Topic: Brake Piston Won't Retract, Tried Everything

[Popwood]

My front disc brake still drags slightly after caliper rebuild on '75 550K. Installed new piston and seal after thorough cleaning of cylinder. Flushed system and started with fresh brake fluid. Carefully adjusted stationary brake pad. Removed brake arm and cleaned and lubed pin. Used a high E guitar string to make sure return fluid hole in reservoir not clogged. Bled system, of course. Master cylinder was rebuilt just a few years ago when braided stainless lines were also installed. All paint from the brake pad had been removed on earlier work and this time I slightly beveled the edges of the pad. Pad seems a good fit.

Just how far should the guitar string be inserted in the reservoir hole. I'd say I got it in about a half inch. I can see fluid being returned, flowing into the reservoir after release of brake.

I'm pretty certain the problem lies with the piston not fully returning. I just did the same work on my CB750 that had a worse drag problem and it now works perfectly.

In the FAQ on brakes I read someone reams the return fluid hole slightly enlarging it. Is that a good idea? And if so, should the fluid fluid be drained first? And how do you ever chuck such a tiny wire into a drill?

Any and all ideas welcome.

[pjlogue]

Several things to check, if your brake lines are old, the inside lining can become delaminated from the wall and act like a check valve preventing pressure release in the caliper.  You cleared the pinhole in the MC.  Have you taken the MC apart and cleaned everything?  If your MC plunger does not retract freely to expose the pinhole the pressure can't be released from the caliper. 

There is nothing special or complicated about these brakes.  It is important that everything be in good condition (MC, calipers and lines) and everything to be clean inside for it to work properly.

One last thing to check is the pucks.  They need to be lose and not bind in the MC.  Some dirt or paint on after market pucks can cause problems with the brake dragging.

-P. 

[MauiK3]

Help us with "drags slightly"
These brakes will rub a bit on one side or another when at rest, you can hear it when you push the bike around. This is normal, they won't float freely and have clearance on both pucks all the time, if ever, they just won't be squeezing the disc.

[Popwood]

Drags slightly defined. With front wheel off the ground I can spin the tire and it will make perhaps one to two revolutions.

[rotortiller]

Sometimes the o-ring groove in the caliper gets corroded reducing space and binds the puck. Remove the o-ring and make sure the groove is clean, if you have not already done so.

[strynboen]

thek the tiny return hole in the marster beholder..all presure need to bleed back through that hole..if it are blocked..pressure holds up ,in the caliber

[PeWe]

Agree about old sloppy brake lines.
I have not had that problem, but a friend had that on an old car, brake did not retract on one wheel.
 Brake hose had deliminated and worked as a valve, one direction only.

[bryanj]

If you cleaned the caliper seal groove with a dremel brush it dont work properly, you need to clean out all the hard crap with a dental pick or similar first

[Popwood]

I'm certain the groove in the cylinder is clean, including the inside corners. I inspected it closely using a dentists mirror so I could view the "blind" corner.

That tiny fluid return hole. . . . I can get a guitar wire in about 1/2". Should I be able to insert deeper? Thoughts on my description of how the wheel "drags" now. It rubs the moveable pad operated by the piston. Can get one to two wheel revolutions after spinning the wheel. Some say here that's to be expected, rarely ever runs truly free. Is what I'm experiencing about as good as it gets?

[pjlogue]

I'm certain the groove in the cylinder is clean, including the inside corners. I inspected it closely using a dentists mirror so I could view the "blind" corner.

That tiny fluid return hole. . . . I can get a guitar wire in about 1/2". Should I be able to insert deeper? Thoughts on my description of how the wheel "drags" now. It rubs the moveable pad operated by the piston. Can get one to two wheel revolutions after spinning the wheel. Some say here that's to be expected, rarely ever runs truly free. Is what I'm experiencing about as good as it gets?

One way to test if it is the pad rubbing is to compress the piston into the caliper so the pads aren't touching the rotor and then spin the wheel again.  If it has the same drag then it's the bearing grease and bearing seals causing the friction.  (possibly the bearing too)  If the wheel spins freely then you know it's the brakes causing the drag. 

-P.

[Popwood]

I have compressed the piston into the cylinder and the wheel does turn freely, no rub at all. New wheel bearings were installed less than 1,500 miles ago.

