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How to bleed rear brakes?

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I replaced my rear master cylinder, and I had a vacuum pump hooked up to it, and it was sucking fluid through. The pedal still goes straight down without any bite, and I can't understand why. How else can I try bleeding it?

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Oh man the last time I did this it was such a mother f&$king pain. I ended up removing the caliper and positioning it so it was higher then the master. I also rotated it to get any air pockets out. It took way too long. But eventually the feel comes back once the air is out. 

 

 

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Yeah can be a pain to get all the air out... I once had to reverse bleed my brake line by using a syringe full of brake fluid connected to the bleed nipple on the caliper and slowly push fluid back into the reservoir. Might be worth a shot?

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Okay cool, I'll have to try it out. I've been using front brakes only but u don't want to buy just front pads lol

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Just remember to keep the fluid flow slow and steady and in time with opening of the bleed nipple... And don't forget about the fluid level in the reservoir. I've also used this method to flush really old fluid that turned into gel... Anyway..good luck.

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I recently had the worst experience doing this on my YZ250. I would first try to reverse bleed as someone suggested (especially if line is dry). After a couple of pumps, the brakes should stiffen right away.

If that doesn't work, the vacuum bleeders are cheap (around $40) and those work well too but the reverse bleed is quicker and usually can do the job.

If you've pumped more than a bottle through, I would stop and reassess. I pumped a couple of bottles through only to realize one of my seals on my newly rebuilt MC was nicked! I was able to build some pressure, but not full pressure to be enough for actually braking. Those seals need to be in perfect condition otherwise they'll let fluid leak internally and won't create proper pressure. Also, you should obviously double check that they're installed in the correct direction.


Hope this helps.

Good luck!

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image_18294.jpg

I find that the reverse bleed is the best way on rear brakes. Bouncing the pedal a bit while pumping helps get the air out faster. I use a squirt bottle like this one to push the fluid through. I have a bottle used exclusively for brake fluid, since many of the machines that I work on professionally have difficult to bleed brake systems. One other thing that is helpful is not to push the caliper piston in further than is absolutely necessary when changing the pads. 

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Just did this after my full rebuild with new brake lines. Make sure everything is clean as can be, blow everything out with an airline etc.

Reverse bleed to begin with until the master is full, close nipple. Attach hose and run into bottle on the floor, few pumps of pedal, then keeping it compressed crack the nipple. Repeat until you get a brake.

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All the push bleeding and vacuum bleeding in the world won't reposition an air bubble in a caliper nook.  I take the whole system off and to the bench with the caliper highest and a vacuum pump on it. I get it in all kinds of angles tapping with a screwdriver handle to dislodge the air bubble.  As mentioned, piston all the way in helps.

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Letting it sit overnight after bleeding may allow the air to rise to the highest point.  We had a problem recently bleeding the rear brake on my son's CRF450R after replacing the hose.  Bled it for awhile, then came back the next day and bled it a bit more and it was fine.

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1 hour ago, cjjeepercreeper said:

Letting it sit overnight after bleeding may allow the air to rise to the highest point.  

Put some pressure on the circuit by using a zip tie to compress the brake pedal (works with hand brake too). leave the system pressurized overnight. That usually forces all the air into the MC.

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Make sure your using proper brake fluid, there is a difference however in my experience, open bleeder and keep reservoir full once fluid starts draining from bleeder close bleeder and pump brakes alot and hold down brake and crack bleeder to let air out, close bleeder and start over many times

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When I bled my rear breaks I couldn't get no pressure build up I ended up just opening the nipple and pressing down the break lever and before releasing the lever I'd put my thumb over the nipple hole then push break lever down again and pull thumb off let fluid come out and repeat!  it eventually got its pressure back

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