Chevy & GMC Vans

okay i know this is not an astro but this is serious: it is a 1989 chevy k-1500 ext. cab. 4 wheel drive with the 350 v-8 it is a z-71 truck. here is the problem when cold there is no adnormal noises but when warmed up it seems to be making a knocking noise a idle when in gear with foot on brake but in park there is no knocking noise when rev there is no knocking noise.

Could be a broken flywheel.

here is more info. when i slowly brake to a stop there is no knock when i push the gas very little i feel the trans and engine shift back it then sounds like a knock also if i brake fast i feel the same thing but it feels like it shifts forward. weird.

bad motor or trans mount? :-k

umm.. torque convertor issue? out of balance? :-k

something to do with a real bad u-joint on the front shaft? :-k

sorry that's all i gots

I like Rob's first suggestion, check the motor mounts first thing