Just wondering how often people have their shocks rebuilt. I bought a used frame with an fox rc4 and was wondering if I should have it rebuilt just to be sure or wait till something is not acting right. How would I even tell if the shock needs a rebuild in the first place. Are there any obvious signs to look for.
Different manufacturers have somewhat different service intervals, and different models of forks/shocks and different riding styles also have an effect. For a coil shock, the service interval is typically 100-150 hours of riding, or once per year. If the frame you bought had a solid season of downhilling on it, it is definitely a good idea to send the shock out for a service. I would also recommend spending the bit of extra money to have it custom tuned to your weight, bike and riding style while it is out.
Forks and air sprung rear shocks typically require a basic service (similar to an oil change on your car) every 30-50 hours of riding. Then typically in the 100-150 hour area, any fork or shock should get a complete tear down (similar to a complete engine rebuild on your car). As previously stated, these figures can vary quite a bit depending on the riding discipline and conditions.
It is best advised that you get the suspension serviced before anything actually goes wrong with it. For starters, the performance of the suspension will degrade well before you notice any actual problems. Furthermore, regular maintenance will prevent damage to the critical parts. I have seen many expensive fork crown steerer assemblies have to get replace due to lack of basic maintenance. Otherwise, it is a good idea to send away, or at least take it to a shop which is competent with suspension, when you notice anything slightly awry. Usually the first indication with a rear shock is when the damper starts to make a slurping sound, or exhibits noticeable friction. But again, at this point the shock will have been overdue for service.
Forum discussion here: https://www.ridingfeelsgood.com/topic/when-to-rebuild-shocks/