My New Ride!
Road Warrior
Joined: Dec 2007
Posts: 1,605
Likes: 2
From: Mesa AZ
I Had The same problem with my front brakes and foolowed the instructions from a guy on another forum named Moc Mike. Solved my problem and was easy to do! give it a whirl! Herb
(Your problem is very likely not your fluid, it's your caliper piston seals stuck to the pistons:
First, you have to understand the system.
These fixed caliper, dual piston brake systems have no internal springs, or mechanical pad retraction devices like automobiles, to free up the pistons after the brakes are released. They very primitively rely on the "memory effect" of the oddly shaped piston seals to very slightly draw the piston back off the rotor, so she don't overheat.
When you apply the brakes, the piston is forced outward, and in turn, distorts the trapezoidal cross section o-ring that seals it to the bore. When you release the brakes, that seal wants to roll back to it's original position, resting the piston and relaxing the pad friction somewhat (there should always be light contact with the rotor, even at rest).
As the brake pads wear, the resultant and ever increasing gap between the pad and rotor must be accomodated for. There is no mechanical "adjustment" to the caliper or pad, but adjustment is done automatically by that seal allowing the piston to slide further outward from its grip, as the pads wear. (remember those orange "Push ups" you used to get from the ice cream counter?)
Now that you understand the mechanism, let's look at what can screw that up....
If the surface of the piston has any kind of grime, grunge, or corrosion, or just becomes dry under the seal contact area, it will stick itself to the seal, and not be allowed to slip and self adjust, so when you apply the brakes, the seal distorts more than it was meant to, and when you release the brakes, the seal retracts the piston too far from the rotor, requiring more lever movement to operate the brakes. Two identical bikes can have very differing lever movements because one or more pistons in the system is stuck to its bore seal.
OK! HOW DO WE FIX IT!:
Fixing the problem can be as simple as grabbing a handful of brake lever hard and fast, or as complicated as a caliper disassembly and cleaning, but more often than not, the fix is found somewhere in the middle...
If slamming the brakes won't adjust the system properly, get out a few wrenches, and turn on the tunes, and recruit a helper. You need to :
1.) unbolt one caliper from the forks, remove the pads,
2.) clean the outer circumference of the two pistons (still in their bores!) by spraying liberally with brake cleaner spray.
3.) Now force both pistons as far back into their bores as they can go.
4.) Put the brake pads BACK IN THE CALIPERS, then work the brake lever until the pads touch each other in the center of the space. If one pad moves inward, and the other doesn't try to hold some pressure on the moving one so the other one is forced to move. Spray and clean the exposed circumference of the pistons again.
5.) Work the pistons back into their bores by gently and slowly separating the pads with a brake tool or dull screwdriver, and repeat this as many times as it takes to get the pads to touch in the center of the caliper space, then do the same thing with the other caliper after reinstalling the first one.
WARNING! You MUST use pads between the pistons, otherwise you'll pop them out of the bores and be forced to bleed the system.! Using the technique described above will not require any bleeding of the brakes.
Working the pistons in and out of their bores like that will help clean and lubricate the surface of the piston and unstick it from the grip of the bore seal. Then, when you finish installing the last caliper, check and fill the reservoir back up if it needs it, cap it off, then grab a hard handful of lever to reset the pistons and pads to the rotor.
This SHOULD set your system up for minimum slop at the lever. )
(Your problem is very likely not your fluid, it's your caliper piston seals stuck to the pistons:
First, you have to understand the system.
These fixed caliper, dual piston brake systems have no internal springs, or mechanical pad retraction devices like automobiles, to free up the pistons after the brakes are released. They very primitively rely on the "memory effect" of the oddly shaped piston seals to very slightly draw the piston back off the rotor, so she don't overheat.
When you apply the brakes, the piston is forced outward, and in turn, distorts the trapezoidal cross section o-ring that seals it to the bore. When you release the brakes, that seal wants to roll back to it's original position, resting the piston and relaxing the pad friction somewhat (there should always be light contact with the rotor, even at rest).
As the brake pads wear, the resultant and ever increasing gap between the pad and rotor must be accomodated for. There is no mechanical "adjustment" to the caliper or pad, but adjustment is done automatically by that seal allowing the piston to slide further outward from its grip, as the pads wear. (remember those orange "Push ups" you used to get from the ice cream counter?)
