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Old July 16th, 2014, 09:44 AM   #1
N-m
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Rear Brake Lever Travel is Excessive and Rear Brake won't Lock Tire.

Background:

I completely pulled and cleaned the rear braking system on my '06 with less than 5,000 miles. Caliper was disassembled and cleaned and works well. Disc is above minimum thickness. Line was replaced with Galfer SS. Rubber hose from reservoir to MC was replaced with OE part, and reservoir was thoroughly cleaned. I did not tear into the rear MC but it seems to work well. The disc and pads are factory and the pads still have life. I have new pads but decided against using them just yet.

I have bled, rebled, hung a weight overnight and searched for another air bubble. I get nothing at the bleeder but fluid.

Performance:

You could stop with the rear if you were alone in the desert with miles of pavement. This morning while standing on gravel I hung my whole leg off the lever and could still drag the bike w/o the rear tire locking up. Not only that but the lever has inches of travel.

If I replace pads I will eliminate some lever travel due to thicker pads but it's not going to correct two inches or more and will return as pads decrease in thickness.

What do I want? A lever that is not all mushy, has only a small amount of travel and can lock the rear down if I lay into it. Are my standards too high?

What is next step? Bleed, replace existing pads, adjust lever?
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Old July 16th, 2014, 09:56 AM   #2
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Possibly you still have some amount of air in the system/caliper that your tore apart. Or... your rear rotor is pretty glazed over. A light sanding should take care of a glazing problem.

I don't think your standards are too high, sadly... it should all too easy to lock the rear.
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Old July 16th, 2014, 10:57 AM   #3
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Sounds like too much pad/piston travel. Try taking the caliper off the disc and push the pistons out a little using the brake lever, (make sure not to go too far and push them out of the caliper) then spread the pads enough to go over the disc. Should be an improvement.
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Old July 16th, 2014, 12:16 PM   #4
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my guess is worn rear master cylinder.
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Old July 16th, 2014, 12:32 PM   #5
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Quote:
Originally Posted by csmith12 View Post
Possibly you still have some amount of air in the system/caliper that your tore apart. Or... your rear rotor is pretty glazed over. A light sanding should take care of a glazing problem.

I don't think your standards are too high, sadly... it should all too easy to lock the rear.

Link to original page on YouTube.

Bleeding the back brakes is pretty easy since the pedal and caliper are so close. Try bleeding with the thumb method where before you open the bleed nut place your thumb over the hole then open the bleed valve. Put a little pressure on the pedal before you let your thumb off then bleed as normal using your thumb instead of a wrench to open and close the valve. I wrap the caliper with a shop towel to soak up the fluid and wear gloves.

Make sure the seal in the master cylinder didn't get bunched up when you replaced the lid. You sure the new line is on nice and tight with crush washers on there?

I use my back brakes quite a bit but I was considering switching to non-sintered pads because I've had experience locking up the back brake in bad situations like after it rains and its not fun.

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Old July 16th, 2014, 12:59 PM   #6
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Or use a handheld vacuum pump to suck all the air out.. be mindful of the reservoir level when doing this, it drains quickly.
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Old July 16th, 2014, 01:11 PM   #7
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Quote:
Originally Posted by csmith12 View Post
Possibly you still have some amount of air in the system/caliper that your tore apart. Or... your rear rotor is pretty glazed over. A light sanding should take care of a glazing problem.

I don't think your standards are too high, sadly... it should all too easy to lock the rear.
Pulled caliper, held at highest point and bled again after vigorous shaking of bike tail end while pumping lever in similar manner. (I hope my Momma doesn't read that.)

While caliper was off I took some Emory cloth to both sides of the disc. I tried this on the old pads but decided the small amount of pitting that covered a large amount of the face of each pad could be causing me issues so I chucked those and installed the new ones.
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Old July 16th, 2014, 01:14 PM   #8
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Quote:
Originally Posted by baxtc1 View Post
Sounds like too much pad/piston travel. Try taking the caliper of the disc and push the pistons out a little using the brake lever, (make sure not to go too far and push them out of the caliper) then spread the pads enough to go over the disc. Should be an improvement.
I did this several times, gently without wood wedges between the pads and hard with the wedges in place.

I did notice that each piston seemed to slide easily, but if you remove pads and then gently pressurize caliper one piston begins moving long before the other. Sticky pistons that need to be replaced?
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Old July 16th, 2014, 01:15 PM   #9
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Quote:
Originally Posted by crazymadbastard View Post
my guess is worn rear master cylinder.
I was hoping you wouldn't say that. I will check into rebuild kit and rice of rebuil/new MC just in case.
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Old July 16th, 2014, 01:17 PM   #10
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Quote:
Originally Posted by agentbad View Post

Link to original page on YouTube.

Bleeding the back brakes is pretty easy since the pedal and caliper are so close. Try bleeding with the thumb method where before you open the bleed nut place your thumb over the hole then open the bleed valve. Put a little pressure on the pedal before you let your thumb off then bleed as normal using your thumb instead of a wrench to open and close the valve. I wrap the caliper with a shop towel to soak up the fluid and wear gloves.

Make sure the seal in the master cylinder didn't get bunched up when you replaced the lid. You sure the new line is on nice and tight with crush washers on there?

I've been doing this. I am 99% certain the hydraulic portion of the system is in great shape from an air standpoint. I can't find any air no matter where I look or what I do.
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Old July 16th, 2014, 01:18 PM   #11
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I did all of the above and threw in the new pads. Lever travel decreased dramatically and the lever feels more solid now. I am about to run another errand and will report back. Thanks for all the info and help.
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Old July 16th, 2014, 02:46 PM   #12
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I had a similar thing when I changed the rear tire recently.
I had pushed the pads apart to make it easier to slot the disk back in and the brake would not work afterwards. Pumped it dozens of times but that sucker would not grip.and the travel stayed long.
Left it to make a cup of tea and when I tried again everything snugged up in a couple of presses like usual.

One thought I had was that, with the long strokes of closing up the caliper, possibly the master cylinder piston had got stuck in internal deposit of the years near the top of its travel where it doesn't usually wander.
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Old July 16th, 2014, 02:51 PM   #13
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Quote:
Originally Posted by Ninjinsky View Post
Left it to make a cup of tea and when I tried again everything snugged up in a couple of presses like usual.
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Old July 17th, 2014, 04:10 AM   #14
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The Man! Tea, toast, and a Ninja with unlocked rear brakes. How you gonna beat that?
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Old July 17th, 2014, 04:13 AM   #15
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Quote:
Originally Posted by Ninjinsky View Post
I had a similar thing when I changed the rear tire recently.
I had pushed the pads apart to make it easier to slot the disk back in and the brake would not work afterwards. Pumped it dozens of times but that sucker would not grip.and the travel stayed long.
Left it to make a cup of tea and when I tried again everything snugged up in a couple of presses like usual.

One thought I had was that, with the long strokes of closing up the caliper, possibly the master cylinder piston had got stuck in internal deposit of the years near the top of its travel where it doesn't usually wander.
I see exactly what you mean about the long travel distance of the cups resulting in a long travel distance of the lever. You have to pump the lever several times to account for that. Let me make clear that AFTER I did this I was experiencing about 2 inches of travel with the old pads.

Currently the rear is working really well with the lever feel and distance being much more responsive and shorter. Still not where I would like for it to be but a ton better than yesterday.

I will be riding this morning and hope to try out the "drag the rear tire with brakes locked across gravel" technique to see if I can lock up the rear in that situation now. If not I am sure I will be closer.

Thanks to everyone for their input. We are getting there.
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