Tranny is wigging out on me, I sure hope someone can help me.I don't have an f-body but at least it's a bowtie, my 96 4x4, 4l60e, blazer will shift fine to 45mph then the speedo will begin to go down and naturally the tranny shifts up. The speedo will go down to 35 and stay no matter how fast I am going,the rpms keep climbing, but no shift. I checked the trans. speed sensor by pulling off the harness and it acted as it should, no shift at all. It did it a few months ago for about 2 minutes and then quit, now its raised its ugly head again and doesn't seem to want to go away. Anyone got any ideas.

 

Dont have an answer for ya, but you might want to ask here: www.chevytalk.com

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Ya can't have too many fast Chevys!

 

Sorry but I doubt we will be able to actually tell you what it is here. I have seen instances of poor grounds causing erratic operation of various segnals, including speedo. It is definately not the tranny of course. I would concentrate on checking the speed sensor but more likely the circuits feeding it. You will need someone with a wiring diagram and a good meter such as a Snap-On Vantage.

One other note, likely not related to your problem but just as important. These specific year trucks have an internal ground problem IN the VCM. You do not have to replace it to fix it though. Some of the 1996 4L60Es have the jumper wire from the factory. The best way to tell is flip the bale on the VCM, turn it over, and disconnect the red connector. Now see if there is a wire in the #26 cavity, it is next to 2 yellow wires. If there is a black wire in the cavity, it's OK. If not install the jumper harness #12167310.

 

Thanks CHVYPWR and transfixleo for the advise. I'll definelately check the VCM, thanks for the info.