Now that you understand the mechanism, let's look at what can screw that up....
If the surface of the piston has any kind of grime, grunge, or corrosion, or just becomes dry under the seal contact area, it will stick itself to the seal, and not be allowed to slip and self adjust, so when you apply the brakes, the seal distorts more than it was meant to, and when you release the brakes, the seal retracts the piston too far from the rotor, requiring more lever movement to operate the brakes. Two identical bikes can have very differing lever movements because one or more pistons in the system is stuck to its bore seal.
OK! HOW DO WE FIX IT!:
Fixing the problem can be as simple as grabbing a handful of brake lever hard and fast, or as complicated as a caliper disassembly and cleaning, but more often than not, the fix is found somewhere in the middle...
If slamming the brakes won't adjust the system properly, get out a few wrenches, and turn on the tunes, and recruit a helper. You need to :
1.) unbolt one caliper from the forks, remove the pads,
2.) clean the outer circumference of the two pistons (still in their bores!) by spraying liberally with brake cleaner spray.
3.) Now force both pistons as far back into their bores as they can go.
4.) Put the brake pads BACK IN THE CALIPERS, then work the brake lever until the pads touch each other in the center of the space. If one pad moves inward, and the other doesn't try to hold some pressure on the moving one so the other one is forced to move. Spray and clean the exposed circumference of the pistons again.
5.) Work the pistons back into their bores by gently and slowly separating the pads with a brake tool or dull screwdriver, and repeat this as many times as it takes to get the pads to touch in the center of the caliper space, then do the same thing with the other caliper after reinstalling the first one.
WARNING! You MUST use pads between the pistons, otherwise you'll pop them out of the bores and be forced to bleed the system.! Using the technique described above will not require any bleeding of the brakes.
Working the pistons in and out of their bores like that will help clean and lubricate the surface of the piston and unstick it from the grip of the bore seal. Then, when you finish installing the last caliper, check and fill the reservoir back up if it needs it, cap it off, then grab a hard handful of lever to reset the pistons and pads to the rotor.
This SHOULD set your system up for minimum slop at the lever. )
Hail to the KING!!! You will enjoy your new scoot.
Thread Starter
|
Tourer
Joined: Aug 2009
Posts: 383
Likes: 1
From: Boston & thereabouts
Thanks All!
Yeah, I can tell - this bike's gonna be a good thing. A real good thing!
Cheers, and thanks all!
JR
Last edited by JR-Boston; Sep 24, 2009 at 08:21 PM.
Road Master
Joined: Aug 2005
Posts: 830
Likes: 0
From:
I have an 05 RKC, and I can help you spend your money. 
First thing I would do is change ALL fluids. This is a recommendation for anyone buying a used bike.
You can do a search on the so-called best fluids, but HD Syn3 in all three spots is a good start.
I would change the plugs.
You sound as if you need a clutch adjustment too.
If you're a fairly new rider, and unable to do all the maintenance, I would suggest you pay the few hundred dollars to a dealer, and get the bike a full 5K service.
That would take care of the fluid changes, clutch adjustment, and some other items that warrant a good look in a used bike.
I would also highly recommend they look into the brake issue.
Back to spending money:
I have the Monsters Ovals, and I love them. I also have true duals, power commander, K&N air filter, and just about every catalog item available for my bike.
I've also added tunes, lowers, and a low profile windshield.
Here are a couple pics to wet your appetite:
First thing I would do is change ALL fluids. This is a recommendation for anyone buying a used bike.
You can do a search on the so-called best fluids, but HD Syn3 in all three spots is a good start.
I would change the plugs.
You sound as if you need a clutch adjustment too.
If you're a fairly new rider, and unable to do all the maintenance, I would suggest you pay the few hundred dollars to a dealer, and get the bike a full 5K service.
That would take care of the fluid changes, clutch adjustment, and some other items that warrant a good look in a used bike.
I would also highly recommend they look into the brake issue.
Back to spending money:
I have the Monsters Ovals, and I love them. I also have true duals, power commander, K&N air filter, and just about every catalog item available for my bike.
I've also added tunes, lowers, and a low profile windshield.
Here are a couple pics to wet your appetite:
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