Allison 5sp: No engagement

Mpsoldier

Mpsoldier

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Mar 10, 2010
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posting up for a friend i couldnt think of anything when i heard it doing this, so here it goes.
Transmission will not engage in any gear after having it rebuilt ppe stage 4 kit went in it.
new nsbu switch also and solenoids
new harness in trans
i reset the taps and also monitored the input speed and gear selector when you monitor the gears from actually to desired any gear other than park it goes into neutral. also when you unplug the harness to the trans it doesn't change anything still no reverse and or drive.
input is about the same as idle rpm
last there is zero codes or shift inhibitor lights. only code is a glow plug code.
new filters and fluid also topped off.
thanks for any help of ideas to test as i really don't have time to mess around with it.
 
Robby Avery

Robby Avery

GM TECH @ FENDER GMC
Jul 31, 2008
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Have you check every connection like tcm and ECM connections to make sure all are tight? Just a thought check fuses as well just make sure nothing blown would like to know what y'all find out sub'd
 
Mpsoldier

Mpsoldier

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gm tech side job works for a great dealership guy knows his shit to but hasn't seen this before. I feel its electrical somewhere or possible something in valve body not applying pressure.
 
Mike L.

Mike L.

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Aug 12, 2006
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Pull plug at bell housing and start it up for a second and see if fluid gushes out. Usually no pressure will throw a P0701/702 code. This will happen if bell housing gaskets are reversed.
 
IOWA LLY

IOWA LLY

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Feb 23, 2007
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Mpsoldier said:
gm tech side job works for a great dealership guy knows his shit to but hasn't seen this before. I feel its electrical somewhere or possible something in valve body not applying pressure.
Click to expand...

He knows his shit but is stumped as soon as the computer won't tell him what's wrong.....:rolleyes:




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Mpsoldier

Mpsoldier

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Thing is the computer tells you so much what's wrong he's not going to work on the truck when all he was payed to do was assembly of the transmission. As far as the kit and build it was just clutches so I really can't Blair the guy from joy wanting to much to do with it especially when my buddy gave him a unknown condition trans to have him build it up on.
 
IOWA LLY

IOWA LLY

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Feb 23, 2007
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So you said he already tried unhooking the harness at the back of the trans and it still had no forward or reverse gears correct? I just want to clarify that this test has been performed before we move on.
 
Mpsoldier

Mpsoldier

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Mar 10, 2010
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Yes that has been performed harness has been checked and double check connectors have been cleaned and nsbu switch is brand new transfer case still engages to 4lo and 4 high so it's not that either
 
IOWA LLY

IOWA LLY

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Manual valve pin fall out? Pull pan and verify that its in there.



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IOWA LLY

IOWA LLY

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If he is unplugging the harness and it still won't give him any gears, (should give him 3rd and reverse) I don't care about limp mode or codes. He has a mechanical issue inside the trans. And since we know the pump is drawing and pumping fluid we can rule out a few things.

Best way to diagnose anything is start with the basics. No need to diagnose the electrical side of things until the trans will at least give him 3rd and reverse through hydraulic default.

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