6 speed not updating current gear fast enough

Js95gt

Js95gt

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Dec 4, 2010
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Walker, LA
After my track outing today, I have found that the current gear is not updating quick enough after a shift. It is making rpms go north of 4200rpm because it will not command the next gear change until the current gear is updated. I am going to include a tune file and a snapshot of the log. Tune is basically stock with WOT shift points set way low trying to get a gear change. Anybody run across this before?
 

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hondarider552

hondarider552

Getting faster
May 28, 2008
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What happens when you load a bone stock TCM tune in, does it shift? What shift is this happening on?


Way back when I used to mess with shift points on my LBZ, I used to change both the shift MPH and shift speed, but found it to hang the shift every now and then, so I only started to mod the shift RPM. I never had any problems after that. I do DO NOT touch torque limiting. I do not belive in messing with it and I have proven to myself it's not needed. I ran great times on bone stock TCM files.
 
mike diesel

mike diesel

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Sep 6, 2012
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Who built the trans? Allison will shoot past the targeted shift RPM to an extent. But if the shift point is set low and it's hitting 4200rpm before shifting, then you may have cooked clutches, torn apply pistons or low fluid.
 
hondarider552

hondarider552

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May 28, 2008
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ok just saw you log.

I had a similar issue. Load a stock TCM tune in the truck. If it still hangs the shift I bet you have a trans apply piston issue. I tore the apply piston for C4 in my GMC on the 1-2 shift and Mike L had never seen that failure before. I don't necessarily think that is your issue, but not out of the question especially on a 2-3 shift.
 
Js95gt

Js95gt

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I'll try a bone stock tune to see. I'm going to flash it with my tech2. I believe this to be software related due to the fact that it is waiting for the TCM to update current gear before commanding the next. I have a BT lockup box and locking it at the top of 1st gear. It's not just a normal overshoot, it's a very late command due to current gear not updating fast enough.

I built the trans myself.
 
hondarider552

hondarider552

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May 28, 2008
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Log your commanded gear with efi.. vs current gear...


You will see right away if it's trans related or tune related.
 
THEFERMANATOR

THEFERMANATOR

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Feb 16, 2009
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How much time is taking place between the time it shifts, and the time it updates the gear? I know it can take over a second for the TCM to verify the trans has changed gears and setup the shift solenoids for the next shift, then updates the current gear.
 
Js95gt

Js95gt

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Dec 4, 2010
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Walker, LA
It's a hair over 1 sec. So what are the fast Allison guys doing to get it to shift fast enough in the lower gears? I guess I could spin the motor up higher, just doesn't make a ton of power up there. I have the fuel limit set at 4200 to cut some and 4600 is 0mm3 right now and it shifts 2-3 around 4400. Maybe do less gear?
 
mike diesel

mike diesel

I'm alright.
Sep 6, 2012
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I command my 2-3 shift at 3800rpm, it shifts within 50-100 rpm of that no problem everytime. And mine clicks shifts off very fast.

Did you try the stock tcm tune yet to see if it's a tuning issue or a trans issue?
 
Js95gt

Js95gt

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Dec 4, 2010
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Walker, LA
Mine will make the shift within 100rpm of command, but won't command the next shift until the current is updated.

I'm going to flash it back to 100% stock with the tech2 later today and will try it this evening.

Thanks for the help guys!
 
Js95gt

Js95gt

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Dec 4, 2010
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Walker, LA
I'm pretty good with them normally, but this is my own, so... Lol

I really don't think it's internal. Will try flashing stock in a bit to see. Just real busy in the shop at the moment.
 
Js95gt

Js95gt

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Dec 4, 2010
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Walker, LA
So, stock flash didn't help it any. I logged a LMM I have here and from the time the shift is complete to the time it shows current gear update, is about half the time of mine. Shift is clean and not drawn out at all. Really don't think this is in the trans. Thinking I may need to swap TCM and see what it does.
 
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