Front Brake Question

HappyHunter

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Howdy,
I have a 1982 Yamaha XS650. The front brakes did not work when I bought it. The lever felt normal but there was no brake action.

I pulled the caliper and it is not seized up. It looks like it might be usable. I put it back together and tried to bleed the brakes. The piston was real slow moving outward to engage the disc. I have no real brake feel. I also look in the fluid well while pumping the brakes and I see a stream of small air bubbles coming out of the two holes in the bottom of well. I'm thinking there should not be bubbles coming up out of there? Correct? Do I have leak somewhere? I do not see any fluid leaking anywhere.

Help please.....

Thanks,
HappyHunter
 
Sometimes..... sometimes... you need to pump the lever and just crack the banjo bolt open at the master cylinder.... because of the bars.. air can be trapped there... I've had this a couple of times on the buckhorns…. Did you remove and service the caliper slide..?
 
With the master cylinder level you can hope that eventually those small bubbles rising will be bled out. I actually tap lightly on the reservoir to encourage the bubbles to rise. Once the master cylinder is primed well enough to push brake fluid through the line go for the manual bleed at the caliper bleed nipple
 
Yes I did clean and lube up the slider. I do get fluid out the bleed nipple. I tapped a lot on the caliper and got lots of bubbles. They have stopped now. I will try tapping on the reservoir.

Thanks!!
HH
 
If you have the original "rototiller bars" sometimes you have to remove the master cylinder from the handlebar or loosen the bar clamps and rotate the handlebar way forward so the bubbles can all work their way out of the holes. Turning the forks full left with bike on the sidestand helps the angle also.
 
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Another thing to try is pump the brake several times and then tie the lever tight. Leave it over night. You may have to do this a few nights but eventually the air will rise up to the reservoir.
 
I had a heck of a time bleeding front brakes. Had flow and resistance on squeeze out of mc when I put my thumb over it, caliper was cleaned and rebilt. I just couldn't get resistance when it was all hooked up. I tried filling from caliper I tried tying the handle down over night. Everything was fine I just couldn't get it. I went to buy a brake vacuum pump at harbor freight, I heard was the answer. They were out of them. I wound up had to bring it to shop and paid 80$ I think it was to get my front brake back. I still don't know why I couldn't get it.
Cracking the banjo at mc as someone said sounds like a try.
 
Main thing you need to keep in mind in a fluid air will raise to the top. If the little return hole is not at the highest point of the system there is a good chance you will never get the air completely out.

Also if that little hole is plugged or blocked because the piston in the master is not returning all the way air will never get vented.
 
I used to think that but then realized that the return hole is unblocked when the lever is released not pulled.
It worked for me on my Rocket III, so I figured it would work elsewhere as well. I cannot get one screw to move on my Master cyclander in order to bleed the front brakes properly, so I used this method to success.
 
It worked for me on my Rocket III, so I figured it would work elsewhere as well. I cannot get one screw to move on my Master cyclander in order to bleed the front brakes properly, so I used this method to success.

Can't say I have any scientific proof as to why tying the lever down helps. I'm thinking that it has to do with the pressure compressing the air in the lines some how gives the air more "incentive" ,for lack of better term, to move up the lines and into the master. Where once you do release the lever and uncover the vent hole it has a better chance of getting out.

Bet someone could write a thesis on the process and get a degree in engineering from MIT on the subject! It could also be compared to the process of how divers can be killed by coming to the surface from a deep dive too fast.
 
@kshansen I wonder if you are on to it. The air does not leave the line while under pressure in the closed system. But, once the air has traveled up, when the pressure is released the hole is opened allowing the air bubbles to move into the reservoir. Just a thought...
 
