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Old 02-23-2009, 04:13 PM   #1
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at545 to mt643 mounting questions

does anyone know if i can put an allison mt643 trans into my bus which already has an allison at545 without making new mounting brackets. id assume they have the same mounting locations.. im not worried about the driveshaft mounting, my question is just the actual engine and cross member mounting locations?
thanks
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Old 02-23-2009, 05:10 PM   #2
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Re: at545 to mt643 mounting questions

AT545 specs
http://www.industrialautomatic.com/html/at545.htm

MT643 specs
http://www.industrialautomatic.com/html/mt643.htm

According to this site, AT545 is SAE #3 bellhousing, and MT643 is SAE #2

This site shows SAE bellhousing specs; Unless your motor is drilled for both, it appears you'll need an adapter

http://www.foleyengines.com/FreeTechnic ... sings.aspx
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Old 02-23-2009, 08:30 PM   #3
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Re: at545 to mt643 mounting questions


Although I pride myself on being able to tell these two trannies apart, I'm still hoping to learn about the mounting flanges on engines. Are engine mounting flanges standardized also, or only the trannies?

What I do know, is that the bell housing IS the adapter between the engine and the tranny. To swap trannies, you need a bell housing that belongs with the tranny, as listed in the previous post.

What I don't know, is whether the other side of the bell housing also needs to match the specific engine model, or only a certain standard. Obviously, a little B series Cummins (5.9 liter) engine has a smaller mounting flange than a big 15 liter job in an 18-wheeler. But is each unique to the exact engine brand and model? If so, there would have to be a huge number of different bell housings out there. Anybody know?

Of course, if you buy a tranny with bell housing, from the same kind of engine as you have, you'd be all set.

Keep in mind, if you swap, you may need the correct flywheel / flex plate also -- I'd like to learn about this as well.

These two trannies are different in length, so you would need to shorten the drive shaft. Most larger cities have a commercial drive line shop that can handle that.
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Old 02-23-2009, 09:35 PM   #4
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Re: at545 to mt643 mounting questions

im elbow deep in driveshaft, lengths, angles yokes etc right now it is no fun. worth running away from
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Old 02-24-2009, 08:50 AM   #5
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Re: at545 to mt643 mounting questions

engine bellhousings are engine specific, some are just bolted to the back of the engine and some carry the rear main seal and also close up the back of the engine. IIRC the S.A.E. standard determines the diameter af the opening and attaching bolt pattern, also the distance fron the opening to the face of the flywheel is part of spec. this allows anyone to design a standard adapter to fit multiple makes of engines. this is useful for nonhighway applications such as power generation, hydraulic drives, marine drives etc.
typicaly engines in a given power range will have a standard bellhousing profile common to all driven components that require that amount of power to function properly, example at 545 is rated for less than 225 hp so it comes with sae 3 bell housing, at 643 is rated for up to 300 hp so it comes with a sae 2 bell housing. the examples are not actual specs, but for demonstration purposes only.
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Old 02-24-2009, 12:52 PM   #6
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Re: at545 to mt643 mounting questions


That's what I was afraid of -- engine side is engine specific. In other words, if Adamanderr buys a 643 with bellhousing on it, it still may not be the correct bell housing for his engine.

Good to be aware of.
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Old 02-24-2009, 01:36 PM   #7
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Re: at545 to mt643 mounting questions

oop's mis interpretation,
the engine side of the bell housing is engine specific, the trans side is standardized so that any SAE 3 bell housing "engine side" will mate up to any SAE 3 bellhousing "transmission flange"/converter, clutch housing.

a SAE 2 trans will not bolt up to a SAE 3 bell housing unless you change the SAE 2 flange to a SAE 3 flange.

hope this clarify's this some

SAE = society of automotive engineers,
the have a list of standardized definitions to help compare apples to apples and help minimize confusion.
bolt size, diameter thread count and hardness or grade
bellhousing size,#1, #2, #3, #4, #5, etc
definition of horse power, (torque X rpm) /5252 = hp with temps, barometric pressure, humidity and altitude corrected to a predetermined standard
etc
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Old 02-24-2009, 05:43 PM   #8
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Re: at545 to mt643 mounting questions

Quote:
Originally Posted by Elliot Naess
That's what I was afraid of -- engine side is engine specific. In other words, if Adamanderr buys a 643 with bellhousing on it, it still may not be the correct bell housing for his engine.
Ya know.... When I wrote that, I considered adding the words "of bell housing" to be sure there would not be any misunderstanding. But I decided it was not needed. I was wrong!

Let me try again:
That's what I was afraid of -- engine side OF BELL HOUSING is engine specific. In other words, if Adamanderr buys a 643 with bellhousing on it, it still may not be the correct bell housing for his engine.

Did I get it right now?

Picture of the two trannies, without bell housing, here:
http://www.skoolie.net/forum/viewtopic.php?f=6&t=1824
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Old 02-24-2009, 07:43 PM   #9
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Re: at545 to mt643 mounting questions

correct;

he needs to make sure that the trans bellhousing flange is the same as the engine bellhousing.

look at elkoskoolies post and the attachment about SAE bellhousing specs.
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