th gear open.



the engine is a T444E (think powerstroke 7.3), with stage 1 injectors, adrenaline HPOP, lines, and Orion tuner. I run my orion on stage 4 out of 7 and can still pass about anything I need to getting on freeway ramps.



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