Brake bleeding

[shoggoth80]

Hey guys,
I know brake bleeding is supposed to be a simple process...
I have replaced the front brakes on my '78 GS550, and I can't get the front level to firm up. No matter how many times I pump it, it doesn't feel like it is building any pressure. The master cylinder should be fine, as it was fine before I did the pad swap. I know I got air in the lines, as that would more or less go without saying. Is it just a LOT of air in the lines that is causing it to feel this way? I haven't actually started the bleeding process, as I wanted to ask about this symptom first; see if it might be something a little more annoying.

 

[grips11]

Sounds to me like there is air in the line. Bleeding the line is the best way to get rid of the air bubbles, no way around doing it. The process is a slow one. Trust me I've done it. And there is no way of knowing how far the air bubbles has traveled up the line. So, grab a big jar and a clear tube and start the bleeding process. When there are no more bubbles, the breaks will respond nice and firm. Atleast thats what we're hoping...\\/

 

[shoggoth80]

That's gotta be a lot of air. Oh well... at least it doesn't sound like anything more annoying than that.
Time to get messy.

 

[Steve]

One place that collects bubbles (and is often overlooked ) is the banjo bolt at the master cylinder. Just crack it open a bit, squeeze the lever, tighten the bolt, release the lever. Repeat a few times, but be sure to have a rag positioned to catch the fluid before it hits any paint or plastic.

At the wheel end, use a piece of clear tubing slipped over the bleed nipple and put the other end in a small jar (baby food jar works well) that has enough brake fluid in it to cover the end of the tubing. Loosen the bleeder, squeeze the lever (hold it in), tighten the bleeder, release the lever. Repeat until no more bubbles come out of the tubing.

Always start with the furthest bleeder, then work closer to the master cylinder. Also, check the fluid level in the master cylinder often to make sure it does not run dry.


.

 

[Guest]

Take off the brake light switch, brake lever and the master cylinder lid. Push in the master cylinder piston with a phillip head screwdriver as far in as you can. You should get a nice blast of bubbles that the lever couldn't get cause it doesn't press in the piston all the way.

 

[tomcat24551]

One place that collects bubbles (and is often overlooked ) is the banjo bolt at the master cylinder. Just crack it open a bit, squeeze the lever, tighten the bolt, release the lever. Repeat a few times, but be sure to have a rag positioned to catch the fluid before it hits any paint or plastic.

Steve's procedure worked for me!

I replaced my brake lines a couple of years ago, but could not get all the air out of the system. Bled and bled and bled at the calipers and got nothing but clean fluid. Still, too much play in the lever at the master cylinder. So I positioned the master cylinder and the handlebars so that the master cylinder banjo bolt was the highest point in the system and just let it set for a week or so. Every day I tapped all the lines, hoping to dislodge any bubbles so that they would rise. Then I used the above procedure and guess what--problem solved. Remember, the master cylinder is the highest point in the system, so all the bubbles are eventually going to try to rise to that point.

One other point: Dot 3 and 4 brake fluid is water soluble, so if your rag fails to catch it all, wash the affected area with clean water immediately and you shouldn't have any problems. Best advice? Catch it all!

Tomcat

 

[tomo]

A handy tip I picked up is to bleed the brakes as normal, then after nipping the bleed nipples back up, pump the lever several times until you feel a bit of pressure, even if the lever feels spongy, then on the last pump hold the lever in, then use a cable tie around the lever and handle bar to hold it in. Leave the cap on the master cylinder resevoir loose, put bike on side stand and turn bars so the resevoir is on the higher side, then leave bike for about 24 hours. Cut the tie, fit the resevoir cap back on, and you should find you have a good brake now. It`s worked for me really well in the past. I guess with the lever held in, there is nothing to stop those air bubbles travelling to the highest point, ie the resevoir.

 

[shoggoth80]

Got it bled out pretty well. There was a LOT of air in there initially. It feels much, much better now.
I'll try that cable tie trick though, just to make extra sure.
Now I get to EZ Out the busted rear brake cam lever bolt (I was a jackass and didn't pay attention while tightening it down).
Then hopefully, my battery isn't shot... as it's be a real beast trying to get it to start up. I haven't altered the timing or anything at all. So in theory, it should fire up. All I get is a annoying buzz when I try to use the electric foot... and the battery has sat on the bike for a while, so I really wouldn't be surprised if it was shot as well. Overall coming together ok though. I recovered the seat (backyard vinyl job, but it is still better looking than the seat cover that was one there). A couple small quirks to work out, and she should be back on the road again.

