Several of you have asked about piston seal grease. We are talking about the seal which holds the caliper piston in place.
A quick recap on the piston seal. Yes it keeps brake fluid from leaking out and allows the piston to move smoothly in and out. But a critical function of the seal is to pull the piston back when the brake pedal is released. If the seal is not operating as it should then the piston will continue to exert some residual force on the disc – brake drag.
The seal deforms when the caliper moves against the pads and this deformatino stores a certain amount of energy. In fact the seal is cut at an angle in order to maximise the energy stored by this deformation. When the brake pressure is released this stored energy is released as the seal returns to it’s original shape and pulls the piston back as it does
As the surface of the seal is pushed tightly against the piston body any lubricant will over time be squeezed out. How long the lubricant remains depends on the physical characteristics of the lubricant – some lubricants will last longer than others…Nevertheless applying a lubricant like ProSlip PIN which is very low friction and will not react with the seal material improves the seal function. This will improve ‘pedal feel’ – braking feels less harsh – as the piston retracts quickly off the pads elimination brake drag.
Red rubber grease is not a suitable piston seal lubricant – it’s not a low friction lubricant and is too thick to remain long between seal and piston