Rear Brake Pads

[Ralph Werner]

After removing the rear brake assembly to bleed the system with the valve pointing up, the brake pads now don't seem to move. What happened?

I had to pry the pads apart slightly to fit them back onto the rotor and now there is no rear brake. I'm sure that I did something pretty stupid but I can't figure out what.

[Guest ratchethack]

Ralph, if you give a brief description of your procedure, I'll give it my best shot.

[jrt]

The rear brake is prone to dust/dirt buildup. Perhaps a good cleaning, or actually pulling the pads out, then cleaning might help.

[Ralph Werner]

Here's what happened. I removed the caliper assembly so that the bleeder was pointing up. After the new fluid was added and bled, the pads were touching each other. I separated them enough to get the assembly back onto the rotor but then I had no brakes at all.

It's possible that when I separated the pads that it forced fluid out of the reservoir because the cap was not on.

 

I have the assembly off again but now when I add fluid and bleed, sometimes I get air bubbles and sometimes no fluid movement at all. The pads still don't come together but I can feel them doing some movement (with my finger) when I press on the brake pedal. I have never removed brake pads before (plenty of brake shoes though). Is it possible that I sprung them out of position? I did hear a clicking sound and there seems to be spindles that they rest on.

 

Sure would value any input here.

[Mike Stewart]

Ralph,

 

It is normal when you spread the pads apart that the master cylinder reservoir fills with fluid. This is how some bike mechanics bleed the air from the brakes.

 

When I first read your post, I had the feeling that the caliper seals could of been damaged from the pistons coming out too far (pads touching). This still could be the case, but should not cause the pads to get stuck. Also, you would have a leak at the caliper when you apply the rear brake.

 

Have you tried pumping the rear brake pedal many times to move the pads back to the rotor? You could remove the caliper again and watch the pistons/pads to see if they come out some with every stroke of the rear brake pedal. If they don't, I would rebleed the rear brake.

 

Alot of times, I just gravity bleed the brake systems. Have the bleeder up like you have done and crack the bleeder. Just let the gravity of the fluid leak out and just add to the master cylinder as needed. No pumping needed

 

If you are in need of a master cylinder or rear brake caliper, PM me.

 

Good luck,

Mike

[Ralph Werner]

It looks like I have a bunch of air in the system (I guess from pushing the pads apart and forcing fluid back throught the reservoir. I don't see any piston movement and when I try the standard bleeding, I get air but very little fluid.

[Guest ratchethack]

It looks like I have a bunch of air in the system (I guess from pushing the pads apart and forcing fluid back throught the reservoir. I don't see any piston movement and when I try the standard bleeding, I get air but very little fluid.

53425[/snapback]

Ralph, from your description it sounds to me like you may not have experience bleeding brakes. That's OK, you came to the right place. It also sounds like you got more air in your system than you lost in the process, which leads me to believe that you may not have worked the bleeder nipple properly when bleeding.

 

The bleeder nipple should be thought of as a valve. You need to operate the valve in the right sequence while bleeding to make sure that you're pumping the fluid in only one direction only - NOT in both directions. If you've previously just repeatedly pumped the brake pedal with the bleeder nipple left open, you very likely sucked air back into the caliper through the nipple with each release of the brake lever, filling the caliper with air. This would result in the symptoms you posted.

 

The bleeding procedure is:

 

1. Fit a clear tube on the bleeder nipple to catch the old fluid in a container and open the nipple.

2. Push down on the brake pedal slowly, AND HOLD IT DOWN with no upward movement. Fluid will pump out into your container.

3. Close the bleeder nipple.

4. Let the brake pedal back up.

5. Repeat the above sequence until the fluid runs absolutely free from bubbles in the tube. You have to watch the level in the reservoir while you're doing this to MAKE SURE you don't let it get too low, or you'll just be pumping air in from the top!

 

You said you took the caliper out and pointed the bleeder nipple up. This is good, it's the only way you have any chance of getting all the air out. As I posted here awhile back, if you tilt the caliper slightly from side to side and rap on it with a mallet or block of wood while bleeding, I found that this helps a great deal in releasing trapped air and getting it moving it up and out while bleeding. It will help to have someone assist with this part.