@kshansen I wonder if you are on to it. The air does not leave the line while under pressure in the closed system. But, once the air has traveled up, when the pressure is released the hole is opened allowing the air bubbles to move into the reservoir. Just a thought...
I'm theorizing that the air under pressure changes it's properties more in relation to the brake fluid than the fluid itself does. Something like the air bubbles when squeezed down have a better chance to overcome the surface tension of the fluid and there for join together in bigger bubbles as opposed to fine bubbles closer to foam. Once they are a bigger bubble they would have more "power" to raise up in the fluid and have a better chance of working their way to the master.
 
About a week ago I replaced my front brake line on my ‘77. So starting out with a dry front line, I hooked up my Mighty Vac And proceeded to slurp 48 OZS. Through my brake system and never got a firm lever! Finally, I just put the cap back on the reservoir and walked away. For the next two days I would periodically go out in my garage and pump the handle while tapping the brake caliper, brake line and master cylinder with the plastic handle of a screwdriver. It just had to be micro bubbles in the system that needed time to work out because it fixed itself. Now I have a very firm lever feel.
By the way, since then I ordered a set of mechanics syringes. The next time I bleed brakes, I’m going to try the old reverse bleeding technique. I’ve never tried it before, but it sounds logical.
84B0D084-0E96-4CB4-AA67-84D255B73202.png
 
@kshansen I wonder if you are on to it. The air does not leave the line while under pressure in the closed system. But, once the air has traveled up, when the pressure is released the hole is opened allowing the air bubbles to move into the reservoir. Just a thought...
I'm theorizing that the air under pressure changes it's properties more in relation to the brake fluid than the fluid itself does. Something like the air bubbles when squeezed down have a better chance to overcome the surface tension of the fluid and there for join together in bigger bubbles as opposed to fine bubbles closer to foam. Once they are a bigger bubble they would have more "power" to raise up in the fluid and have a better chance of working their way to the master.
I used to be in the camp believing this was all voodoo BS..... but... there's lots of anecdotal evidence out there that says it does work.
Air is compressible... an air compressor has a fixed volume and increases pressure. In the brake system, the air is surrounded by fluid. So when we increase pressure, the volume of air is decreased... a lot. Big bubbles become small bubbles. Small bubbles can navigate small passageways easier... and also have less surface friction.
So yeah.... I've never tried it, but I can (now) see how tying the handle off could help.
 
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There is a lot of information in the Tech section on bleeding brakes.
Easiest way I have found with a totally dry system or otherwise: If you have rebuilt the caliper, you want the piston pushed all the way in on install. Less air to bleed out.
With everything hooked up, the MC needs to be level or slightly nose down on the hose end. Sometimes you can just turn the bars.
-Fill the Resv. about 1/2 full.
-Open the bleeder a good turn on the caliper, until you see fluid running out. Close it. Bleeder is on the top. Just wait for the fluid. May take a bit.
- The air in the system will rise to the top and into the MC but... Don't just pull the brake lever all the way in and don't pump it.
- Pull the brake lever just the slightest amount working the piston. If the lever adjustment is close, about 1/4 inch or less lever movement is all you want. The object is to allow the air bubbles in the line to come to the top and exit the MC thru the port. You will at first see a lot of big bubbles.
- When the bubbles get smaller, pull the brake lever fully in and let it out, slowly! Keep an eye on the fluid level in the Resv.
- The bubbles need help to exit the MC port. You will see a bubble just sitting at the top of the port. Using a zip tie, touch the bubble and it will let go and rise. No tapping needed. Don't stick anything down into the port, like a tooth pick! Keep the zip tie in the top of the hole and return to slightly moving the piston. Your working with the air in the very top of the system, around the piston, and allowing fluid to replace the air in the lower part that is rising to where your working.
Helping the bubbles to escape using the zip tie is really important.
- After a time it seems like there are no more bubbles. Pull in on the lever and let it out, slowly. You should feel a brake. Don't worry about the sponge. You should see a trail of small bubbles that may need help. Soon, as you pull the lever firmly and release, you will see a fog. You should have a good brake at this point. The fog is a sure sign very little air is left in the system. Usually the system will purge the remaining air on it's own.
It's not hard and not messy.
Just be sure to not let the MC resv. run dry while working, and easy on the lever. You don't what to force any air in the piston area, into the top of the brake line any further than it takes to work the piston a bit.
What do the steady pulls do? When it's time for the first pull, enough of the air should be out of the system to allow the filled caliper to push out against the rotor. Your not looking for a hard brake at this point, but if your close to getting one, so much the better. The second and later pulls are to put pressure on remaining air. It will show as small bubbles or fog.
Leave the system to set a bit and then check again for fog.
 
