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lexintexan

Rear brake help / bleeding not working

6 posts in this topic

So today I greased my linkage and swingarm bearings. While I was doing the job, I accidentally pressed the rear brake lever when there was no rotor in the caliper. I didn't think anything of it and finished the linkage maintenance. When it came time to put the back wheel back on and button everything up, I noticed i couldnt get the rotor into the caliper! the whole assembly had shifted to the right, and the slot between the brake pads no longer lined up with the rotor. I managed to get the caliper to re - align with the rotor with a screwdriver.

My question is this; Did I mess something up or blow a seal by sticking a screwdriver between the pads and spreading them to force the caliper's piston back into the caliper? Or possibly by letting the piston go out too far? Now my back brake doesn't work and seemingly no amount of bleeding is helping. I am getting quite a few bubbles in the bleed hose. should I try to do a complete flush of the system? Is it possible I damaged the brake line when I was taking the swingarm off? There are no visible leaks. Could a hole be small enough to let air in and not let fluid out? :thumbsup:

PS it is a 2006 yz450f

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I think it's very unlikely that you damaged anything by pushing the piston back how you described it. Make sure the pads are property installed. Also make sure to pump the brake pedal many times after the caliper and pads are installed. It takes quite a few pumps to get the piston out far enough again to press the pads against the rotor. If you still can't build any brake pressure by pumping about 10 times, try bleeding the rear brake and make sure you use proper bleeding technique (there should be tons of threads on bleeding your brakes on this forum, just do a search). Good luck!

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Disc brakes have no return springs; once the pads move in toward the rotor, they stay moved. It's a common trick to make wheel installation simpler by pushing the pads back, and this will ALWAYS result in the brakes "going to the floor" without working at first. As was pointed out, just pump the pedal at a moderate rate until the solid feel comes back.

There are two possible problems that can result from pushing the pedal or lever with the rotor out of the caliper. The first is where the pads move out so far the pistons move clear of their seals, dump fluid, and gulp air. For the most part, this is impossible on most dirt bikes unless both pads are removed, and you would have seen the fluid.

The second problem, one that can happen, is that the level in the master cylinder may have been low enough to allow air in at the top of the system when the level dropped as a result of moving the pads into the space where the rotor should have been.

Normally, you should have been able to have pushed the pads back, reinstalled the wheel, and pumped down the brake until it worked again. But if you gulped air from the master cylinder, or let it in from the bleeder screw, you'll have to bleed it. My favorite way to fill and bleed the rear brake from scratch is to remove the caliper and let it hang so the hose fitting is at the high point, instead of the bleeder. Then, loosen the fitting at the master cylinder end of the hose, connect a tube to the bleeder screw, and a funnel, or a squeeze bottle or syringe full of brake fluid to that. Open the screw and fill it from the bottom up until only fluid comes out the hose at the M/C. Close the bleeder and mount the caliper.

Then fill the master and push the pedal through only the first 1/4" or so of its travel several times to bump the air bubble at the fill port out of the way. Watch the level in the reservoir, as it should begin to drop as fluid runs through to the hose fitting. When fluid comes out fairly free of air, snug the fitting up. Open the bleeder and push the outer pad back slightly. Only fluid should come out. Close the bleeder. Loosen the M/C fitting and push the pad a bit more. again only fluid should come out, but if there's residual air, you get it, too. While the fitting is loose, push the pedal down and HOLD IT THERE to see if any air comes from the master. Close the fitting before releasing the pedal, check the fluid level, and repeat if there was air present.

You may still have to pump the pads back out against the rotor, and if that's the case, you will want to watch the fluid level as you do.

Air will not obediently move through the brake system and out the bleeder. It will keep moving back toward the high spot, which in this case is the master cylinder fitting, and can actually sit there and not move as fluid flows around and under it. It can be quite frustrating, but once you visualize how it behaves, you can deal with it.

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Thanks for the responses guys! This was a frustrating event as I have never had a brake issue like this before. I purchased a mity-vac for 45 dollars at my local motorcycle shop and was quite un-impressed. In fact it didn't work at all for me. The way I finally was able to fix the brake was by "reverse bleeding" the system as Grayracer had described. I wound up not removing the caliper from the swingarm and using a syringe and a piece of tubing. I loosened the master cylinder fitting and let brake fluid pour out of the fitting as I pumped the new fluid in with the syringe. closed up the valve and the fitting and viola great brakes again! What a waste of 45 bucks!

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Disc brakes have no return springs; once the pads move in toward the rotor, they stay moved. It's a common trick to make wheel installation simpler by pushing the pads back, and this will ALWAYS result in the brakes "going to the floor" without working at first. As was pointed out, just pump the pedal at a moderate rate until the solid feel comes back.

There are two possible problems that can result from pushing the pedal or lever with the rotor out of the caliper. The first is where the pads move out so far the pistons move clear of their seals, dump fluid, and gulp air. For the most part, this is impossible on most dirt bikes unless both pads are removed, and you would have seen the fluid.

The second problem, one that can happen, is that the level in the master cylinder may have been low enough to allow air in at the top of the system when the level dropped as a result of moving the pads into the space where the rotor should have been.

Normally, you should have been able to have pushed the pads back, reinstalled the wheel, and pumped down the brake until it worked again. But if you gulped air from the master cylinder, or let it in from the bleeder screw, you'll have to bleed it. My favorite way to fill and bleed the rear brake from scratch is to remove the caliper and let it hang so the hose fitting is at the high point, instead of the bleeder. Then, loosen the fitting at the master cylinder end of the hose, connect a tube to the bleeder screw, and a funnel, or a squeeze bottle or syringe full of brake fluid to that. Open the screw and fill it from the bottom up until only fluid comes out the hose at the M/C. Close the bleeder and mount the caliper.

Then fill the master and push the pedal through only the first 1/4" or so of its travel several times to bump the air bubble at the fill port out of the way. Watch the level in the reservoir, as it should begin to drop as fluid runs through to the hose fitting. When fluid comes out fairly free of air, snug the fitting up. Open the bleeder and push the outer pad back slightly. Only fluid should come out. Close the bleeder. Loosen the M/C fitting and push the pad a bit more. again only fluid should come out, but if there's residual air, you get it, too. While the fitting is loose, push the pedal down and HOLD IT THERE to see if any air comes from the master. Close the fitting before releasing the pedal, check the fluid level, and repeat if there was air present.

You may still have to pump the pads back out against the rotor, and if that's the case, you will want to watch the fluid level as you do.

Air will not obediently move through the brake system and out the bleeder. It will keep moving back toward the high spot, which in this case is the master cylinder fitting, and can actually sit there and not move as fluid flows around and under it. It can be quite frustrating, but once you visualize how it behaves, you can deal with it.

gray

what type of hose did u use? I tried a carb hose and accomplished bloody knuckles (bleeder valve). i need to change my front brake hose.

my plan was this

1remove the top hose connect to the m/c

2install the new hose at the top without losing fluid in the m/c (need helper)

3remove the bottom fitting (old)

4install new hose at the bottom fitting

5connect a hose to the bleeder and pump in new fluid from the bottom until i no longer see bubbles

6 pump the brake, tap the line, and bleed from the bottom also try to spread the calipers

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