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Chevy Blazer Won't Shift

Q. Hello, my name is Kevin from Ohio. I have a question in reference to my 1977 Chevy Blazer 4X4 automatic transmission with a 350 small block engine. The engine is not fuel injection. This may sound a little funny, but I'll give it a whirl. I recently replaced the headers to my truck, because they were very old and rusty.

My truck ran fine before working on it, and shifted normally (other than the rusted and loud exhaust). I had a hard time getting the old exhaust pipes off underneath the truck. I banged some stuff around underneath the truck trying to get the pipes off. I successfully got the olds pipes off, and just started up my truck.

I took my truck around the block and noticed that the transmission would shift automatically into second or third gear. I had to manually shift the truck using the shifter on the neck of the steering wheel. The truck would shift, however only by doing it manually.

I then took my truck to get the muffler's replaced. I asked the muffler technician if I could of possibly knocked something off underneath the truck, causing it to do this. The muffler technician advised me that I could of possibly knocked off an air hose to the transmission causing it not to shift automatically.

I've gotten underneath my truck and could not locate anything out of the ordinary. As you can probably tell, I'm not very good at working on vehicles, or writing letters. I was just wondering if you have ever heard of such a thing, or if you think I should just take it to a transmission mechanic. If you could respond with your answer at your convenience, I would appreciate it.

Thanks for your time.
Kevin

A. There is a vacuum line that goes from the intake manifold down to the transmission to control shifting. It's very possible that you knocked it off. Get it looked at if you can't find anything yourself.

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