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It is my understanding, (correct me if I am wrong) that in normal mode, the torque converter stays unlocked until you reach a certain road speed/engine rpm in top gear. In the T/H mode the torque converter locks as soon as you shift out of first gear, regardless of engine speed/road speed.


It would seem that it might be an advantage to run in the T/H mode all the time, and gain some fuel economy, yes/no? I just took delivery on mine last night, so forgive me if this is a dumb question.
 

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Not a dumb question. In regular mode I believe the TC locks up in 4th and 5th (someone will have to correct me on that). In tow haul, the TC locks up in 2nd, 3rd, 4th and 5th. It is said that if you drive around in tow haul you could get worse mileage because it holds you in gears longer than normal mode due to the fact it changes the shift point. I have not tried it for a tank, so I can not say for sure whether you would get worse fuel mileage or not. But it does make sense..
 

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Only dumb questions are those that are not asked.


Don't know how long you've owned your truck but you'll learn the traits of tow/haul the more you use it.


Every morning I use it to help slow my empty truck going down the hill by my house.


When camper is on always in tow/haul.I'll take it out of t/h to force a 4th to 5th shift when running loaded as conditions allow and the push the t/h button again to get the grade braking back.


Its a really neat transmission and I'm surprised how much I use the t/h mode even when not towing/hauling.


I believe Mac runs around with his in t/h all the time.I seem to remember him saying that over on TDP.I might be mistaken though.
 

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The grade-braking algorithm's primary purpose is to utilize engine braking to slow a heavy vehicle on steep grades in order to reduce wear on the traditional braking system. The method used to slow the vehicle is by overriding the PRNDL position, effectively pre-selecting the next lower gear range automatically. Because the transmission is electronically controlled and there is no mechanical linkage that needs to be moved for a pre-select downshift, implementation of this algorithm can be done completely in software with no hardware modifications.


This algorithm takes into consideration several factors before commanding a pre-select downshift. These are the primary inputs:
<UL =BULLET>
<LI>Throttle position
<LI>Brake state (The brake must be applied to activate grade braking)
<LI>Vehicle acceleration/deceleration
<LI>Grade/Load
<LI>Vehicle speed </LI>[/list]


The determination of the PRNDL position is made by a logic subsystem. Several factors are calculated and weighted and then a sum is calculated. When this calculated sum surpasses a threshold, a PRNDL override is commanded.





The following charts provide the maximum Pre-Select (manual) shift points:






<TABLE width="100%" border=1><A name=tab2-944861><A href="file:///C:/DATA/archieves/2001%20Silverado%20info/New%20Product%20Information%20-%20Grade%20Brake%20Feature%20of%20Allison%201000%20Series%20Transmission%20%2302-07-30-004A.htm#tab2-944861" target="_blank">
<H4>6.6L Diesel Engine (RPO LB7) with 3.73 axle ratio</H4></A>
<T>
<TR>
<TH vAlign=bottom align=middle>


Shift</TH>
<TH vAlign=bottom align=middle>


Transmission OSS RPM</TH></TR>
<TR>
<TD vAlign=center align=middle>


5-4</TD>
<TD vAlign=center align=middle>


4017</TD></TR>
<TR>
<TD vAlign=center align=middle>


4-3</TD>
<TD vAlign=center align=middle>


2832</TD></TR>
<TR>
<TD vAlign=center align=middle>


3-2</TD>
<TD vAlign=center align=middle>


2196</TD></TR>
<TR>
<TD vAlign=center align=middle>


2-1</TD>
<TD vAlign=center align=middle>


1214</TD></TR></T></TABLE>






<H4>Important</H4>


Grade Braking is not intended to reduce the need for great care by the driver when driving a heavily loaded vehicle down a grade. Drivers should continue to take all normal and appropriate actions to keep the vehicle under control at all times.




  1. <LI =1>Does grade-braking feature work on level roadways while trailing or hauling heavy loads and applying brakes? The feature is actively calculating whether or not to command a downshift while on level roadways, but it is much less likely that it will command a downshift under these conditions. The reason is that the Transmission Control Module (TCM) is using vehicle acceleration/deceleration as a determining factor. Since the vehicle is more likely to respond to vehicle brakes on level surfaces vs on a grade, grade braking is less likely to command a downshift.
    <LI =1>Does grade-braking work in Tow/Haul and normal mode? Yes, grade-braking is active in either mode.
    <LI =1>Can I turn grade-braking off? No, automatic grade-braking is always an active part of the transmission control system.
    <LI =1>Does Tow/Haul have to be selected? No. In normal mode, the grade-braking feature will pre-select only the 5-4 downshift, whereas in Tow/Haul mode, grade-braking has ability to select the 5-4, 4-3, 3-2 downshifts.
    <LI =1>When will I get a grade-braking downshift? There is no "fixed" shift point for a grade-braking downshift, however, the grade-braking downshift will never occur such that the engine speed following the shift exceeds GM Truck guidelines. Also, the grade-braking downshift will never occur without depressing the brake pedal.
    <LI =1>To which gear will grade-braking downshift in each mode? The downshift will always be to the next lower range, i.e.; it will not "skip" ra
 

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Great post except for using the word "algorithm". The first thing they teach in a creative writing class it to write everything on a ninth grade level so no one gets left behind.
Later! Frank
 

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Frank Blum wrote:


"The first thing they teach in a creative writing class it to write everything on a ninth grade level so no one gets left behind."


Frank,


I'm with ya, but mine taught me sixth grade level. Those classes must be geared to be student specific!





 

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Pick, Here is a simple answer to your question: In normal mode the torque converter is unlocked in 1st, 2nd & 3rd. It is always locked in 4th and 5th. In tow haul the converter is unlocked in 1st, may or may not be locked in 2nd and always locked in 3rd, 4th and 5th. In Tow/Haul/Race the shift points are higher and firmer. Later! Frank Edited by: Frank Blum
 

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NWDmax said:
Only dumb questions are those that are not asked.


...................[UNQUOTE=NWDMAX]


Disagree ~ dumb questions are those which one can't understand the ans. My missus can ask questions a mile a minute and can't understand ans. Whats the use?
 

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algorithm...

style of dance coined by a certain vice president
 

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Hoot ...
... Jim
 

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How much of a decrease in MPG would you see if you ran T/H a majority of the time???
 
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