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Question for trans guru's

SFC Cobb

SFC Cobb

Jesus Freak
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Location
Hurst, TX
Sometimes when slowing down to stop I get down to around 10 mph or so the trans does a sudden down shift and it is a hard shift.

At about 260,000 mile (15K miles ago) the NSBU went out and it seems to me that it was doing this samething when that happened.

Is the hard sudden downshift one of the things that happens when the NSBU fails or is it something else going on? Like failing clutches or a bad valve body?

IIRC the hard shifts stopped after replacing the NSBU.
 
My tranny will occasionally do something like that after I dramatically change tunes. It almost feels like I have been tapped in the back another vehicle. I would guess that it is pressure related, but do not know for certain.
 
I have the same thing happen a few times. Almost like the trans is confused as to what gear to be in. Mine usually happens about 3-4 miles after first start up, but has happened in places like parking lots where I'm on the gas and let off a lot.
 
The only times I've had that happen (this is my 3rd Allison) is when going downhill and only to 1st gear. I believe it's normal.
 
When pulling my camper in TH sometimes the 2-1 shift was noticeable to say the least, but not every time and not dependent on flat land or a grade. I just took it as the braking in TH.
 
Mine has done that a few times in the past also... when it happened, it was always during hard braking almost near a complete stop, passing through 10mph. I could tell it was shifting into 1st, but yeah it feels like you're being rear-ended when it happens.
 
saratoga said:
Mine has done that a few times in the past also... when it happened, it was always during hard braking almost near a complete stop, passing through 10mph. I could tell it was shifting into 1st, but yeah it feels like you're being rear-ended when it happens.
Click to expand...

That is a good description of what happens.

I wonder if it is connected with driving slow like around town and sudden braking and the trans reprograms itself.
 
At first I thought it was the sticking yoke problem like my 01 1500 :mad2:had until I remembered that the 1500 did that at when it came to a dead stop. The feel is about the same except that this is when the alli shifts to first while still slowing down and it was usually right after hard braking like on an exit ramp. Haven't noticed it in a while but as bad as my tranny was slipping lately it probably did not have enough bite left to grab that hard:nonod::D.
 
Local tranny shop ran by a guy well known in the racing industry now into funny cars and dragsters. He is the go to guy here around Lafayette. I already had the hard parts from suncoast but after thinking about it, I decided to let someone with experience do it instead of halfassing it myself. I ordered a suncoast stage 3 for $2583 (shipping was almost $100) and the shop fee is $1500. He said he knows the allison well and has a few extra things he adds to the rebuild that he did not care to share. It comes with a 12 month, unlimited mileage, unconditional, warranty. He assured me that when he is done, the alli will outlast the stock engine internals. I could have had it done cheaper but I plan to keep the truck for a long time. The hotrodders around here have nothing but high regards for his work. After talking with a few guy's that have been to him before I have no doubt that I made the right decision.
 
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