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Old 04-23-2024, 10:38 PM   #1
Mini-Skoolie
 
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Looking for opinions on axle or trans swap.

I have recently acquired a 1991 International bus with a DT360, At545 and a 5.38 axle ratio. I moved it to the home base. While in transit, I couldn't hear myself think because the bus was so loud. I was driving between 50 and 55mph. I think it was turning 2500 + rpms. That is insane. If I use the bus for a trip, it will be to the mental ward. Fuel consumption is probably much higher at those rpms.

So my question to all of you is, should I do an axle swap or transmission swap? I have an AT 1545 but that won't help lowering the rpms any because it's still 1:1 in 4th gear. I have seen rear diffs for sale for as little as $500 with 4.44 ratio. I do also own a Allison 2000 transmission but don't feel like going through the hassle of that swap.

What say you?

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Old 04-23-2024, 11:13 PM   #2
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I have a 5.29 rear and like it mated with a 5 speed. If I didn't unlock 6th, I may have wanted to drop to like 4.88 or something, but I have small tires. Transmission would better, but complicated and expensive. You might go for a 4.44 or 4.6 rear first and then do the tramny later if you need more.
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Old 04-23-2024, 11:26 PM   #3
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I'm not sure of the future of this bus so I don't want to sink more $$$ than necessary. Is changing the diff difficult? My tire size is 11R22.5. Not much I can do there.
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Old 04-24-2024, 07:21 AM   #4
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I have a DTA360 in my DEV bus. paired with an MT643 (now.. it was a 545 that grenaded).. and 4.78 gears with 11R22.5 tires..


at 60 im turning 2400 RPMs or so.. the 360 is not a powerful motor and even with those RPMs and the old 545 it would slow down on every bridge incline.. the 643 is much better but still slows down on hills.. I hushmatted the complete driver area when I rebuilt the not-so-wonderful quality of carpenter Body mated to IH chassis.. I also mnatted the doghouse and properly sealed it up..


this helped but its not quiet.. the 360 maxes out at 2800 RPM..



at 2000 RPM its gutless at 2600 RPM+ it just makes noise and heat..



the pump can be turned up in the 360 to generate more power.. but I couldnt see going to any taller than a 4.44 (and thats with turning it up a bit)...


when my 545 blew i chose for nostalgia sake to keep the bus fully mechanical and swapped in an MT643 which has made a huge difference in my fuel economy and overall driveability.. the bus never runs any hotter than 195 or 200 even in 100 degree texas heat and 2 A/C compressors going..


to me the ideal setup for driveability wouldve been to gear dfown to like a 5.39 and install an allison 1000/2000 set up for throttle-only operations.. this would allow for downshifting on inclines.. probably giving you a top speed of about 55 maximum and then upshifting to 5 (or 6) on flat ground for quiet cruising.. since I have another bus that literally hauls ass at whatever speed I choose to drive it easily, I kept this one all mechanical.. ive had the bus 8 years and the DT360 has given me zero trouble other than an exhaust manifold gasket and a couple small fuel / oil leaks here and there..
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Old 04-24-2024, 07:50 PM   #5
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You kinda answered your own question with already admitting to not wanting to do a 2000 series install so your left with gearing.

4.44 and no taller.

Keep in mind, taller you go, more power you squeeze out of that engine, the more slippage you will have in that convertor which can create more heat with that 545.

You will have a slow bus and if that's fine with you, gear down, lower your RPM's for the reduction in noise. You can lower it down further with a manual swap if your fine with it or a 643....mechanical convertor lock up to avoid the electronics and gearing.

If you do swap that diff, feel free to drive by my place and push your old diff out the door in front of my place. I was looking for a 5.38 this past fall.
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Old 04-24-2024, 08:43 PM   #6
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". I was looking for a 5.38 this past fall." Says the man with double overdrive. LOL.
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Old 04-24-2024, 11:04 PM   #7
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Thanks for the input. I'm working on insurance. Until that is figured out, I will just be cleaning out the bus.
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Old 04-25-2024, 04:44 AM   #8
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Quote:
Originally Posted by Iscalcrazy View Post
". I was looking for a 5.38 this past fall." Says the man with double overdrive. LOL.
I don't have a double overdrive. It's a 5 speed. Double OD came later on the 6 speed.

