1981 Other Chevrolet Models Transmission

Transmission problem
1981 Other Chevrolet Models V8 Two Wheel Drive Automatic

I was just getting on the interstate I started to get up to speed then had to hit my breaks really hard to avoid getting in an accident. After that the trasmission wouldn't shift passed 2nd gear what could be the cause of the problem or fix. The engine is a 350 V-8 the transmission was bought by magdog transmissions in Florida and was a rebuilt transmission a few years ago the truck sat about 2 years and was only driven on for 500 miles.