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Old 09-01-2018, 10:14 PM   #1
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Rear Diff ratio?

Im considering lowering the rear differential ratio on my Comfort bus.
I have a DTA360 attached to a ATA545 with 10r22.5 tires. Tire circumference is about 42 inches. Trans in 4th is a 1 to 1 ratio. Id like a rear diff ratio to allow 65MPH at about 2700-2800 rpm. Can somebody help figure a good ratio? Vander Haags has Spicer N175 diffs in a variety of ratios for $650 each. I figure this would be a better investment than a MT643 which has the same 4th gear ratio. Possibly get me better mileage since I dont haul anything and drive mostly 90% or better highway miles.

www.vanderhaags.com/detailview.php?part=24648952
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Old 09-01-2018, 11:16 PM   #2
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Plug your numbers into the bottom calculator...then you can play with any of them and see the difference.


Engine RPM Calculator
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Old 09-02-2018, 01:45 AM   #3
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super easy, thanks a bunch

That was super easy. Thank You for posting that link.
I'm going to try and get a 4.44 or 4.10 ratio. good options and keeps the engine in its power band. Id rather see 2100 RPM at 60MPH than 2900RPM
Now to make the purchase and swap em out.
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Old 09-02-2018, 09:59 AM   #4
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Roger that. Many benefits to be had by keeping a diesel in or near its' "sweet spot".


And most people are surprised by the differences even small adjustments can make. Sometimes you can achieve what you want with a minor change in tire size instead of a big $$$ re-gearing.


That calculator can be fun to play with. Glad to hear it helped.
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Old 09-16-2018, 12:41 PM   #5
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trans lockup?

Stop me if I'm wrong, but don't you have a transmission without lockup?

Wouldn't you benefit more from the transmission swap?

http://www.skoolie.net/forums/f33/mt...nay-24142.html

I just recently saw somewhere that someone had purchased Allison's back stock of older transmissions, including MT643s which they were selling for around $650.
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Old 09-16-2018, 03:11 PM   #6
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Yes, I have a AT545 in the bus. I have found a remanufactured MT643 to purchase. I have not found any of those surplus for $650. If anybody has a link to those, I'd gladly check em out.
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Old 09-16-2018, 04:44 PM   #7
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Quote:
Originally Posted by OrionsComfortBus View Post
Yes, I have a AT545 in the bus. I have found a remanufactured MT643 to purchase. I have not found any of those surplus for $650. If anybody has a link to those, I'd gladly check em out.

here is where I got mine.. im in the middle of the swap on a DTA-360 as we speak..


https://www.lkqheavytruck.com/part-d...ON&model=MT643


-Christopher
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Old 09-16-2018, 05:56 PM   #8
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Nice. It says it's been renewed/remanufactured by Allison. I'm going to call on Monday to find out. If it's accurate and shipping is acceptable. I may get that instead.
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Old 09-16-2018, 07:55 PM   #9
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Yep I just found that in my web history

cadillackid beat me to it

We've got a B300R so my big goal is to get sixth unlocked... rear axle ratio is 5.38. Sadly it's in a Blue Bird, so I would realistically need to get a TCM for that.
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Old 09-18-2018, 02:43 AM   #10
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I called and the price is good as well as the shipping. Sure beats $2,000 for the same thing. All that is left on my upgrade list is a DT466. Well that air disc brakes, insulation, new floor, better seats, ect.
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Old 09-18-2018, 10:51 AM   #11
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Yes, at that price, it seems too good to pass up.
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Old 09-18-2018, 02:10 PM   #12
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when I got mine i was told that these were ordered by Navistar to be remanufactured and they were stock for them in their warehouse.. used when a vehicle would come into the dealership needing a reman transmission... Navistar recently deleted them from their parts book and no longer wanted to stock them.. each one has a Navistar part number on it and was remanufactured by a navistar certified company..



LKQ bought up all the stock on them and has (had) a Bunch of them.. for those who have an AT545 and want an easy swap out if you thinkl your AT545 is dying.. they also had plenty of 545's for "$545"..



--Notes--

the included torque converter is designed for a DT466 engine. and the RPM shiftpoints are set at 2600 RPM.. you can use these really on any diesel engine with similar torque and RPM range as the DT466.. (DT-466E)..


these will NOT have the correct stall speed and RPM ranges for the high revving 9 Litre Diesel or any of the gasoline engines...



installing a 643 on a T-444E will require a Cross member.



the torque converter stall cannot be adjusted, however just like on a 545 there are in-pan hard stop shift adjustment wheels that can be tuned if you so choose.



on a mechanical DT360/466 you can fine tune your shift points by simply adjusting your modulator cable.. on a DT-466E you are stuck with an on/off electric modulator which is nothing more than a kickdown...



at WOT it should shift at 2600 or thereabouts regardless.. and even though a DTA360 can be run at 3000 RPM.. you dont want to shift it there.. its peak HP is at 2300. a DT466 also peaks at 2300 for HP.. so a buried in the floor shift of 2600. places you back into a solid portion of your powerband in the next gear...



-Christopher
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Old 10-06-2018, 06:32 PM   #13
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cadillackid Hows it going with the at545 to mt643 swap? I know the spacer has to come out and using shorter bolts for the flywheel/flexplate but is there enough room for the bolts/nuts to secure the flex plate to the torque converter? OR does it still need a spacer but much thinner?
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