I currently have a 5.63 rear diff. Was looking for the 5.38 to run out 4th gear to governor if needed uphill at 55-60 mph. Just going to do it slower......
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Old 04-25-2024, 08:05 AM   #9
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Quote:
Originally Posted by Omnibot2000 View Post
I don't have a double overdrive. It's a 5 speed. Double OD came later on the 6 speed.

I currently have a 5.63 rear diff. Was looking for the 5.38 to run out 4th gear to governor if needed uphill at 55-60 mph. Just going to do it slower......

thats why I need to Gear down from 3.54 to 4.10, right now on my bus with a 444E, I run out 4th gear to 65-67 then shift to 5th... i'd like a little more torque and run out at 55-60 instead.. since i do have double OD
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Old 04-25-2024, 09:21 AM   #10
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Any of you that has an ra39 with a 4.xx series wanting a 5.57 look me up. I'll even do the swap work lol
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Old 04-25-2024, 09:23 AM   #11
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As far as what you should do cal, Start with the gear swap. Then move forward to the trans.

Turf learned the hard way that the 1545 isn't necessarily a nut/bolts swap. I'd say it's likely not going to be for you either. IDK if LKQ still has those reman'd mt643, but you might be able to offload your 1545 to a military guy that needs it and upgrade to an mt643 for the same price.
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Old 04-25-2024, 12:53 PM   #12
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I did the 545 to 643 Swap on my DT360 and it wasnt a bad job... the only parts i had to source was a new flexplate.. the 643 uses a flat flexplate where the 545 used a convex.. to get the right converter offset..

otherwise my shifter linkage i had to mod a little but not a lot.. speed sensor, reverse lights, neutral safety, modulator all swap over from the 545..

my bus is air brake so there's no drum park brake assembly.. if you have one, it can be a Pain to find and is pricey...



driveshaft had to be shortened.. i used the same yoke.

had to get shorter flywheel to crank bolts.. standard grade 8 are all that was on it and what i used.. with loctite..



cooler lines need to be adapted to I think its #12 ORB fittings.. I ran new cooler lines as one of the old ones wouldve been too short.



my 545 had a deep pan so the dipstick assembly moved right over too.



cant remember any other gotchas on that job. had to take some fuel lines loose to get to the cooler lines.. so re-priming the fuel system was a bit of a PITA.. the 643 weights like 700 lbs compared to 350 for the 545.. i used a mixture of transmission jacks and 10K ratchet straps to horse it up in there.


im a little 150 lb dude so even throwing my weight at that thing just made it rock on the floor and not slide! wheels were key to moving it around..


I do remember running my air suspension all the way up to get clearance for the transmission to go under the bus while on the jack.. then I dumped it for working underneath...
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Old 04-25-2024, 05:55 PM   #13
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As was suggested by the others here, start with the differential and then go on to the transmission if you so choose.

What I would suggest is going to an International dealer with the VIN of your bus, and see if they can pull up the line set ticket. It should give all the codes and options your bus was built with from the factory as ordered. Should also give you the option code and info for the rear axle. For example, my bus is a 2006 IC CE200, and the build sheet I had listed my rear axle as a Dana/Spicer 19060S and the line set sheet sheet showed it as a 19.8K 190 WE DANA 19060S.

If you can get the line set ticket, you should then have all the info on your bus that you'd need.
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Old 05-06-2024, 05:15 PM   #14
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I have the line set ticket that I call a build sheet. I'm in the middle of loading up a 26 ft Uhaul 4ight now. Maybe I'll post it next week.
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Old 05-12-2024, 03:23 AM   #15
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Take your time. No rush.

If the build sheet specifies the drive axle in the bus, you could then look up what other gear ratios were available for that axle and model year.

Some adjustment would need to be made to the speedometer, if the gear ratio was changed, for it to read correctly. Other research would need to be done as a precaution, in case the center section you plan to swap into the bus has different splines for the axles, or other issues that might hold you up in the swap.
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Old 05-12-2024, 04:23 PM   #16
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I have a 545 with t444e and 4.78 rear diff. I believe a rear diff change is not going to accomplish what you want alone. You'll need the diff and transmission change.

