I have a 71 C4 paired with a 351C in my 68 Coupe. Today it started making a grinding noise when putting it in park. Recently changed the transmission filter and gasket and all looked well. It shifts fine between all of the other gears. Just makes the grinding when putting in park.

Anyone had this happen? Have any ideas what the issue might be and how to correct it?

 

You might check the flexplate and converter for tightness and/or cracks...

but,,,, I want to make a guess, a guess that is totally general in nature, but the odds say I will be right.

You recently changed the filter and gasket, which is what most people do when they notice a "change" in their transmission.

For this reason, MOST of the time, the filter change comes either right before or right after a transmission failure.

My guess is that your C-4 is toast, and it will need to be repaired or rebuilt. 99.9% of the time, once a transmission starts slipping, skipping, or bitching (making noise), the new filter and fluid ain't going to help.

 

I'll check the flexplate and converter, thanks for the advice on that.

As far as changing the fluid and filter, that was strictly routine maintenance. The transmission functioned perfectly prior to the change, no indication of a problem. In addition, the fluid was still pinkinsh/purple as it should have been rather than the brown that is typically an indication of issues. There wasn't any metal flake in the pan or filter to indicate issues either.