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I commented on an old post in the trike section but thought it might be better here.
If thats not ok by the moderators please move/remove at your discression.
A lot of people do not realise how the caliper seal works.

It is a square section seal but the groove it sits in is not square bottomed, the bottom is at an angle to the piston bore so that when the seal is fitted it turns into a diamond cross section.

This means only a corner of the seal is against the piston, if there is a big gap to the pad fluid will push the piston the seal starts to twist and then the piston pushes through the seal, untill the pad touches the disc.

Once the piston has to only move a fraction the seal twists as the brake is applied and it is only this twist in the seal that pulls the piston away from the pad so not a lot of retraction force.

Consequently the seal groove needs to be spotless and from years of experience i can assure you that water in brake fluid corrodes the groove and leaves behind some concrete like crap. So much so thay i have found you need to use a dental pick to dig it out as a dremel wire brush just polishes the crap and leaves it shiny but still there.

Hope this helps you understand how it all works and what to do to rebuild a caliper so it works for years.

Cheers

Bryan
 

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I knew that
I commented on an old post in the trike section but thought it might be better here.
If thats not ok by the moderators please move/remove at your discression.
A lot of people do not realise how the caliper seal works.

It is a square section seal but the groove it sits in is not square bottomed, the bottom is at an angle to the piston bore so that when the seal is fitted it turns into a diamond cross section.

This means only a corner of the seal is against the piston, if there is a big gap to the pad fluid will push the piston the seal starts to twist and then the piston pushes through the seal, untill the pad touches the disc.

Once the piston has to only move a fraction the seal twists as the brake is applied and it is only this twist in the seal that pulls the piston away from the pad so not a lot of retraction force.

Consequently the seal groove needs to be spotless and from years of experience i can assure you that water in brake fluid corrodes the groove and leaves behind some concrete like crap. So much so thay i have found you need to use a dental pick to dig it out as a dremel wire brush just polishes the crap and leaves it shiny but still there.

Hope this helps you understand how it all works and what to do to rebuild a caliper so it works for years.

Cheers

Bryan
. I knew that. Learned it from Mark Martin. He would only use the quadring (square cross section) in his race cars. He knew that a true O-ring (round cross section) did not pull the piston back as far if at all. That made the brakes drag a little more. That meant the car would roll harder. That could slow the car by .01 seconds per lap and cost a race. :).
 
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