The front brake is a difficult system to set properly. I did my rear brake in 15 mins, I've been working on the front brake, on and off, for about a month now. I have tried many of the techniques described above. I have rebuilt the thing with new plunger kits twice and I am in the midst of setting it up and bleeding it again. I have come to the conclusion that technique and persistence are the key. The system is simple - hydraulic fluid pushed by a rubber plunger down a tube to activate a moving piston. If the seals are intact at both ends and at all connections, there is really nothing that can go wrong - except for air in the system. If it's not leaking and it's not working, it has to be air. I like Gary's reverse bleed technique that fills the calliper with fluid and forces it back up the line with a "C" clamp. I have done this a number of times and achieved at least some pulse at the piston. This time I am going to show more patience rather than looking for an immediate fix - lots of tapping of the calliper, line and reservoir, bleeding at the banjo and evenings spent with the lever tied back. I'll get the bastard or die trying. 5T swears by the MityVac so that is an option but give the advice offered above a good run before buying your way out. Eventually, it has to work.
 
".... I'll get the bastard or die trying." My Man! Yep, but the other ways can be messy. Say if your bleeding the brakes by Squeezing the lever, holding it and opening the bleeder, if timing is not perfect it will draw in air. and your never gona get it that way. The inlet on the caliper is on the bottom. The bleeder is on the top. If the resv. has fluid in it and you open the bleeder, fluid runs out past the piston, down the line/s, into the caliper. If you open the bleeder till you see fluid well up from the bleeder most of the work is done. But if the system has air in it between the end of the piston and caliper, a lot of fluid has to pass out the bleeder until the fluid pushes most of the air out. A case like this is where you work the lever lightly. That will push a small amount of fluid into the line but not so much lever movement the air your trying to get out at the piston is pushed back down the line. The Mighty vac is sucking the fluid and air down and out, with a lot of fluid. ( Like bleeding an auto MC on the bench before install.) The reverse process is pushing the air up and out.
The air in the caliper has to come to the bleeder, especially if the bike is on the side stand, well, for the RH caliper if you have duals but... So the only air in the system is in the line and around the piston. You can't believe how much air will come out if you touch the bubble in the port mouth with the zip tie. Agitate the air to rise by slightly working the piston, and you have to get the bubble to release from the MC port till you get the fog. Then you can really clamp down on the brake if you want to but. The brake will be good and become air free.
 
Howdy,
I have a 1982 Yamaha XS650. The front brakes did not work when I bought it. The lever felt normal but there was no brake action.
I pulled the caliper and it is not seized up. It looks like it might be usable. I put it back together and tried to bleed the brakes. The piston was real slow moving outward to engage the disc. I have no real brake feel. I also look in the fluid well while pumping the brakes and I see a stream of small air bubbles coming out of the two holes in the bottom of well. I'm thinking there should not be bubbles coming up out of there? Correct? Do I have leak somewhere? I do not see any fluid leaking anywhere.
Help please.....
Thanks,
HappyHunter

Hi 'Hunter,
single disk? If you twin your front brakes it's 4 times as difficult to bleed'em.
What worked for me and my son when we swapped our stock fabric brake hoses for stainless hoses
( you could do that too, it really improves the brake feel)
was to fill & bleed the brake lever then fill the calipers & brake lines with a syringe from the bottom up
via the bleed nipple.
Took my son half an hour to get his brakes bled. Took me half a day.
Sometimes it's just about the way you hold your tongue.
 
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