Allison Gear Indicator

gr8wing · November 30, 2006

I have a 2001 4WD 2500HD 8.1/Allison. We just had a huge snow storm and I have been out in it quite a bit. It started acting funny in the second day of the snow. The gear indicator would be showing different gears or not a gear at all. The cruise control quit working, it started shifting funny and now falls on its face under hard acceleration. These may have started all at the same time or have started as I noticed them. Today with the snow gone on the freeway, I had taken it out of 4wd and the cruise still didn't work and at one point it downshifted and I had lost most of my power and had to pull off. I have also noticed that the fuel guage is fluctuating under acceleration and decel. this is also new.

I would think that this would be somekind of a ground problem or an electrical connection issue. I am hoping that someone else has seen this or has an idea of what i should look for.

Thanks in advance for any help.

GM-Tech · November 30, 2006

The gear indicator problem sounds like a bad neutral switch on the trans. LOTS of problems with those and there is a new design switch out for that problem. They tend to get water inside due to the fact that the left front tire throws water right on 'em when you turn left.

I don't think the other problems are related, but they could be (the cruise almost definitely), so I'd replace the switch and go from there.

The part number I have for the switch is 12450016. That may have changed.

Note that when you replace the switch, you need to take a file and knock off any mushrooming or burrs on the shaft it slides over or you'll damage the new switch when you put it on.

gr8wing · December 2, 2006

Well, finding one of those Neutral Safety Switches is easier said than done. I checked with most of the dealers in my area and I just get laughed at. They are backordered, they are a BIG problem and it appears that it is a huge problem in the snow. Not sure what to do now, my tranny is getting really weird in the shifting if it will shift at all. I just got back from the dump about 15 miles away and the entire trip back it stayed in one gear, maybe 2nd or 3rd, but it rev limited me to 45 MPH. The RPM's were not bad, but I think the computer thinks that I am in a different gear than I really am. I hope this is all the same problem, but it seems I will not know until I get that switch and my truck is going to be useless until then.

My kingdom for a switch!!