Here's the story,

Since I switched my 305 for a 355 I ordered a new clutch (which was professionnaly made) with a steel clutch disc and a HD pressure plate. The T-5 tranny shifts fine in all gears, but here's the problem.

Let's say I'm driving at 2500 RPM, I take my foot off the throttle pedal and let the engine rev down on it's own, around 1600 to 500 RPM I'm getting big knocks, like huge hesitations coming from (at least it looks like and feels like) the tranny...

Just like I would get in gear and I'd drop it in 1st too fast without giving it enough gas. I can actually feel it in the shifter and I can see it move about 1/2 inch up and down as the knocks are felt.

What could do this?? could it be a tranny mount? or a tired engine mount?

Yes I did put in a NEW Pilot clutch bearing in the crank.
Thanks for ANY help!

 

If the shifter is moving, you need a trans mount, regardless of any other symptoms.

Get an Energy Suspension one and see if the rest of it improves too.