Front brake caliper ques.

[dr.danh]

My front brakes are wore and will be replacing them. Ques. Once the brake calipers are applied what relieves the pads off the disc. Just the lack of the hydr. pressure?  If caliper pistons are sticking then the pads wouldn't go back into place. And cause excessive pad wear. Correct? Any easy way to pull the pistons and sand then with seals?

[matt]

Yup when you release brake tgere is a square cut seal that will bring piston back just a little so brakes release.  If you use search  you will find answers for rebuilding. Things needed compressor,  block of wood, new seals and brake fluid

[RonW]

Ques. Once the brake calipers are applied what relieves the pads off the disc. Just the lack of the hydr. pressure?  

Affirmative, after the hydraulic pressure is released, the spinning rotor nudges the pads a mm away from the rotor's surface. Not like drum brakes which have a return spring to retract the brake shoe away from the drum.

If caliper pistons are sticking then the pads wouldn't go back into place. And cause excessive pad wear. Correct?

• Any easy way to pull the pistons and sand then with seals?

I'd stay away from pulling them pistons fully out from their bores .... just to clean them up. A better option is to place a paint stick etc. between the old pads and apply the brakes. This should push the pistons just enough out of their bores to expose any hidden grit that needs cleaning. You can clean the ring around the collar on the pistons with a strip of cloth or strip of fine sandpaper wrapped around the pistons.

[hubcapsc]

Ques. Once the brake calipers are applied what relieves the pads off the disc. Just the lack of the hydr. pressure?  

Affirmative, after the hydraulic pressure is released, the spinning rotor nudges the pads a mm away from the rotor's surface. Not like drum brakes which have a return spring to retract the brake shoe away from the drum.

If caliper pistons are sticking then the pads wouldn't go back into place. And cause excessive pad wear. Correct?

• Any easy way to pull the pistons and sand then with seals?

I'd stay away from pulling them pistons fully out from their bores .... just to clean them up. A better option is to place a paint stick etc. between the old pads and apply the brakes. This should push the pistons just enough out of their bores to expose any hidden grit that needs cleaning. You can clean the ring around the collar on the pistons with a strip of cloth or strip of fine sandpaper wrapped around the pistons.

I've taken my calipers apart any number of times. The brakes are real nice with
the calipers/pistons all cleaned up, pins greased, new pads... I've thought about
Ronw's short cut several times, and I bet it would pretty much get you the
same thing... as long as you can push the pistons out far enough to get
to the entire "ring around the collar"...

I think this picture would be "not far enough"...



-Mike

[Hook#3287]

I would do as Ronw suggested now and rebuild them completely this winter.

Nothing like freshly rebuilt calipers, makes you realize how bad they were.

[RonW]

hubcapsc, if memory serves I got the paint stick idea from an earlier post of yours. I think was yours was accompanied with a pic. Also, I'm thinking about using an internal plumbing wrench to rotate the pistons. If I ever find where I put it, but I do have it somewhere. I ain't buying another one.

*Pulling the piston is definitely the better way to go, but I have nightmares big time about getting all the bubbles out of the brake line. Probably take longer than putting back the bolts on the rear fender siderails, until you know the trick of course accordingly.

[Cliff]

hubcapsc, if memory serves I got the paint stick idea from an earlier post of yours. I think was yours was accompanied with a pic. Also, I'm thinking about using an internal plumbing wrench to rotate the pistons. If I ever find where I put it, but I do have it somewhere. I ain't buying another one.

*Pulling the piston is definitely the better way to go, but I have nightmares big time about getting all the bubbles out of the brake line. Probably take longer than putting back the bolts on the rear fender siderails, until you know the trick of course accordingly.

What is the diameter of internal plumbing wrench needed?

[WintrSol]

I wouldn't use any grit of sandpaper - not only does it remove the polish from the surface, those fine scratches are a good place to start a leak. A strip of denim soaked in brake fluid or brake system cleaner works well enough for me.

[Dorkman]

Another method:  Soak a shoelace in brake cleaner, then buff around the piston like you're doin' your shoes.  I would also stay away from fine sandpaper . . . you may take off a bit too much.

[RonW]

Excellent idea!

The strips of cloth that I've been using worked better if the fabric material does not have a tendency to stretch a lot. As the material stretches the width becomes too narrow and the flat strips start to become round like a cord, same with the flat shoelaces if they're the elastic type, I would think. And, okay then, sandpaper isn't the best material. Many years of repeated sanding is bound to undersize the OD of the piston and so on & replacement Oem pistons are $20 each yikes. Any thoughts on using braided de-soldering wicks.

What is the diameter of internal plumbing wrench needed?

I don't know. I was merely thinking out loud but thanks the same for listening.

[BigBod]

Go ahead and pull the pistons out completely. Replace both seals in the calliper. Most importantly, clean the recess where the seals sit. 9 times out of 10 it is the corrosion in the recess that forces the seals out of place and make the piston stick.

Best thing I have found to clean the recess is a dremmel with the small wire brush wheel attached, works a treat.

As for the pistons, polish them up on a polishing wheel. Don't know if you can get them over there, but here we can buy aftermarket pistons in stainless steel.

[RonW]

How difficult is it to get all the bubbles outta the brake lines? (after complete disassembly)

[Jess from VA]

I get the pistons almost but not completely out.  I then use a pistol cleaning rod with brass/stainless brushes and bore solvents (Hoppes, Shooter's Choice).  You can access every nook and cranny, and my brakes are spotless when done.   Blow crud out with brake cleaner spray.

[gordonv]

Wow, I would hate to see how/what you do to clean your guns!   

[RonW]

hmmmm, I always thought of a bike as being a loaded gun.

[BigBod]

How difficult is it to get all the bubbles outta the brake lines? (after complete disassembly)

It really isn't that bad, much easier with 2 people. If you get to a point where it's almost done but still a bit soft...if it's the front brake, tie the lever hard against the bars and turn the bars so the fluid reservoir is at it's highest point, chances are all the bubble will rise up over night...when you untie the next day will probably be perfect..

You can do the same with the rear to a certain extent, jam a bit of wood on the brake pedal and under the bars...

[BigBod]

I get the pistons almost but not completely out.  I then use a pistol cleaning rod with brass/stainless brushes and bore solvents (Hoppes, Shooter's Choice).  You can access every nook and cranny, and my brakes are spotless when done.   Blow crud out with brake cleaner spray.

Waste of time if you've got crud behind the seals. The only way to do it properly is to remove the pistons completely.

[Paladin528]

If you pull the pistons out you should get a brake bore hone and hone the bores out.  This will make sure the bore is clean and allow the seals to do their job.
The piston itself has no sealing or contact properties to the bore, it is the rubber that is doing all the work.
I would say break em down, clean the crap out of them, Hone the bores, new seals, grease the pins, put new pads on and reinstall em.
Then the fun of bleeding them.  Pressure bleeder or speed bleeders are your friend here.

[Jess from VA]

Waste of time if you've got crud behind the seals.

I guess I don't because my brakes are perfect and responsive.... and squeaky clean.