I’m curious as to how the brain should react when I sprint hard, out of the saddle. I notice I get a good amount of bob when really cranking the pedals. However, when climbing seated and hard, the brain seems to work well and keep the rear relatively stiff. The bike is a 2011 Epic Carbon Comp but does not have the hours or miles on it to warrant brain service yet and there doesn’t seem to be any leaking from the brain or the shock. The shock is inflated correctly by my LBS as well.
The Brain uses a brass weighted valve to control the opening in the shock. It is intended to remain “closed” until the rear tire hits a bump that causes the axle to lift upwards. The weight of the Brain valve resists the motion initially and leads to the “opening” of the valving, that allows the suspension to compress. (That’s a short summary. I can find a video if you want to know more.)
That design is meant to recognize the difference between bump forces (upward direction) and pedaling forces (downward direction). Assuming a proper functioning setup, there should be very little suspension movement when pedaling, even when standing in a sprint. That is the whole point of the system.
That said, the Brain usually has a blue knob that controls sensitivity of the Brain opening. Verify the setting that you have it in. I would test by setting it into the most closed/restrictive position, and then test the movement static on the floor, and when pedaling on a smooth road. It should remain very stable with minimal bob.
If it moves a bunch, that implies the valving is messed up and in need of maintenance.
Thank you. That is what I suspected but didn’t want to hear.