losing brakes

[Dexx]

Two weeks ago I replaced the rear tire and put progressive springs in the forks. Also replaced the rear brake pads while I had everything apart. To compress the pistons in the caliper, I removed the bolt from the rear master cylinder to relieve pressure. Cleaned all brake parts, and bled the line following the factory manual (rear caliper, front caliper, metering valve, in that order).

 

Around town the brakes work fine, but if I don't use them for awhile out on the road get no action from the peddle. It is very soft and depresses quite a ways with no stopping action from the rear/front left. If I 'pump' the peddle it returns enough to stop the bike with just the peddle. The front right is having no problems. I'm not sure what to look at next. It seems to me that if they start out tight and work around town that it wouldn't be the master cylinder, and it can't be brake fade from a misaligned pad heating up because it affects both calipers. Any ideas?

[capn eddie]

I had the same thing when i first got my bike , bleed the brakes had good pedal go for a ride park it overnight and pedal goe's down. :confused24:The problem is there is still air in the system, belive me i know. :whistling:Put bike on side stand, get some speed bleeders and bleed it again do the back first then the front left with the forks turned to the right( gets bleeder to a high point) and then bleed the metering valve. There is alot of air traped in the valve so you will have to bleed this alot. Took me two times to get the air out. Now my pedal is hard all the time. Just about drove me crazy the first time i bleed mine and the next day it had no pedal. Speed bleeders is the way to go when bleeding the brakes, you can do it by yourself , get the bleeder bag also makes for a easy job. Good luck and if it doesnt work the first time let it sit overnight and do it again the next day. Worked for me. PS www.speedbleeder.com Took about a quart and a half of brake fluid. bleeder # sb8125l

Edited June 15, 2008 by esaffley

[bongobobny]

Yup, that's exactly what it sounds like to me, too, air still in the line. Or, could be your bleeder is not tight or leaking, or a brake line is a little loose. Check everything for signs of seepage. Small leaks will maks the pedal spongy and require pumping up, and they will still fade after a while...

[Condor]

On the '89 Mark II there is another bleeder valve located in the front brake line at the top of the loop just to the right of the ignition switch. What's happening is that any compressed air suspended in the fluid under pressure is expanding overnight, and rising to the top of the loop, causing the sponginess. I'd also bleed the front caliper first and then the rear. Some may disagree with this, but I've always heard you bleed the one furthest (front) caliper away from the master first, and then the closer (rear) one.

[Dexx]

On the '89 Mark II there is another bleeder valve located in the front brake line at the top of the loop just to the right of the ignition switch. What's happening is that any compressed air suspended in the fluid under pressure is expanding overnight, and rising to the top of the loop, causing the sponginess. I'd also bleed the front caliper first and then the rear. Some may disagree with this, but I've always heard you bleed the one furthest (front) caliper away from the master first, and then the closer (rear) one.

 

This is where I'm getting confused by the whole thing. My experience with air in the lines on anything is sponginess all the time. This starts out firm and goes soft after I haven't touched the brakes for a few miles. I've got the speed bleeders on the way, but they probably won't get here in time to save the camping trip this weekend that I have been planning all year. Hopefully I get lucky and they will help solve the problem, If it turns out to be the master cylinder, I'll have to wait a week for parts.

[hdroyer]

I read some where that if you loosen the cap bolt on the rear master and shim the peddle down putting pressure on the system over night this forces the air out.

Dale

[Condor]

This is where I'm getting confused by the whole thing. My experience with air in the lines on anything is sponginess all the time. This starts out firm and goes soft after I haven't touched the brakes for a few miles. I've got the speed bleeders on the way, but they probably won't get here in time to save the camping trip this weekend that I have been planning all year. Hopefully I get lucky and they will help solve the problem, If it turns out to be the master cylinder, I'll have to wait a week for parts.

 

As the brake fluid heats up a little the air expands a lot and causes the sponginess. That's why it's so dang important to get all the air out of the system. Bleed 'm.....

[Condor]

I read some where that if you loosen the cap bolt on the rear master and shim the peddle down putting pressure on the system over night this forces the air out.

Dale

 

I've heard that too Dale, but.... I don't see where putting pressure on the fluid would cause the air to leach out of the system. I can see the air volume getting smaller under pressure or getting suspended in the fluid. MOF by pushing the master piston in, the expansion opening that would allow air to escape from the lines is closed off. I still think a small amount of air is trapped at the top of the brake line and causing the problem.

Another area that should be considered is how old was the 'new' brake fluid used when the brakes were bled?? Old stuff that's been laying around the garage for a while will absorb moisture. That moisture will boil when brakes are applied and 'steam' will expand and cause the brakes to get spongy. The fluid may have a 400deg boiling point, but the suspened water still boils a 212degs at sea level. When the fluid is under pressure the water BP will go up, and not start boiling until a higher temp is reached, but release the pressure off the system and it goes back the 212. Kinda like taking the radiator cap off, and the coolant going balistic...

[Yammer Dan]

The method of pulling handle in against handlebar and tying it there with cap loose works great on clutch. Haven't tried it on brakes. But it will bleed the clutch when it is being stubborn.

[Dexx]

Thanks guys, I had my doubts due to experience with other vehicles, but with the speed bleeders in I got A LOT more air from the front caliper and the metering valve. still seems like a little more than a one man job, even with my home made "i.v. drip" keeping the master cylinder filled , but went out for a good forty mile ride afterward and everything seems good. If I ever buy another bike the very first thing I'm doing is putting speed bleeders on it. Really appreciate the help.

[bongobobny]

Well, then , if a 40 mile trip wasa OK then a little longer trip. like over to my place some time, should be in order...

[capn eddie]

Dexx, glad to here you got it done ,like i said had same thing with mine, the guy's here on this site told me about the speedbleeders worth the money and thats how i knew the air was still there, been there done that. now go out and ride that puppy.

 

 

 

 

 

 

[timgray]

Are the speedbleeeders they mention at the website right? does all yamaha's use the same size from my old 83 to the newest 09 rsv?

 

It seems that my bike caught the soft pedal cold this winter. took a first ride after reassembly from the paintjob and no rear brakes until I pump them up.

[bongobobny]

I'm about 99% positive they are the same size...

[rhncue]

I've heard that too Dale, but.... I don't see where putting pressure on the fluid would cause the air to leach out of the system. I can see the air volume getting smaller under pressure or getting suspended in the fluid. MOF by pushing the master piston in, the expansion opening that would allow air to escape from the lines is closed off. I still think a small amount of air is trapped at the top of the brake line and causing the problem.

 

Another area that should be considered is how old was the 'new' brake fluid used when the brakes were bled?? Old stuff that's been laying around the garage for a while will absorb moisture. That moisture will boil when brakes are applied and 'steam' will expand and cause the brakes to get spongy. The fluid may have a 400deg boiling point, but the

suspened

water still boils a

212degs

at sea level. When the fluid is under pressure the water BP will go up, and not start boiling until a higher temp is reached, but release the pressure off the system and it goes back the 212. Kinda like taking the radiator cap off, and the coolant going balistic...

 

This is the cause for sure. As soon as I read the problem I knew it was moisture in the brake fluid but continued reading the comments and then seen that you answered it correctly. Brake fluid absorbs moisture from the air and new fluid should be discarded after a short while after the container has been opened.

 

Dick