Changing / Bleeding the Brake Fluid - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
 
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post #1 of 1 (permalink) Old 01-15-2006, 11:20 AM Thread Starter
 
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Changing / Bleeding the Brake Fluid

I don't have a power bleeder and don't want to get brake fluid on my tank but I've got a real need to change my used-motor oil color brake fluid out for some cleaner stuff.

Changing the Brake Fluid:

I would suggest the following.

You will need some clear tubing to fit snuggly over the bleed valve. Clear and clean glass jar.

Put the tubing on the bleed valve and the other end into the glass jar. Remove the master cylinder cover. Make sure you have a fresh new bottle of brake fluid. Brake fluid sucks up moisture real quick. If you use old stuff, I mean stuff that been sitting on your shelf for awhile, it may have water in it unless it was factory sealed.
Now comes the fun part. You may want to have someone help with this. Firmly squeeze the brake lever. Do not release it. Now open the bleed valve. Brake fluid will flow into the jar and you will feel the brake lever relaxing and getting closer to the grip. Still do not release the lever. Tighten the bleed valve. Now release the lever. If you release the lever before tightening the bleed valve you will just suck the old stuff right back into the calipers.
Squeeze the lever again and repeat with the bleed valve. Keep doing this and keep an eye on the level of brake fluid in the master cylinder. Refill as needed before it starts sucking air. Eventually you will flush out all the old stuff. This may take awhile. If you watch the fluid as it goes through the tube, you will see when the fresh stuff starts coming out. Continue for a few more cycles after that.

For pros only - One variation is to keep pumping until the master cylinder is sucking air, then refill with fresh brake fluid and then do the lever, bleed valve steps I gave above. Refill as needed because now you do NOT want the master cylinder to suck air. Some people may say this is bad, bad, bad but there is some logic behind it. If you let the master cylinder suck air then refill, you will get air into the system. But you are bleeding the system so when you get to the point where you see air in the tubing, you know most of the old stuff is gone. A few more cycles after that, the air will be gone and the old brake fluid will be gone. Keep the cycles up until no more air is seen in the tubing. If you have never changed brake fluid before I suggest NOT doing it this way.

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Hey Joe. The way I did mine was cover my tank and lower part of my bike with plastic. Run a small hose from the bleeder to a container. Take master cylinder cover off and start pumping your break lever. You have to be sure to keep putting new fluid into the master cylinder as it goes down so as not to get air in the line. Once you have clear fluid coming out the other end you are good to go. Just do one side at a time. Its kinda slow but will get the job done.
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I do just as everyone else talked about, only I use a turkey baster first to remove the fluid in the master cylinder. Why waist time pushing the bad fluid through first.
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I just wanted to add here that before you cover your bike with plastic..to move the master cylnder on the handlebars in such a way that it is level. ususaly done by moving the front wheel to the left and loosening the bolt and rotating it on the bar if need be....then tighening it back down.I take a paper towel and cut a hole in it to go around the master cylnder to protect the paint on the bar clamps. Make sure you are using the correct type of brake fluid...Dot-4 I believe. When your done...bolt the cover on and wipe off the cylnder with soapy water..Then repositioon the lever back if need be. You can get the plastic tubes for the nipples at a store that sells aquariums fairly cheap.
This is something I learned a long time ago for bleeding the air out. Works like a charm as I've done it about a half-dozen times in the past 15 years or so... Did it on my VN750 when I first got it and haven't had to retouch the system until now when I need to change out the fluid... Bleeding hydraulic brakes via constant pressure: (works on cars, bikes, etc.) Check the brake fluid level in the reservoir. Make sure it is at the proper level. Pump the brake a few times until you get plenty of pressure. If you can't get constant pressure, there may be a leak somewhere in the system. Push or pull the brake lever as tight as you can. Somehow secure it there. If in a car, use a broomstick on the seat, etc. If on a bike, use some type of non-stretching rope or twine. Make sure to cover anything that might be damaged like the seat material or the throttle material. If on a bike... Wrap the twine or rope or twine a few times and pull the brake lever tighter if you can. Wrap some more. The tighter the better. After wrapping around tie it off so it can't slip loose. Let it sit for around 12-14 hours - overnight if possible so you don't have any temptation to tinker with it. I'm not sure if the air escapes or dissolves into the fluid at high pressure over time, but it doesn't come back on cars and hasn't come back on the bike I did either. YMMV of course. If your brake line lets go during the holdover period, it was a sign that you probably needed one anyway. Better to blow while standing still than on the exit ramp. However, I have never heard of this happening.
Don't forget.. we also have a write-up in Files > Maintenance Tips > Bleeding Brakes (Yahoo Board)

