How to: Bleeding The Brakes

[weekendrider]

I've put my Mity-Vac back in the box and now use only the syringe.
Not only does it pull fluid but you can push fluid too.
Is it quicker to try and work an air bubble down against it's nature or push it up where it wants to naturally go? Last time I farted in the tub the bubbles came up to the top not down the drain. Wet rags on things you don't want to damage is always good in case of a spill.

 

[michaelpthompson]

OK, trying to bleed the front brake on my '75 XS650B. PO said it worked fine when he parked it (of course), but the reservoir was dry. I put a wrench on the bleeding nipple (looks like a grease zerk, is that right?), got a tube onto the nipple, other end in the standard peanut butter jar. Filled the reservoir and began pumping, just trying to get fluid down the line. A tiny bit came out of the nipple, but after that, no matter how much I pumped, nothing was flowing. Tried pumping with the valve closed, no discernible change in pressure. Opened it again, pumped some more, no change in reservoir fluid level.

Am I doing something wrong, or is perhaps the seal gone bad in the MC?

Pics of my setup in case I'm not doing this correctly.

 

[zeroxs650]

I worked on the front brake and added fluid to the tube at the nipple, had lots of air bubbles then it stopped. I continued for about 20 minutes pumping the lever 5 times then holding the lever as tiny amount of bubbles came up to the reservoir. Still no change in the pressure at the lever nor does the fluid travel through the tube though you can see the movement of the fluid. Any other suggestions or do I need to be more patient and eventually it should work?

 

[figure8]

As was suggested to me by a member here, leave the lid off the master cylinder overnight and use some twine or a zip tie on the lever to keep it engaged. This gives a chance for all the air bubbles to escape.

 

[zeroxs650]

Will give it a try....

 

[Brassneck]

I worked on the front brake and added fluid to the tube at the nipple, had lots of air bubbles then it stopped. I continued for about 20 minutes pumping the lever 5 times then holding the lever as tiny amount of bubbles came up to the reservoir. Still no change in the pressure at the lever nor does the fluid travel through the tube though you can see the movement of the fluid. Any other suggestions or do I need to be more patient and eventually it should work?

More patience... it's one of those things that takes a while, then all of a sudden...bam, it works.

I like the 3-5 small little pumps on the lever, then one big pump and hold, open bleeder valve...wait a second or two, close valve...and repeat.

 

[5twins]

MichealP, if no fluid is flowing you probably need to disassemble the system and clean it out. These old brakes need that more often than not. You will probably be amazed at all the crap you find inside and wonder how the brake could even function. Well, many times they don't, lol.

 

[zeroxs650]

Tried to bleed the front brake and got a syringe. What a mess, got fluid everywhere when I tried to push the fluid through the valve. I did leave the top off of the master cylinder and zip tied the lever to the grip. Got lots of air out but still not change in pressure. Will the mytvac be a better option or just need more patience?

 

[weekendrider]

When you push the piston in (lever tied to grip) you have covered up the relief hole?
So you are pushing against a seal (the piston). In effect trying to pressure the line, which it sounds like you did. There should be little to no resistance using the syringe.
With the syringe and hose on the bleeder. Open the bleeder valve. Do not apply the piston or pull the lever. Pull/suck some fluid into the line. It will flow past the piston seal. The fluid level in the m/c reservoir should be lower. Now push the fluid back through and look for air coming out of the relief port in the master cylinder.
Repeat till you don't have any bubbles coming from the caliper when you pull the plunger nor any from the relief port. At this point you will be moving fluid back and forth between the syringe and m/c reservoir. Fill your reservoir to the desired level, tighten the bleeder valve and cap the m/c.

 

[zeroxs650]

Thanks weekender, will give it a go….

 

[TwinLewi]

Awesome thread. Can’t really screw anything up with step by step like this!
I want to rebuild my caliper. Looking for a how to for that now.

 

[gggGary]

not exactly a rebuild thread but the biggest issue with the two piston calipers is getting BOTH pistons out. read here http://www.xs650.com/threads/stuck-pistons.43080/

 

[TwinLewi]

not exactly a rebuild thread but the biggest issue with the two piston calipers is getting BOTH pistons out. read here http://www.xs650.com/threads/stuck-pistons.43080/

Great link. Only thing I will have a hard time with is getting the pistons out. I don’t own a air compressor.

 

[gggGary]

Caliper is small, you must know somebody with an air compressor? Take c-clamps and rags. you can pump one piston out quite a ways with the master cylinder before you pull the brake apart.

 

[TwinLewi]

Caliper is small, you must know somebody with an air compressor? Take c-clamps and rags. you can pump one piston out quite a ways with the master cylinder before you pull the brake apart.

I knew ton of people in the states with a compressor. Trouble is I just moved countries 7 months ago to Australia.

 

[ReycleBill]

I had a stuck one just yesterday. I knocked the crap of of the caliper with a big rubber dead blow hammer. Rang like a bell. And freed it right up.

 

[TwinLewi]

I will plan to use a bit of all these tricks. Hopefully one or two works. It is kind of nice that I am getting new lines seals (the works) I can just drain the fluid. Replace the lines and work on the caliper. Is there much fluid left over in the caliper after I remove the fluid from the lines? I am thinking there will be a little spray of excess fluid when I use the air to help work the pistons out.

 

[gggGary]

You can drain "most of the brake fluid" out by manipulating but a brake fluid mess is about unavoidable on an overhaul. Will say again wrap the caliper in a rag or use a c-clamp as a stop, compressed air can and will send a piston violently across the room. Talk around a bit you'll find someone with an air compressor and may find some new friends in the bargain!

 

[TwinLewi]

Well it just so happens that today my buddy Coops purchased a compressor!!!! Awh winning! Time to send some Pistons flying!! Well just kidding. C clamp for sure! Btw I see a lot of rust on these pistons.

 

[gggGary]

Inside of pistons is always rusty, unfortunately outside is also usually rusty.