Allison finally fixed!

[tim975]

Hello everyone!

I've noticed a few of you guys have had problems with your Allison transmission surging and lurching. I've had this problem since I bought the truck 3 months and 9500 miles ago. Last Monday the wife took the truck to work, coming home she said it made a whining and grinding sound and SES light came on. I took it for a ride, did nothing for me, but light stayed on. Took it to the dealership where I bought it, that was a waste of time. So I took it to the dealership outside of town, they put the computer on it, transmission code came up. (don't know the code, I'll try to find out tomorrow). They found the NBSU (pressure?) Switch out of calibration. They installed a new switch (FP #29540479, Switch Kit 4.054). Now it runs great! No surging or lurching. Next time you make a trip to the dealership, mention this to them, maybe this could be your problem as well. Good luck to you all!

Tim975

2001 Chevy 2500HD LS Reg Cab LB D/A
7 1/2 Western Pro Plow

[DieselDennis]

So is the surge a Neutral Backup Selector Unit malfunction in the transmission? Or has your truck just not surged again? Seems by what I've been reading there is no rythm or cause for this behavior. Has anyone been able to produce it on demand?
So is it an engine deal or a transmission quirk? Or possibly a disagreement in what one tells the other one to do?

[NutNbutGMC]

Quote:
They found the NBSU (pressure?) Switch out of calibration. They installed a new switch (FP #29540479, Switch Kit 4.054). Now it runs great! No surging or lurching.
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Quote:
So is the surge a Neutral Backup Selector Unit malfunction in the transmission?
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:confused:

[tim975]

Hey guys!

You'lll have to bear with me as this is my first diesel and I'm still learning about the truck and the electronic stuff. I just talked to the gentleman that worked on my truck, he said that the NBSU Switch has been malfunctioning on a lot of the Allison transmissions, and that GM has redesigned the switch, that's been the problem for a lot of people. He called his technical assistance people, they told him to try that first. He said the switch is mounted on the outside of the tranny, and that it was part of the transmission, not the engine. That was all he did with the tranny, because I drove it around town last night, stop and go, testing it out, and I didn't feel anything anymore. He said that must have been what it was. If I can duplicate the problem or get more info on it, I'll definitely keep you guys posted. I hope I wasn't too vague.

Tim975

2001 Chevy 2500HD LS Reg Cab LB D/A
7 1/2 Western Pro Plow