On mine at 65mph I'm pushing 2700 rpm. The diff change may give you -100 rpm

My 2 cents
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Old 05-13-2024, 07:38 AM   #17
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Originally Posted by nikitis View Post
I have a 545 with t444e and 4.78 rear diff. I believe a rear diff change is not going to accomplish what you want alone. You'll need the diff and transmission change.

On mine at 65mph I'm pushing 2700 rpm. The diff change may give you -100 rpm

My 2 cents
A diff change to a 4.44 with AT643 or direct drive manual would net 2350 RPM on 11R22.5 tires at 65mph.

If he stays with the 545. Add 150 RPM for slippage.

He has a DT360, assuming low HP engine. You wanna keep some revs in that engine. That's why I said no taller then 4.44. lugging an engine at low RPM has no benefit. You can make heat 2 ways. Lugging can drive up EGT's, over rev can exceed the cooling package.
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Old 05-13-2024, 09:32 AM   #18
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Quote:
Originally Posted by Omnibot2000 View Post
A diff change to a 4.44 with AT643 or direct drive manual would net 2350 RPM on 11R22.5 tires at 65mph.

If he stays with the 545. Add 150 RPM for slippage.

He has a DT360, assuming low HP engine. You wanna keep some revs in that engine. That's why I said no taller then 4.44. lugging an engine at low RPM has no benefit. You can make heat 2 ways. Lugging can drive up EGT's, over rev can exceed the cooling package.

my DT360 likes that 2300-2500 cruise range.. like i mentioned above the MT643 swap was a big difference in driveability.. a 4.44 might lug ut a bit trying to get up to speed.. the taller gears you put behind a 545 the more heat its going to make.. you will be foot to the floor more often running against that converter.. the 545 is Not a high speed heavy weight highway transmission, it was never designed for that..



somer of the clutch packs in an AT545 interchange with the GM TH-400, the torque converter can interchange with the GM TH-400.. the TH-400 was a CAR transmission.. the 545 is a great stop N go transmission..


the reason Many of these busses with 545's are geared so low with slow top speeds is that was a way the manufacturer alleviated stress on the transmission.. gearing it low meant the engine and driveline had to exert less torque to get the bus moving.. similar to like when you ride a bicycle.. you downshift (which is gearing down) so you can pedal easier..



the gears in a vehicle do the same.. transmissions do have low ratio first gears 9 thus why you shift).. howerver sometimes its necessary to run even lower gears so you use low ratio rear gears.. to help ease the stress on the transmission..


swapping out your rear gears to taller ones can increase your top speed but it requires more torque to get that top speed.. the engine must make it and the transmission must transmit it..



you wouldnt use a 1/4" socket set to take a lug nut off ... you'd use a 3/4" socket set and an impact...



so why do people keep using a 545 to travel all the way across the country and expect it to last and work as good as something else.. ??
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Old 05-13-2024, 09:50 AM   #19
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so why do people keep using a 545 to travel all the way across the country and expect it to last and work as good as something else.. ??
Because it's what they have. It's what a large number of buses had installed. And most don't know the flaws of one like you, I, and a number of others here do. It's honestly one of the few things that irks me when a seller asks 100k for a conversion that has an at545, as I'd bet big money a trans failure is in the buyer's future.

If the 545 had used value, I'd say pull it while it's good and sell it. But they don't, so grenade the f'er and then swap it to a better transmission. Heck, I can't even sell a used mt643 for 500 bucks, what's that make an at545 worth?
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Old 05-13-2024, 06:21 PM   #20
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Because it's what they have. It's what a large number of buses had installed. And most don't know the flaws of one like you, I, and a number of others here do. It's honestly one of the few things that irks me when a seller asks 100k for a conversion that has an at545, as I'd bet big money a trans failure is in the buyer's future.

If the 545 had used value, I'd say pull it while it's good and sell it. But they don't, so grenade the f'er and then swap it to a better transmission. Heck, I can't even sell a used mt643 for 500 bucks, what's that make an at545 worth?
Exactly.

Just the OP has a 2000 series but does not wanna swap it and has a good gear ratio for it if it's a 5 speed already in the bus.

However he is willing to purchase a rear diff to install. Likely will blow the at545. Then will be staring at a 2000 series and his old 5.38 ratio laying on the floor. Regardless. Not my time and money.
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