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I do as Gary does on my bikes and cars - suck out the old contaminated stuff. Then I do what I think is the easiest bleed method - gravity bleed! Fill the master with fresh fluid after you've removed the old stuff, loosen the bleed valve on the caliper and watch the old fluid run out. Don't let the master cylinder run dry. This is a great method if your working alone. You can bleed both brakes in 20 mins. Tech Tip:If your brake lever is spongy for whatever reason (other than a leak) use a tie wrap to hold down the brake lever overnight or an entire day. The air bubbles will rise into the small air cavity above the DOT4 fluid in the master cylinder and you'll be amazed at how firm that lever is.
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I bleed the brakes on my bikes every spring and my cars every 1-2 yrs. Hydraulic clutches every 2 yrs. The key is to change it before it breaks down and looks dark brown. Most new bike manuals recommend every 1-2 yrs so you know it's important because they usually list fluid changes at much greater intervals than most of us follow.
Bleeding hydraulic brakes via constant pressure: (works on cars, bikes, etc.) Check the brake fluid level in the reservoir. Make sure it is at the proper level. Pump the brake a few times until you get plenty of pressure. If you can't get constant pressure, there may be a leak somewhere in the system. Push or pull the brake lever as tight as you can. Somehow secure it there. If in a car, use a broomstick on the seat, etc. If on a bike, use some type of non-stretching rope or twine. Make sure to cover anything that might be damaged like the seat material or the throttle material. If on a bike... Wrap the twine or rope or twine a few times and pull the brake lever tighter if you can. Wrap some more. The tighter the better. After wrapping around tie it off so it can't slip loose. Let it sit for around 12-14 hours - overnight if possible so you don't have any temptation to tinker with it. I'm not sure if the air escapes or dissolves into the fluid at high pressure over time, but it doesn't come back on cars and hasn't come back on the bike I did either. YMMV of course. If your brake line lets go during the holdover period, it was a sign that you probably needed one anyway. Better to blow while standing still than on the exit ramp. However, I have never heard of this happening.

Oh cool...I can explain this.. Air bubbles in fluids at low pressures can "adhere" to surfaces. Pour a glass of carbonated soda in a glass and sometimes you can see tiny bubbles clinging to the sides of the glass, part way up from the bottom. Tiny air bubbles in your brake lines can do the same thing. When you apply pressure strongly to the lever, you increase the pressure in the lines. Liquids can not be compressed, but gasses can. Air bubbles under higher than atmospheric pressure do not "stick" as well as those at low pressures.So they have a better chance of rising to the top of the liquid. In the twists and turns of the brake lines they may simply collect together at some spot.If they do , their larger size will also coax them to rise. This is one of the reasons premium brake lines have teflon coatings inside. The fun comes when, although you can't see it, you release the pressure. The tiny bubbles still stuck expand suddenly...and again being larger, will tend to rise now. The super small ones in the fluid are suddenly not that super small now, and follow suit. (This is why divers have to slowly accend..the rapid change in pressure makes the super tiny bubbles of air in their blood expand) It's a good idea when doing this proceedure on your bike, and even when bleeding you lines normaly to take a hard object (like a 10 inch 3/8" drive extension is what I use) and tap the lines fairly hard along their length, starting at the bottom near the calipher. This coaxs the small bubbles to release themselves from the brake line walls and rise like they ought to. KM
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