 

[rikusa]

brake dance

brake dance

A handy tip I picked up is to bleed the brakes as normal, then after nipping the bleed nipples back up, pump the lever several times until you feel a bit of pressure, even if the lever feels spongy, then on the last pump hold the lever in, then use a cable tie around the lever and handle bar to hold it in. Leave the cap on the master cylinder resevoir loose, put bike on side stand and turn bars so the resevoir is on the higher side, then leave bike for about 24 hours. Cut the tie, fit the resevoir cap back on, and you should find you have a good brake now. It`s worked for me really well in the past. I guess with the lever held in, there is nothing to stop those air bubbles travelling to the highest point, ie the resevoir.

The bubbles are smaller under compression and can move through smaller spaces. It's an old trick I learnt on Series Landrovers; bleed the brakes then jam the pedal down with a piece of wood overnight.

Get a big syringe and bleed from the calipers up. It's a racing trick from the same school that showed me how to weld a gas tank with gas in it and how to straighten a Velocette frame in a hotel bathroom doorframe with 2 car jacks and a hammer! Low budget racing; nothing is impossible!

 

[KEITH KRAUSE]

A handy tip I picked up is to bleed the brakes as normal, then after nipping the bleed nipples back up, pump the lever several times until you feel a bit of pressure, even if the lever feels spongy, then on the last pump hold the lever in, then use a cable tie around the lever and handle bar to hold it in. Leave the cap on the master cylinder resevoir loose, put bike on side stand and turn bars so the resevoir is on the higher side, then leave bike for about 24 hours. Cut the tie, fit the resevoir cap back on, and you should find you have a good brake now. It`s worked for me really well in the past. I guess with the lever held in, there is nothing to stop those air bubbles travelling to the highest point, ie the resevoir.

Does this method also work if you've already bled the brakes and squeezed the lever several times to achieve full pressure? I mean, is it somehow necessary to stop pumping AS SOON as you feel a bit of pressure and then tie the lever down? Can I just go out and tie the lever, loosen the cap and tilt the bars?
My brake bleeding method seems to work fine but I don't mind trying this over-night thing to remove any remaining bubbles.

 

[rickt]

Using a syringe

Using a syringe

The suggestion of using a syringe is a good one. I have bled many cycle brakes and spent painful hours trying to get a working system. I have access to medical supplies but you may be able to pick up a 50 ml plastic syringe at the drugstore or vet supply. Push the pistons all the way into the caliper - fill the syringe with fresh fluid and attach a short section of plastic tubing onto the syringe (the other end of the tubing should fit tightly over the bleeder valve) - remove the cap from the MC reservoir - gently force the fluid into the caliper and lines - after the fluid starts to fill the MC reservoir, watch for air bubbles to appear - when the bubbles stop, you can move to the next line, if you have one. I have found this method to work much better than the classical "squeeze the handle - loosen and tighten the bleed valve" method.

rickt

 

[shoggoth80]

Got the bike up and running with a fresh battery. Sounds like it always did. Although I did notice that my oil level dropped significantly, as it went from Full to Low in the interim. I think it's because I've installed a fresh oil filter, and it took a little circulating to get that area filled as well (same seems to apply for cars as well in my experience; new filter, increased qty. of oil. Though I did kick it over multiple times after doing so, perhaps only actual running creates enough pressure to seriously move the goo around).

I did notice some carb dripping, but it only did it when I had the bike upright. I tapped on the carbs a bit in an effort to get anything that might have been a little gummed up unstuck. When I last had it on the centerstand, no leaks. I really hope I can avoid carburetor work on this one. It's much harder when you cannot unbolt individual carb units like on my Kawasaki. And my intake boots might not survive if I took them off. They don't look horrible, but there is a small chunk missing from the far left flange. Doesn't seem to be enough to cause any air leaks, but enough to make me paranoid. I have never had the carbs off on this bike (and I still haven't figured out where I put my manual last).

Such is the nature of the beast though I suppose. I'll tinker more when I get more time.

 

[GKLENNY]

bleeding

bleeding

Hi ,some times minute air bubbles cling to the hoses,so before you start putting a thirty gallon drum of break fluid into the jam jars via your calipers (which you can ) work the break leaver nice and slow with the bleed nipples closed and observe the minute bubbles in master cylinder,then try bleeding in the normal way.Another method is to pressure bleed them by adapting a spare master cylinder cap to a bicycle type pump, tie the master cylinder break leaver back open the caliper bleed nipples and steadily force the fluid through the system,tighten the bleed nipples and bleed in the normal way hope this helps regards GKLENNY

 

[Zooks]

Sounds to me like there is air in the line. Bleeding the line is the best way to get rid of the air bubbles, no way around doing it. The process is a slow one. \\/

Could be worse. I've got a 6 tonne Dodge truck that I rebuilt the brakes on a few years back. That sucker took some time to bleed the brakes.