(909) 838-4587 ed [at] le-suspension.com

The top two pistons are common aftermarket pistons. The bottom two are common stock pistons. The left are compression pistons and the right are rebound pistons.

The working holes are the smaller sets. When oil is moving one way through one set of small holes it is also moving past the other piston through the larger holes.

There is a shim stack that controls the flow of oil through the small holes. The larger holes, along with a spring and shim form a one way valve. AKA a check valve.

If you have not already done so, now is a good time to read:

How Your Cartridge Forks Work

The working holes look small but they only need to flow more oil than is being displaced by the cartridge rod. The check valve holes are larger because there is space to make them larger and to insure that only the other piston is doing work.

Can’t see any difference that matters? Exactly. The shim stack does the work. The piston just holds the shim stack. It’s the same in your shock.