1984 vf750 rear shock problem.............rebound to up position

the rear shock on this bike has no rebound,,push it down and it stays down...is it supposed to have a rebound built into it..a little ait pressure helps and i have the damping setting on #1..im only 120lbs..checked the linkage and it seems free .i can lift it up to raise the rear end but push it down and it stay........smmmmmmmm.looks like a shock problem..any suggestions.

.got the front forks working someone used a heavier oil than trans fluid ..works like its sposed to now,,but the rear is screwy..thanks gregg in ohio with a new bike in the stable..

 

well i pulled the rear shock and checked all the suspension linkage al is free ..found a used vf750f shock on ebay..the one that i pulled out was already replaced had that yellow salvage writing on it ..once it was compressed it stayed down un less u put max air in it then it worked like a airshock but hard as a rock..figured the shock was shot..we will try to use another one..gregg