Some of the Monarch RT3’s come with a reasonably stiff lockout when new but a lot of them don’t stay that way for long. Here’s why that happens and what can be done about it.
Once you open up the damper of the shock, this is what you find. You have a piston just like any other with both piston faces covered by shims for oil braking in the rebound and compression directions.
It gets more interesting when you take the piston off and see the shaft.
Inside this shaft are a few things. A rebound needle, and shimmed compression adjustment poppet that’s also spring loaded. The compression poppet assembly can be seen here:
In the top row you can see the normal arrangement of parts that make up the compression poppet valve which resides inside the shaft of the shock. Flicking the lockout lever engages a cam, which pushes a rod (not shown here), which in turn preloads the shimmed blue poppet (pictured to the right of the small poppet spring). The poppet has 2 shims which provide a smoother transition between low speed to mid speed shaft movements. To the right of the blue shimmed poppet, you see a red washer, then a white backup ring, then another red washer. Herein lies the problem.
Anytime you have a lockout shock or any shock that has a pedalling platform, it’s very important to control the amount of oil flow from one side of the piston to the other. Leaks from one side to the other will nullify the function of any lockout. In this design, the oil flow can be broken down into 2 modes. Oil flow through the piston itself and oil flow through the centre of the shaft. When the shock is unlocked, oil flows through both the piston and as well as inside the shaft, bypassing the piston. When the lockout lever is engaged, the bypass (inside the shaft) should be choked off, thus leaving only the oil flow going through the piston itself (which in this case should be fairly stiffly valved). The centre oil flow choke is what fails to happened once this shock gets some use. The bypass leaks as a result of Rockshox using a white backup ring as a seal. You can see it in the picture above between the two red washers. The solution comes when we replace the red washers and white backup ring with an o-ring seal complete with its own precision carrier (the silver part with o-ring in the picture above). This part eliminates the leak that develops through the white backup ring. For customers that want a very firm pedalling platform, I replace the blue poppet entirely with a poppet that has a slightly different needle profile to keep leaks to an absolute minimum.