It has no air in it, DHX 5 are rubbish in the fact that if you have no air you have no adjustments.

If you run a shock with no air you will basically only be using the spring. You will have no damping or control over how fast the shock rebounds.

Cant you just pump some air into it? or is it like the silly dhx's you got on SX trails that dont allow you to put air in them?

Interesting.

Anyway, put 150psi in you shock - minimum, this will avoid oil cavitation.  The bottom out adjuster will not change the rebound speed.  Take the shock off the frame, take the spring off, leave 150psi in.  Turn the rebound control to minimum, the shock should push and and return from the shock body smoothly in both directions.  It may be that the shock has been custom tuned for a higher weight spring than you now have so it will be really slow on a lighter spring.  My DHX5's are custom tuned to run veeeeeeeerrrrrrrryyyyyyyyyy slow rebound.

If the shaft doesn't move smoothly or gets stuck down in the body, a service is required as your seals/oil may be knackered.

Anyone know how to rebuild one of these shocks???

Set the air pressure to the min (70-80psi) first then set the rebound.

And they are so simple to take apart and put back together. The only hard part is clamping the main shaft to unscrew the rebound end off it.