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Transmission Discussion of preventative/corrective maintenance and other technical issues regarding your coach's transmission.

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  #1  
Old 03-30-2010
Benson Benson is offline
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Default MT-40 Questions...

What is the correct fluid to use in a 1960's vintage MT-40 six speed Allison automatic?

I have seen conflicting info of either Dextron, Type-A, and Type C-2?

Any side effects or concerns substituting Dextron III fluid in a MT-40 made in the mid 60's?

I was also looking for some MT-40 maintenance or service manual info somewhere online with not much luck, does anyone have a good source?
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  #2  
Old 03-30-2010
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MT's went out of production in the early 70's so books are where you find them. Dextron is all you need, anything else is a waste of money. It was common to disconnect the retarder/clutch pedal linkage as MT's have a reputation for breaking input shafts, but that was due to incorrect manual shifting rather than retarder usage. It's a good plan to have a functioning trans temp gage with probe @ the 'to cooler' line, gets warm when using retarder and if you don't have air brakes you will be advised to have it working well. Retarder valve is located @ front curb side of the case, trans lines screw into the retarder valve body. MTs take off in third when the first two shifter positions are selected. In town use 3/4, save the top position for highway as you don't want the trans to hunt for gears.
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  #3  
Old 03-30-2010
Benson Benson is offline
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Mike,

Thank you very much for the great info. It was in regards to a tranny that has been sitting a while and was a little low on fluid. We did not want to run the vehicle without topping the fluid off. The dip stick did not say what type of fluid it took.

What is you opinion on the durability of the MT-40? Anything I should look for in a road test other than transmission retarder/temp issues, a burnt smell to fluid, or erratic shifting or slipping? Are all the parts available to do a full rebuild still?

I have never driven a bus with this transmission, can I expect hard shifting as normal? I remember ridding in an automatic equiped school bus as a kid, and you sure did know when it decided to shift.
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Old 03-31-2010
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The shift schedule of a MT is pretty interesting, gear changes interspaced with converter clutch apply and release can be difficult for one to abide if not familiar with heavy duty automatics. Shift points can be adjusted somewhat by moving throttle cable around, but generally full throttle opening should be about equal to full cable travel from the trans. Gas engine full throttle upshift should be about 3800/4000, diesel NA 2750/2900.
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  #5  
Old 08-31-2010
playswfire playswfire is offline
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I looked for a temp sending unit on my (MT-40) transmission, and found none.
I was thinking about addingone and can't tell which line is the "to radiator" line - how to tell? (I don't want to disconnect a line and fire her up and see what happens...)

Thanks
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Old 08-31-2010
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Quote:
Originally Posted by playswfire View Post
I looked for a temp sending unit on my (MT-40) transmission, and found none.
I was thinking about addingone and can't tell which line is the "to radiator" line - how to tell? (I don't want to disconnect a line and fire her up and see what happens...)

Thanks
John would temperature difference tell you? Flash up the cold engine and determine which line gets warm first. I would think that would be the line in. Just thinking here but I could be out 180 degrees. Has happened before.
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Old 09-01-2010
playswfire playswfire is offline
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Does the transmission get hot when idling in neutral?
I was thinking that the radiator might be heating the transmission in this scenario - but I could be overthinking this, maybe I just need to put a thermocouple on the pan and call it done.
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Old 09-01-2010
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John

Yes transmissons generate heat when idling,fluid still flows generating heat.
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Old 09-01-2010
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Some trannys do not pump fluid through the cooler in neutral,only in one of the gears.
Mike will know if thats true on the 6 speed allison.
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