Rear brakes suddenly went soft.

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ScottMA64

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Hi guys, as I was going home in the typical stop and go traffic,
my rear brakes suddenly goes soft. When I got home I checked the fluid
and pads. Fluid looks full and pads still have plenty of meat. There are
no apparent leaks. When I get time I'll try bleeding 1st. What else could be
the problem?

Scott
 
ScottMA64 said:
Hi guys, as I was going home in the typical stop and go traffic,
my rear brakes suddenly goes soft. When I got home I checked the fluid
and pads. Fluid looks full and pads still have plenty of meat. There are
no apparent leaks. When I get time I'll try bleeding 1st. What else could be
the problem?

Scott
Click to expand...

Soft or spongey brakes probably means air in the system. When was the last time your fluid was changed? It may be time to just flush the system and start fresh with new fluid. It's possible that there was a pocket of air that finally made it to either end of the system, M/C or Caliper.
 
if your using the rear brake quite alot and it gets excessively hot (or binding on even) it will cause brake fade (boiling fluid),, as YZF RIDER NY says a fluid change first & see how it goes from there,,
 
I use both brakes concurently in stop and go traffic so I don't think the rears heated up anymore than usual. My 1st thought was air but I thought it was strange for it to happen all of a sudden. I've only owned the bike a cpl months, its an 04 with 16k on it. I dont know much history about the bike. I will def try and bleed them 1st.

Thanks guys!

Scott
 
ScottMA64 said:
I use both brakes concurently in stop and go traffic so I don't think the rears heated up anymore than usual. My 1st thought was air but I thought it was strange for it to happen all of a sudden. I've only owned the bike a cpl months, its an 04 with 16k on it. I dont know much history about the bike. I will def try and bleed them 1st.

Thanks guys!

Scott
Click to expand...

It's possible that the air was trapped "mid-line" and finally worked it's way down, or up.
 
I had the same problem. I bought a s/s braided line and installed it and bled the system. last a month, Im gonna rebuild the master cylinder. but for now im riding w no rear brake at all.
 
Hi Scott, a spongy or soft behaviour of the brake pedal, in my opinion (and also experience...), may depend on air bubbles or on something that doesn't work in the master cylinder's or calipers' (i.e. damaged gaskes). Another issue may reside in the brake fluid pipelines, infact the tube's braid could be teared by the the brake fluid's pressure as the tube gets older.

So, the solution may be one of the following:
- overhaul the master cylinder or the caliper
- substitute the brake fluid pipeline

I hope I have contributed ;)
 
Update: Hi guys, I FINALLY was able to get around to working on this problem again. I bought a rebuild kit for the rear master cylinder. I installed it and I still have the same problem. I spent a LONG time trying to bleed the lines but im not having any luck. I can hardly get any brake fluid out of either bleed valve, its almost like the cylinder simply isn't pushing the fluid through the lines. I don't have a leak anywhere that's apparent.

What else could the problem be?

Thanks!

Scott
 
ScottMA64 said:
Update: Hi guys, I FINALLY was able to get around to working on this problem again. I bought a rebuild kit for the rear master cylinder. I installed it and I still have the same problem. I spent a LONG time trying to bleed the lines but im not having any luck. I can hardly get any brake fluid out of either bleed valve, its almost like the cylinder simply isn't pushing the fluid through the lines. I don't have a leak anywhere that's apparent.

What else could the problem be?

Thanks!

Scott
Click to expand...

I would set up two lines, one to each side of the caliper. Crack both bleeders open and make sure the reservoir is full. Let the system "gravity" bleed for a little while. Also, before you do that, first pump the brake lever a few times, then hold it down, and crack the banjo nut at the Master Cylinder. Do this a few times to make sure it has been properly "bench bled".
 
save yourself the money on a rebuild kit and just do a rear reservoir delete, a few bucks for some clear tubing and done deal.

or just bleed your rear real quick to double check for air bubbles, it happens, and it only takes about 5 minutes to do and you can do it yourself really easily
 
ScottMA64 said:
Update: Hi guys, I FINALLY was able to get around to working on this problem again. I bought a rebuild kit for the rear master cylinder. I installed it and I still have the same problem. I spent a LONG time trying to bleed the lines but im not having any luck. I can hardly get any brake fluid out of either bleed valve, its almost like the cylinder simply isn't pushing the fluid through the lines. I don't have a leak anywhere that's apparent.

What else could the problem be?

Thanks!

Scott
Click to expand...
I take it you know the correct way to bleed the lines?
 
Yup, I know how to properly bleed brakes. :)

I ended up buying a hand pump. Even with the hand pump though, its barely sucking out any fluid, makes me think im either pulling in air somewhere or there is a blockage somewhere. I got it bled enough for the brakes to work but they are still on the spongy side.

Thanks for the help guys!

Scott
 
It sounds to me like your passage way out of the MC is blocked. If your old fluid sat in the MC for years without being relaced, there was probably some water in it and that may have coroded the exit hole. I think it is the best to take the MC apart and clean it and the holes very good and your braking should come back. If you find any corosion in the MC there's a good chance it may also be in the wheel cylinder as well. Rather than half-stepping it, you might as well do a good job and be done with it.
 
I believe you said this is a new to you bike - only a couple of months - and it is what - and 04? There is age here - but worse than that is the possibility that someone in the bike's past mixed the wrong chemicals as brake fluid. May have put some other type fluid in the brake system - maybe transmission fluid, or oil, or ...
These things are not compatible. There must be only brake fluid in the system. Mixing stuff can cause a destructive mixture that can "eat up" your seals. And that eaten up seal debris can clog lines and metering holes. It can be a mess.
If this is what it is only a complete rebuild with a purge of the system to remove traces of the old bad chemicals will do.

Your description made me thing of seals gone bad - mushy. Which is what mixing the wrong stuff results in.
Look at the fluid. Does it appear clear? Or does it appear milky or thick?

Another idea for you.
Good luck.
 
Also, I don't know if anyone actually follows the service manual, but it suggests replacing the lines every 4 years. I put SS lines on my '09 rather than replacing the OEM rubber.
 
I would remove the brake line from the rear caliper and pump the brake pedal to see if I get more fluid to flow. If so, your caliper is likely the problem. The rebuild kit should have taken care of any issues with it.
 
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