[Popwood]

I should add that this topic subject line may be a bit misleading. Should say "Won't Fully Retract".

When break leaver is applied, the wheel will stop spinning immediately and has a tight grip on rotor. Just doesn't retract enough to stop the pad from rubbing the rotor.

[bryanj]

You dont say if you have the adjuster bolt and spring fitted?

[Don R]

 Ride it for a while and break in the brakes. It's not dragging enough to burn anything up. On a car we try to do 20 easy stops before any hard use, I do that on new brake parts also.

[Popwood]

Yes, the stationary pad is properly adjusted. I also removed the break arm and cleaned it up, including the pin and hinge, lubed pin and hinge then reinstalled, then adjusted the adjuster screw. Stationary pad has about 6 to 8 thou clearance between it and rotor.

[vik351]

I have compressed the piston into the cylinder and the wheel does turn freely, no rub at all. New wheel bearings were installed less than 1,500 miles ago.
[/
quote]

End of problem IMHO they rub a bit after application for a hard stop, stop... and when ya drive off they rub for two seconds and then all good, it makes it's own bees dick gap which is all it needs...

When ya sit there slowly pushing the wheel and can hear it going Slish Slish Slish, at speed it just aint the same...

Same a trying to ride a 2 MPH compared to 20 MPH ,

vik...

[ADW]

Yes, the stationary pad is properly adjusted. I also removed the break arm and cleaned it up, including the pin and hinge, lubed pin and hinge then reinstalled, then adjusted the adjuster screw. Stationary pad has about 6 to 8 thou clearance between it and rotor.

After reading all your posts and the replies, it sure sounds to me like your brake is operating normally. As people have said, there IS a light rubbing that essentially always will be there, as it's a characteristic of a disc brake system. Sounds like yours is fine...ride the bike and enjoy!

[web]

If it does drag too much, there is one very easy way to eliminate any hydraulic causes : just loosen the bleed screw.

If a delaminated hose or the MC hole or whatever else in the circuit is blocking and keeping the pressure on, it will free up immediately when you crack open the bleeder.

Still drags too much? Then it's the piston or its seal.

[low-side]

In my experience, this is more normal than having no drag at all.  Like Hondaman said, pad kiss is a characteristic of disc brake systems.  With our calipers on swinging arms, our bikes usually have a little more of it than most others.

[maxheadflow]

One issue with these brakes, single piston / caliper floating on a pin, is that the pads may not be seating well on the disk with new pads or slight misalignment.  As long as the wheel isn't dragging severely, take it for a ride and see if it gets better.  If not pull the caliper apart and check the pads to see where they are wearing.  You may find them wearing with more pressure in one spot other than center. If you can't see, you can crosshatch the face of the pad with magic marker and run. File the high spots.

[jaytee-nz]

A long shot but it has happened before - is your fender mounted between the fork leg and the caliper arm ? If so, this is incorrect and could cause the pads to not align properly to the brake rotor (they need to be to parallel to the rotor) which could cause the pads to not retract fully. The fender must be mounted to the inside of the caliper arm.

[Popwood]

The fender is mounted properly; fork leg, brake arm, fender mount. But for a minute I thought you were on to something until I read your post a couple times.

Temperature warmed up to 50 today so I took it our for about ten miles of in town/stop-go riding. I had two stops along the way for parking. At each stop I felt the rotor to get a handle on any heat/friction problem. The rotor was barely registering any warmth; nothing more than I'd associate with normal riding/breaking. When I got home and in the garage I propped the front end to give the wheel a spin and it wouldn't make a full rotation, but I need to break a few times getting up the driveway and into the garage. Nonetheless, I am going to go with those who counsel this slight rub is normal unless someone chimes in otherwise. I'll keep an eye on it although there won't be much riding over the next few winter months.

Thanks to everyone for weighing in and offering their thoughts and suggestions. I really appreciate all the help.

[Spanner 1]

You may have swapped the stationary pad with the piston pad when you put it back together.  Piston pad will not stick in the caliper , stationary 'prolly .

[web]

If the rotor is cool, so are you. No issue.

[mattsz]

If the rotor is cool, so are you. No issue.

Words to live by!