Q: Car won't shift

Hi there. If your Blazer is moving but just will not shift, then it is not the master cylinder. If the Blazer will not move at all then the brakes may be locked up, which can be caused by a failing master cylinder. If the transmission will not shift out of first, but will move, then you may have low fluid or possibly a valve body problem in the transmission. It can even be the first sign of needing the transmission rebuilt. Start by checking the fluid. If it is dark or smells burnt, then there is an internal issue. I would then remove the transmission pan and inspect the inside of the transmission for metal which would indicate an internal problem. If you need further assistance, I recommend you have a mechanic, like one from YourMechanic, inspect for possible transmission fluid leaks and replace any damaged parts.