Fox CTD not working? It may be fine!

We get a lot of people through the door complaining that their brand new Fox shock, or more specifically the CTD function on it is not working, though in some cases it’s doing exactly what it is supposed to.

What exactly is the CTD function?

CTD stands for Climb, Trail and Descend and it is compression damping, not “lockout”. In fact all those controls that say “lockout” on them are nothing more than compression damping controls that you can turn up full and by full I mean closed.

Imagine that the damping on your shock or fork is a tap, the more close it, the more you restrict the flow of oil. Restricting that flow of oil (both on compression and rebound) is what ensures that your bike doesn’t handle like a pogo stick. The climb position is the most closed position, descend the most open.

Mine definitely isn’t working, it’s nothing like my friend’s shock which does lock out.

You can have two seemingly identical shocks but that doesn’t necessarily mean that they are set up to behave in the same way. Fox shocks are very tune-able in so many ways, they aren’t really a stock item and a bike manufacturer will specify a specific tune to suit their frame. The following can affect compression damping:

  • The tune on your shock – this is controlled by the shim stack, something that for the most part the home mechanic cannot change the necessary parts aren’t available and the tooling necessary is cost prohibitive. The tune is often indicated by either a letter – F, M or L (firm, medium or light) or some Fox shocks have a little graph with one of three positions highlighted. Blue is compression, red is rebound.
  • The spring curve on your frame – the design of your frame dramatically affect how quickly the shock progresses through it’s travel and how much leverage you can exert on your shock when you compress it. For example an Orange Five or an Empire will have a dramatically different spring curve than that of a Trek Session.

So as you can see you can’t really compare two different CTD shocks unless they are on the same model of bike and have the same tune.

So can I change the tune?

Yes many suspension repair centres including ourselves can change the tune of your shock during a service.

But the CTD on my shock used to be much firmer and now it’s all over the place!

If you have noted a sudden change in performance then chances are that there has been a leak somewhere in the damping circuit. You won’t be able to fix this yourself and an air can service won’t help. You need to take it to a service centre.

Can you change the tune on my Fox Shock without me having to pay for a service?

No I’m afraid not, to change the tune on your shock you have to completely strip it down, drain the oil and nitrogen etc. You couldn’t put it back together without cleaning it and changing the seals, so basically you have to service it.


Just because your CTD shock doesn’t lock out completely it doesn’t necessarily mean anything is wrong, though it may not be performing at it’s best. Air in the damper fluid, loss of nitrogen pressure, corroded internals or a blown damper seal are all possibilities however none of these issues can be fixed at home. Thankfully warranty issues appear to be very rare, the majority of failures we see are due to a lack of maintenance.

CTD not working, Fox rear shock service, Fox nitrogen charging
Part of the metering rod assembly from a poorly/unmaintained Fox CTD, note the corroded tip and the fact that material has begun to break away.

If you believe your Fox CTD isn’t working please feel free to call in to the workshop or call us, we will be more than happy to talk you through your issue. We don’t charge for advice, if we tell you that your shock is doing what it should be it will only cost you your time. :)

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