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How to bleed your front brakes (change out fluid) (Read 530 times)
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How to bleed your front brakes (change out fluid)
02/16/13 at 06:40:00
We have a long history of teaching newbies how to bleed their brakes, but nobody ever made it into a Tech Posting before now. So, here it is in chronological order (giving first, second and third credit where it is due).
I've been working on bikes since before they had disc brakes. I usually drain & refill mine at least once a year so I've had lots of practice.
I get a length of 3/16" clear tubing long enough to reach from the bleeder screw to the master cylinder. I fill the m/c, put the hose on the bleeder screw & open it about 1/2 turn & hold the free end of the tubing in the fluid in the m/c reservoir. Keeping the free end down in the fluid, I slowly pump the brake lever until I have a solid stream of fluid in the hose. I then close the bleeder screw & remove the hose from the bleeder. If you clamp the hose just above the bleeder before you take it off, you won't even make a mess. This has always worked for me & gives the firmest lever of all the methods I've used for years. It works because when you release the lever, it will draw fluid into the hose & not air, & when you squeeze the lever the air will bubble out. Just keep the free end IN THE FLUID so you don't draw air in.
Between my 2 bikes & my friends, I do this several times a year. It even works for rear disc brakes too, as I found out when I did my V-Star 950 the first time.
I first came up with this idea in 1980 when I put a disc brake front end from a '72 Norton Commando on my '70. After spendng a frustrating day going through the m/c & caliper, cleaning & rebuilding both, I still couldn't get it to work. I tried this & was done in 15 minutes. You don't forget what works when you've been as frustrated as I was that day.
You need to loosen the bleeder screw on caliper itself... If you've never done it before, find someone to help you... These are your BRAKES and you need them to work correctly.
The process is... Attach a hose (I used aquarium hose from the local pet shop) to the nipple of the bleeder on the caliper. Loosen the bleeder screw, with the reservoir filled (I always put the cap/lid back on, didn't screw it, but laid on top - I also propped the bike up so that master cylinder was level), pump the brake lever 4 to 5 times, hold the lever in and tighten the bleeder screw... Let out on the brake lever. Loosen the screw, pump 4 to 5 times, tighten the screw, let out on the brake lever. Repeat this until you have a full stream of brake fluid coming out of the tube with NO BUBBLES... Remember to keep the reservoir filled, as you'll be draining it when bleeding. I had to add fluid 4 or 5 times during my bleeding.
Things to keep in mind... Do not close the bleeder screw with the brake lever OUT... And do not open it with the brake lever pulled in.
Again... If you don't know what you're doing... Get someone that does to help you. These are things that you don't want to fail when you need them
Oldfeller's variant on the same old trick, used when changing out brake fluid
(which you should do every year or so, BTW)
Changing the fluid out on your front brakes for a brand new person totally unused to bike mechanical work takes on the order of a half hour of time, with 1 helper mebbe required during the last little bit when you are manipulating the bleed valve while under pressure.
Paladin, do you stick a piece of clear tubing on the end of your bleeder valve nipple so you can clearly see your air bubbles stopping and starting and so you can clearly see when you fluid becomes all nice and clean and new? This is important when you are changing out your brake fluid when it gets all nasty on you.
Some get all fancy going back up to the handle bars with the tubing, but I find that several feet of the same tubing going down to the floor then over and rising up over the edge of a catch bowl does the exact same job, and if you are changing out all the brake fluid you are going to need that catch bowl for all the yuky brake fluid.
I find that a like 3 feet of clear tubing, once it becomes full of fluid, it also acts as a check valve for the return stroke. I pump down by myself (spending my attention up top keeping the reservoir nice and full) and when I see a clear fluid stream in the tube (and no air bubbles) I finger tighen the valve until it will just barely pass fluid and give it a resistance squeeze or two at the lever and on the last one I clinch the bleeder valve off in mid stroke with my foot to make durn sure no air can get in on the return stroke.
(cause there ain't no return stroke, it got pinched off while I was still pushing)
So, using some clear tubing to act as your "check valve" can allow you to do it by yourself with complete assurance you have no air in your system.
NOW HERE IS THE SUBTLE TRICK THAT MARKS THE EXPERT.
You AWAYS make durn sure the threads and the little inside areas on the brake slave cylinder nipple are plumb full of brake fluid
by loosening the nipple a goodly bit at the very first, stoppering it off with your finger and then pressure pumping at it with the brake lever until you note that a flow of brake fluid is coming out the threads. The threads and empty voids are now plumb full of air free brake fluid. So now you finger tighten it back up to the point it just barely is passing fluid and start back to pumping.
Now put the clear hose on and follow everybody's best method to pump your master cylinder and brake lines full of clean bubble free brake fluid,
knowing that no air can make it back through all the fluid in the clear tubing and the fluid that is trapped inside that long continuous spiral of fluid filled thread intersection on the nipple threads
You don't need no expensive speed bleeders or other extra money gizmos, just a piece of clear tubing and a little trick or two.
If you are changing out a brake line you need to fill the new line up with fluid or the system won't pump at all -- use the baggie trick to fill the new brake line up.
(poke the brake line in through the corner of a baggie, put a rubber band over the intersection to keep it from leaking, put brake fluid in the baggie then seal the baggie and squeeze it gently to force brake fluid down through the brake line. It also helps to slightly loosen the fitting on the bottom so the air can get out while you are baggie squeezing, but I figured you figure that out on your own)
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Re: How to bleed your front brakes (change out flu
Reply #1 -
02/16/13 at 20:22:48
Thanks for the write-up, Old.
Here is another trick:
If my aim is to change brake fluid, I start out by suctioning (using your tool of choice)
(not all) of the old fluid from the brake fluid reservoir. Don't remove so much old fluid that you expose any of the holes at the bottom of said reservoir.
Then, refill said reservoir with fresh, clean fluid. You are now ready to begin the brake fluid changing process.
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