# Allison Shifting problem



## rjb11632 (Dec 31, 2008)

I have an "89 Elite coach w/ a 3208 cat & an Allison mt643 trans the problem is when I try to toggle back to N from D the LCD goes blank for 2-3 seconds and then goes right back to D, this also happens if I go down to 3 or 2 etc. it goes down and doesnt want to come back up. I can get under the coach and shift it manually but it goes all the way past N to Reverse and then it will go to N from R. Does anyone have any suggestions?


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## dbarton291 (Jan 2, 2009)

RE: Allison Shifting problem

The MT643 was hydromechanically controlled and didn't come with any type of electronic display from Allison.  Does this vehicle have one of the Stone Bennett shifters in it?


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## rjb11632 (Jan 3, 2009)

Re: Allison Shifting problem

Yes sir, That is exactly what it has.


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## dbarton291 (Jan 3, 2009)

Re: Allison Shifting problem

Okay. The MT643 by itself does not move the selector on its own.  Any odd movement of the selector like you described, assuming I understand correctly, would have to be due to the shifter mechanism.

I recall in the 80s needing to send instructions for adjusting the Stone Bennett shifter to folks to relieve what they thought were transmission problems.  Many of these were air over hydraulic and could be a little finicky sometimes.

I have heard of a place called United Transmission Exchange utexchange.com that is a master distributor for Stone Bennett.  You might inquire of them.


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## rjb11632 (Jan 3, 2009)

Re: Allison Shifting problem

Im' not sure I explained that well enough, the selector does not move by itself, it is when I am trying to shift from D to N that I have a problem, and perhaps I should also have given a little background. This is our first coach.  We picked it up three or four weeks ago  just north of Miami, Fl and drove it home (very liesurely) back to  St. Louis, MO.  When we picked it up it shifted flawlessly, then the third or fourth day I had to try three times to get it to shift to neutral then it got steadily worse through the course of the next week as we made our way up the coast. By the time we got home, it would not shift in to neutral with the selector at all, when you tap the selector to go from Drive to Neutral it goes blank (as it always does for a split second before going in to N.) for a couple of seconds then just stays in D. It does shift in to R from N with no problems and from N to D and D to 3 and down to two and so on but will not come back up from forward gears toward N. I believe you may have answered my question already in your reference to the shifter mechanism. I can get under the coach and shift manually from D with my hand at the mechanism but it is a little stiff and goes all the way past N to R, then I get back in the coach and use the selector to get to N from R, but, the last time it took two attempts to get it to N from R just like the D to N scenario started. I guess my question now is, Is changing the shifter mechanisim a simple parts swap or is there something else I should know before attempting it? Also, where would I find one?  I'm sorry this is such a long post. I VERY MUCH APPRECIATE you taking the time to deal with my ignorance. THANK YOU, Richard


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## dbarton291 (Jan 3, 2009)

Re: Allison Shifting problem

I understand now.  You are able to move the selector manually.  I don't know at this point if the selector assembly is faulty, or simply needs adjustment or other maintenance.  My opinion would be to contact a Stone Bennett distributor and describe the symptoms.

If my memory serves me correctly, even if you change out the selector mechanism assembly, it will still need to be properly adjusted after installation.

United Transmission Exchange keeps coming up in my google searches on this subject.  I would start there and see if they can help with information on proper adjustment and maintenance on this shifter assembly and possibly prevent having to replace the assembly.  As a Stone Bennett distributor, I would think they would have parts also.


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## rjb11632 (Jan 3, 2009)

Re: Allison Shifting problem

Thank You, Again, I really appreciate your time and I will post what I find.


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## dbarton291 (Jan 4, 2009)

Re: Allison Shifting problem

Glad to help.  Let us know how it works out.

I forgot one thing.  Most Allison distributors have some experience with these shifters also.  To find authorized Allison service outlets, go to www.allisontransmission.com and click on the service locator.  I know there's an Allison distributor in St. Louis.  I think it's Western Engine company.

I would start with a Stone Bennett distributor though, because that's their business.  The Allison distributor is usually an Allison distributor, Detroit Diesel distributor, truck shop and other assorted businesses they get into.  Just my opinion.  Good luck and good travels.


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