 

I also noted in the same post that a block of wood should be wedged between the pads or (if you took the pads out, the caliper pistons) to prevent them from coming out while you're bleeding the system. Again, YOU DON'T WANT THE PISTONS TO COME OUT!! As Mike noted, you can damage the piston seals from excessive piston travel even if the pistons have not come all the way out.

 

I like taking the caliper off to bleed for another reason, beyond using gravity to expel air bubbles. It's easy enough to do, and you can prevent the tendency of the pistons from hanging up in these bikes due to buildup of baked-on brake dust, which I think is made worse by an under-swingarm caliper. With the caliper in hand, if you take out the pads and brush out the calipers thoroughly with a toothbrush and flushing with solvent in a container, you'll likely find a horrendous amount of crap coming out of there unless it's been done recently. Paying special attention to the circular grooves around the pistons gets it all out.

 

As noted at length in my last post on this, brake fluid is powerfully hygroscopic. If you've had your bottle of fluid sitting open for any length of time, I highly recommend that you do youself a favor. Have a brand-new bottle on hand for your next effort. The stuff is cheap, and after all - good brakes are more important to your health than good power. Keep it capped as much as possible (as well as the reservoir on your bike!), and stash that old bottle with your discarded old fluid and all your other stuff for the recycler.

 

Good luck!

[Ralph Werner]

Thanks for the posts. I'm getting there. Actually, I have bled brakes before but I never sucked that much air (probably because I tried to do it without removing the caliper). I had used a speedbleeder but it seemed like the one way valve wasn't working so I went back to the standard fitting.

[Guest Nogbad]

I did mine today together with a pad change.

 

I never bother taking the caliper off to invert it. First, push back the old pads and wedge them fully retracted with wooden wedges against the disc, 2 halves of an old clothes peg do the job great.

 

With the pads fully retracted, there is virtually no free volume within the caliper, so the air will easily be pushed out by the fluid even with the nipple pointing down.

 

Fit some clear tubing to the nipple, and make it long enough to reach the bottom of a jam jar resting on the ground.

 

Put a small amount of fresh fluid in the jar, sufficient to cover the end of the tube. The air will bubble through the fluid and will not be able to re-enter the tube when the pedal is released.

 

Open the nipple half a turn, and pump the pedal smartly, topping up the reservoir until the fluid emerging from the tube is fresh and clean.

 

On the last stroke, wedge the pedal down against the stop and tighten the nipple no more than 1/8 turn from hand tight.

 

Remove the tube, wipe up and top up and close the reservoir.

 

Remove old and fit the new pads with a thin smear of anti seize on the backs, and on the short sides.

 

Pump the pedal to put the pads in contact with the disc.

 

Job done.

[Ralph Werner]

Well I found the problem sort of. When the bleeder valve is closed, fluid still comes out of the end when the brake is pumped. I have three valves and they all do the same thing. I didn't overtighten any of them and the seat in the caliper body looks fine. Any ideas?

[gh67]

Well I found the problem sort of. When the bleeder valve is closed, fluid still comes out of the end when the brake is pumped. I have three valves and they all do the same thing. I didn't overtighten any of them and the seat in the caliper body looks fine. Any ideas?

53439[/snapback]

Under the clutch bleeder valve there is a little ball bearing that the bleeder seats against...if this is gone, the bleeder valve will just continue to flow fluid. I've not had my brake apart yet, is there a similar ball bearing in it as well?

[Ralph Werner]

Problem solved. It looks like the bleeder valve had bedded into the caliper body. When I loosened it to bleed the system, it wouldn't seat tightly again. Fluid came out of the valve opening when I pressed the brake pedal (thus the air and very little pad movement). I put the bleeder valve in a drill, used a fine file, fine sandpaper, and polishing cloth. It seated right in and presto - no leaks. Never would have suspected this.

 

Thanks again for all of your fast and thoughtful input!

[Guest ratchethack]

Ralph, please accept my apologies for having misread your capabilities!

 

Congrat's on solving the problem!

[Ralph Werner]

No apology needed - my capabilities as a mechanic would not earn me a living. You and Mike had some great input!

[Ralph Werner]

A post on WILDGUZZI cleared up the mystery. Apparently some Speedbleeders were machined at the wrong angle and leaked! :!:

 

In my case, I guess that the initial installation distorted the opening in the Brembo body and then would not re-seat properly a year later.

 

I'm getting so full of knowledge in my old age that my brain may pop! Stand clear!