89 with knocking sound coming from transmission
 

I have a 1989 Silverado with a 350 engine and auto transmission.

The problem I am having is at idle there is a loud knock coming from the transmission. If I raise the RPM's about 200 it will stop making the noise. It makes this noise in all gears including park until I give it a little gas and then it is very quite.

I am thinking a valve my be stuck.

Any ideas?????

That knock you're hearing isn't coming from the transmission, but rather the engine crankshaft.

The thrust bearing is worn to the point that it's letting the crank move fore and aft enough to allow a throw to hit the block.

Allan