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Tman

Front brakes draggind- no pad retraction

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The cause of pad retraction is not subject entirely on the return spring in the master cylinder. There is ALSO a significant reaction based on the characteristics of the main piston bore seal holding to the piston. This is why the retraction is only a slight degree compared to the extension of the piston stroke. The rubber seal gets deformed in its place to be pushed forward and forced outward from its recess groove. This coupled with the release of pressure in the fluid ( by the master cylinder return spring) allows the force now held in the deformed seal to pull the piston rearward enhanced by its secure fitment on the outer diameter of the piston. That is why the seal is square.

 

 Now the second realization is HOW the sliding caliper works. Since there is no hydraulic piston on the far side of the caliper, only a wall holding another brake pad....there is no hydraulic force generated behind this pad to bring it into intimacy with the rotor disk. This is important to realize. Without the sliding action of those pins allowing the caliper body to slide freely AWAY from its initial positioning on the rotor disk ( by not being a solid unit)  to a more backward position, closer to the fixed  part of the caliper mount...the outer pad will not be brought..INWARD...into contact with the rotor. This is done by a backward force pushing the caliper itself away from the disk while stil maintaining the first pad’s contact with the rotor.Its a first single inner pad contacting the disk...than pushing the caliper rearward to bring the outer(hub side) pad against inner side of the rotor.  Now both brake pads are clamped against the disk.

 

 The only other way to make both sets of brake pads clamp onto the rotor... without the movement of a sliding caliper.... is by pro viding a hydraulic chamber and pistons on the far side of the caliper to give a moving brake pad its impetus  pushing the pads inward while the calip[er body is fixed to its mounting on the fork leg. you will note that the  pad spring actually is notched so that this pad will not slide by design. It is fixed against the back wall of the caliper.

 

 This now provides you with crucial information to realize how necessary it is to properly use the flexibility and the clamping axle bolts to center the wheel’s axle and rotor disks   to maximize the outboard pad's clearance on caliper installation. There is a limited amount of pad retraction on the piston side of the caliper.   Make the axle location adjustment for a definite  clearance with the fixed brake pad.... when the brake hydraulic  force is inactive. That way the retraction force of the pads is maximized( as little as it is.)

 

Cleanliness and polish on those slide rods  is critical as well as a good silicon grease.,  Inside the boot that covers their exposed end. And their freedom to move independently of the caliper body HAS to be obvious when its mounted on the fork. If the caliper is not properly positioned  relative to the  the disk,  the pad retraction on the side without pistons  will be slight to none at all and this all depends on the amount of return slide action it is permitted when the Hydraulic pressure is off.   The only variable you can control is the location of the disk relative to the caliper and the free action of the caliper slide rods  in the rubber grommets.

This information is critical to understand why there is a drag on the brakes. And the reason for  little  free spin of the front wheel when brakes are released.

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Great explanation Tman , very clear and concise. Thanks.

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I always find that pictures help me to understand. 

 

This image is a screen-shot captured from the digital version of the 1998-2001 Honda VFR800FI Interceptor Service Manual, Chapter 13, Page 15.

 

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I'm guessing that this checking of clearance (and, obviously, re-adjusting the front wheel axle placement if necessary) to get 0.7mm on both sides has the effect of optimizing the spacing for the brake return-slide action.

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I need a clear photo of the hydraulic line connections on the left front caliper. There is a very short hyd line termination that is under quite a bit of stress. The factory manual is sorely lacking in this detail ALso not much help from Clymer manual.  I couldnt find a picture anywhere on internet.

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