Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Enter your ride HERE to be a part of this months Ride of the Month Challenge!

1 - 20 of 21 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter · #1 ·
Hello everyone again. I have a question about my allison transmisson. I have had this truck for about 2 weeks. Everything has been alright untill today. We got about 13" of snow yesterday and I went out and drove the truck for about 60 miles and everything was going good. I get back to town and stop at a red light and go to take off and it felt like the rear tires spun then caught. After that the truck would only get up to about 30mph and it felt like it was starving for fuel. at the next light I put it in N and reved it up and it reved right up no problems. I put it back in gear and it sat for a second and popped itself out and it said range selection not avalible or something like that. It still won't run right. Anybody have any thoughts? Thanks in advance for any help.
Lee
 

·
Hi, I'm Earth. Have we met?
Joined
·
3,162 Posts
Sounds like you might have gotten some snow in the nutral safety switch (NSBU) Can cause some weird problems like that, DOse you PRND321 on the dash do anything weird?
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #3 ·
I looked under the truck when I got home and it did have some snow packed underneath. While I sat at the red light I put it in N and reved it put back in Drive and it kinda kicked out of gear. The instrument panel had a message that said gear selection not allowed or some thing to that effect. So I put back in N then put it back in Drive and it stayed but will not get up to speed. It's running like someone is choking it to death.
 

·
Hi, I'm Earth. Have we met?
Joined
·
3,162 Posts
WHat dose it do after you shut the truck off for a few min.? Dose it shift gears or is it stuck in one gear and limited to 2000rpms?
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #5 ·
I have it in the garage right now trying to melt the snow off. But before I did that I shut it down and waited like a minute and started it up and it did the same thing.
 

·
Hi, I'm Earth. Have we met?
Joined
·
3,162 Posts
Sounds like a bad (NSBU) to me! WHat about the shifting, would it shift gears and rev beyond 2000 rpms in gear?
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #7 ·
No it didn't want to shift. it ran up to about 2500 rpm and it felt like a Pro stock tractor getting under the turbo. Real fluttery sounding.
 

·
Hi, I'm Earth. Have we met?
Joined
·
3,162 Posts
Any Check engine lights? Is there any chance your fuel is gelled up?
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #9 ·
I didn't notice any lights. We have blended fuel here plus I use power service fuel additive just in case.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #10 ·
How much are those NSBU ?
 

·
Registered
Joined
·
484 Posts
$50 at the Allison dealer, get it from them not a GM dealer, GM dealer will put you over the counter and charge you 3 times that, and not even give you a free tube of vasaline.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #13 ·
Do this things usally go bad? nsbu thingys
 

·
Registered
Joined
·
3,023 Posts
I think the guys hit it right on the diagnosis, NSBU switch. You are probably taking off in 3rd gear and that's why it feels underpowered. Buy the switch from an Allison dealer and if you're going to install it yourself let us know as there is a correct procedure to do this.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #15 ·
Could this be under a GM recall? Truck only has 46000 miles. I might run it in and see.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #17 ·
I had it in the garage and got it dried up. I took it for a spin and the truck ran perfect again. Is the (nsbu) hooked in with the shift linkage? If so that was where I had alot of snow packed in.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #19 ·
I have been doing some research and it sounds like they have an updated version and someone makes a cover to protect it. It is going into a LIMP mode. So now I need to see if it has a GM recall notice. I really don't want to pay for it.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #20 ·
Took the truck in today. They said there weren't any codes so the checked the vacuum on the fuel system and said it was high so they put a new fuel filter on and it checked out ok. Sound right to you guys?
 
1 - 20 of 21 Posts
Top