I have a C4 Auto in my 67. Car shifts great from gear to gear, never had any issues when running. The last few weeks, on 3 separate occasions, after starting the car, when I put my foot on the brake and shift from park to any gear, it does nothing. I can go all the way down with the shift lever to D1 and it doesn't get into gear until I go back to park and then try again. Any ideas? Only 3 times it has done this, but all within the past few weeks. When not doing this, it works great...

Also, I have noticed that if I'm trolling along in very slow traffic (5-10MPH), when I let off the gas to just sort of drift with the slow traffic, I hear a "thunk" that seems to be either coming from underneath or the rear end as soon as I let off the gas. I then can hit the gas and it accelerated fine and all and doesn't seem to be slipping or anything whatsoever, but if I'm going along in slow ( almonst stopeed) traffic, it "thunks" when I let off the gas. This might be nothing at all to worry about, not sure.

I am hoping these 2 things are simple...trannys scare me.

 

Start with the simple things. Check your vacuum line going to the modulator. If that has is split or is broken it will make your trans do some funny things.