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Discussion Starter · #1 ·
Hi people,
I have a 2004 yamaha v star 1000. Got it a month and a half ago. Love it!
The rear brake was ok until it just happened out of the blue, not sure how, but the rear brake became spongy.
Here it what happens:
First time i brake, the lever goes all the way down and doesnt brake properly
Second time i brake, it brakes much better but still not perfect...
Third time i brake it works great! just like the way it should be.
Feels like i have to "pump it" few times in order to make it work properly.

So, i took it to the mechanic, he changed the fluid, and said there's no problem with air coming out... and obviously no problem with the fluid.

Does anyone have a clue what could it be?
Did it ever happened to anybody before?
Any comments and info about this would be highly appreciated!
Thanks so much!!!
Z
 

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Did you or the mechanic check the hoses very closely? There could be a weak spot in one. It does sound like air in the line though. And the master cylinder is ok, right?
 

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Discussion Starter · #4 ·
The mechanic said it 'might' be the hose, he is not sure therefore he wants to replace it. I dont want to replace anything im not sure about especially when he wants to charge me about $200 for this which to me sounds like mad expensive.
The cylinders seem OK. They dont look bent nor have scratches on them as a sign for bends or dents.
 

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You can change the hoses yourself if you are comfortable bleeding the brakes and getting all the air out. It is not that hard to do. It would be a good upgrade to change to braided brake lines. It would be alot cheaper to buy them yourselves and change them yourself. If you are comfortable doing it.

If there is a problem with a hose, it could burst while you are ridding and that would not be good. If it is the master cylinder, you could suddenly lose brakes there also. It could also dump brake fluid on your back tire. If it is the master cylinder and it goes out completely, then, you would lose your rear brakes also.
 

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The mechanic said it 'might' be the hose, he is not sure therefore he wants to replace it.
What qualifies that guy to be called a "mechanic" ??

Is the hose not (pretty much) visible over it's whole length so that it can be inspected??

And what kind of malfunction in a hose could cause the symptoms you describe......without also causing loss of fluid ??

I think he is full of :horse:
 

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I have seen (very rarely) hoses that were old or had a flaw have a soft spot (for lack of better term). The hose will flex a lot more than it should. I have seen an old one fail and I was ridding with a buddy about 12 years ago and his two year old bikes rear hose started shooting out fluid. It looked like an air bubble or something was in the rubber and it just gave way over time. When he replaced the line, he was amaized how much better the rear brake felt. He never realized he had a problem. He just thought that was the way it was supposed to be.

I am not saying that is his problem. Just a possibility. It does sound like his mechanic isn't doing much trouble shooting. I am with you in that the master cylinder should be looked at closer.
 

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it just sounds like air in the line, just bleed them and see what happens. when the mechanic changed the fluid and rebled them, he might of introduced aiTr back in to it. there is a way to bleed the brakes by yourself and i will guarentee there won't be any air in the line. the rubber part of the line could also be expanding when the lever is pressed which could cause your spongy brakes
 

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Discussion Starter · #10 ·
The mechanic did the bleeding, but there was no change in the sponginess feel. Its still the same...

By the way i checked the hose myself to make sure it looks good. It is mostly visible, and looks great.
 

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First time i brake, the lever goes all the way down and doesnt brake properly
the rubber part of the line could also be expanding when the lever is pressed which could cause your spongy brakes
That is NOT a symptom of a bulging rubber line.....nor is it a symptom of air in the line (unless there is a LOT of air and then it wouldn't go away with subsequent operations AND then return later).

:roll:
 

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it could be the master cylinder. it only takes a little air in a brake line to cause problems. a brake system is a pretty simple system, so it shouldn't take to much to figure out. easy rider, why do you think its the master cylinder? i want to see if you can explain it
 

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easy rider, why do you think its the master cylinder? i want to see if you can explain it
Oh, really? What's the point?
I have had them fail and rebuilt a couple so I know how they work.
This ain't my first trip to the rodeo!

The rod has a one-way piston seal on it. When moved one way, the edges of the piston-seal seal against the inside of the cylinder and makes pressure in the line. When it moves back, if any vacume develops it sucks fluid to the front side of the seal out of the reservoir to keep the pressure side full. It works like the leathers on an old-fashioned water pump.

SO.....if that little one-way pump seal wears out or gets warped or gets a speck of dirt stuck on the edge, then it won't seal and when you push on it, the fluid leaks PAST the seal back into the reservoir and you get.....NO PRESSURE. Sometimes with repeated operation, the little piston WILL finally seal and you get pressure again.

The Kawasaki master cylinder that I eventually had to replace had TWO seals on the push rod......such that if the main one failed, the second one would "catch" later in the stroke and give you good firm brakes......just with a LOT longer stroke than usual.

Is that what you wanted ??

To recap: When a brake pedal suddenly "goes to the floor" AND there in no fluid loss anywhere in the system and nothing is mechanically broken, the master cylinder is the "usual suspect". It can't hardly be anything else.

Maybe I should say that it has been 10 years or so since I've seen the inside of a master cylinder so it's entirely possible that some have a different "valving" arrangement now but whatever it is physically, it has to push in one direction and "suck" in the other. :bluethum:
 
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