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Maxitorque Won't Downshift

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I have a 2004 Mack Granite I got recently with the 427 and Mack transmission. For the life of me, I cannot downshift it. It upshifts totally fine, but it will not downshift. Other people have tried and cannot get it to downshift. It only grinds. Sometime it can be forced to downshift, but will grind the whole time. 


Tried it all different ways, speeds, etc. It just will not downshift.


What could be wrong with the transmission m ? I think something is wrong with it. Considering swapping for an 8LL...

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Oops, yes, manual. Didn't know there were also autos. Should also say I am posting this for the owner who does not use online anything.


I will see if I can get the yoke checked.

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Trying to think of what could be wrong that would allow the sliding rings to engage on an upshift and not on a downshift.  I'm drawing a blank.  If a fork or rod was binding, it would not act like that.  Bad bearings?  Seems like it would do the same thing on an upshift.

I mean, if it will move to a place where it will grind, it should be as simple as matching the RPMs, and it should fall in.

Maybe The Brain Trust can come up with something.  Wish it was next-door so I could see it.

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"Eagles may soar, but weasels don't get sucked into jet engines."

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So let's try to get some more detail

When you say it wont down shift

Are we talking it wont split the gears, as in the air shift part of down shifting ?

Or it wont allow the gear stick to shift into lower gears, as in change down manually between by shifting the stick

Or is it both of these can not be performed 

Or maybe the range change is the issue 

I gather this is a 18 speed Mack ?

If so, from what I understand these are built along the same line as any other Mack transmission, just more refined 

A main transmission with the range change and split been seperate section bolted on, two seperate gear boxes close coupled 

It would be highly unlikely that all sections have failed at the same time

So if you  can establish which gears aren't down shifting it can help establish what part of the transmission has the issue or if it is the transmission at all

So is it the splitter on the side of the stick

The range change on the front

The stick it self

Or a combination of two or more of these




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5 hours ago, Joey Mack said:

Check the output yoke. See if it's loose..

Three things ! Loose yoke bolt, loose shift fork bolt! Now the hard one worn synchronizers !

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Sounds like a process of elimination

if you cruising along can u take the stik out of gear as in nuetral

let the engine go to idle revs

then rev upto the same revs as when U hit neutral

and the gear stik should slide back in to the same cog

no need for clutch on this proceedure


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