Rear brake failure

[Dialtapper]

Yesterday riding down a canyon road I felt the rear brake fade, then gone. Peddle would just bottom out, like no hydraulic pressure, and no rear brake at all.

After coming out of that canyon, about 15 miles of fairly straight riding, 65 MPH, no use of the brakes. Down into the next canyon the brake is working again, but I didn't trust it.

When I got home, fluid level is at the low mark, pads look maybe 40% worn.

2001 with about 6k miles.

Any ideas?

 

[dannymax]

Wonder if air could do that? When it failed did you pump it a bunch of times to try and get the pedal back?

 

[jfeagins]

What are you waiting for???????? Go out and BLAST some more canyon roads before the brakes completely wear out!!!

KIDDING. Seriously, it sounds like it's time for some rebuild kits. If it were mine, I'd be putting kits in the master cylinder AND the caliper. I'd be doing both front and back brakes too. And changing the fluid in the clutch side at the same time, if this hasn't been done yet this year.

 

[one2dmax]

I had the exact same thing happen a few years ago while blasting the pig trail in Eureka Springs. About shit myself since I was turning and burning at the time. Almost no warning when it finally went. Took about 30 minutes for the brakes to cool down enough to work again.

BUT, that happened from extreme brake use. Some of the guys here can attest to how much workout I can give a bike. At the time was running with 2 ZX10's and 1 FZ1. Was the only vmax crazy enough to keep up.

I'd say to examine your pedal and make sure you don't have a bit of preload applied. It sounds simply like you overheated them and no other problem exists. You may be able to verify this by looking at the paint near where the center carrier and the rotor surface come together. It may have discolored it at that area.

 

[Dialtapper]

Wonder if air could do that? When it failed did you pump it a bunch of times to try and get the pedal back?

Ya, pulled over when we came out of the first canyon, pumped the hell out of it, no joy, dead.

My first thought was it was bypassing in the cylinder, but it came back. These things don't heal themselves.

My other thought, got hot and failed? Been on this ride many times, never happened before.

 

[Dialtapper]

I had the exact same thing happen a few years ago while blasting the pig trail in Eureka Springs. About shit myself since I was turning and burning at the time. Almost no warning when it finally went. Took about 30 minutes for the brakes to cool down enough to work again.

BUT, that happened from extreme brake use. Some of the guys here can attest to how much workout I can give a bike. At the time was running with 2 ZX10's and 1 FZ1. Was the only vmax crazy enough to keep up.

I'd say to examine your pedal and make sure you don't have a bit of preload applied. It sounds simply like you overheated them and no other problem exists. You may be able to verify this by looking at the paint near where the center carrier and the rotor surface come together. It may have discolored it at that area.

I was replying when you posted this.

Don't think I was on the breaks any more than usual.

The rotor does look like it got hot, it's dark and there is discoloration.

But why would the pedal louse all pressure? Fluid hot enough to loose its viscosity?

Did you do anything or did it just cure itself?

 

[95spfldmax]

I had a similar experience not with the brakes but the clutch......similar systems.....climbing Mt Washington, NH just short of the summit and clutch disappeared......enjoyed the view and came back to the bike an hour or two later the clutch was fine. My system was low too, overheated and came back by itself. Definitely have to keep the proper volume of fluid in there.

 

[jfeagins]

Brake fluid can get hot enough in there to boil. When it boils, the air vapor will not compress like the fluid, and the brake pedal will go doooown. As the brake fluid cools, the air vapor is reabsorbed and pedal returns.

I don't know, but maybe older fluid can boil easier, and that'd explain why this is the first time it has happened to you in the same stretch of road.

At any rate, I'd be rebuilding and changing all the fluid if it were mine - cheap life insurance.

 

[one2dmax]

Change the fluid is all I personally think it may need. Gets the built up water out of the fluid (which does absorb water). On mine it was a slight change in riding habit (a little less rear brake) and swap to Dot 5.1 (non synthetic and higher boiling point).

DO NOT OVERFILL!!!

 

[Dialtapper]

Change the fluid is all I personally think it may need. Gets the built up water out of the fluid (which does absorb water). On mine it was a slight change in riding habit (a little less rear brake) and swap to Dot 5.1 (non synthetic and higher boiling point).

DO NOT OVERFILL!!!

Thanks Sean, the fluid looked like caramel, I changed it to Dot 5.

Found the reservoir cap cracked from one side to the center, does anyone think that might have had something to do with it?

 

[Traumahawk]

Couldve heated up....expanded, and started sucking air a bit....or atleast not allow pressure to build.

 

[m-cman]

If you changed to DOT 5 (not 5.1), hope you flushed the system COMPLETELY. DOT 5 is silicone based and not compatible with any other fluids. It was used in Harley's for several years but I heard they have returned to normal fluids. It doesn't eat paint but that is the only advantage I am aware of.

 

[Bill Seward]

Bet there was a bit of absorbed water in the fluid, which turned to very compressible steam when the brake fluid got hot from vigorous riding. I always buy brake fluid in small cans - costs more, but I don't like keeping fluid that has been opened, as I have concerns that unless sealed well, it will absorb water from the air. Most people will open a can of fluid to top the reservoir up, screw the cap back on it - and forget about it for a year or more till they need it again. This time will let the water be absorbed into the fluid, even with the cap screwed on.

Just my opinion.

 

[Fire-medic]

Thanks Sean, the fluid looked like caramel, I changed it to Dot 5.

Found the reservoir cap cracked from one side to the center, does anyone think that might have had something to do with it?

Only in that water could more-easily enter the reservoir. Caps are vented.

Change fluid at the end of your riding season, no water in the system to corrode things over the winter, and in the spring, one-less thing to do.

 

[Dialtapper]

If you changed to DOT 5 (not 5.1), hope you flushed the system COMPLETELY. DOT 5 is silicone based and not compatible with any other fluids. It was used in Harley's for several years but I heard they have returned to normal fluids. It doesn't eat paint but that is the only advantage I am aware of.

I used DOT 5. I have a pneumatic brake bleeder, I sucked everything out with that.

So DOT 5 is not a higher temp boiling point? $4.00 for a quart of DOT 3, $15.00 a pint of DOT 5, what am I paying for besides the purple color?

 

[Diablotin]

I used to have the same issue when using the rear a bit more. A good bleeding made it better. It totally disappeared after putting a 4 pistons caliper. Not sure how it can be linked.

Sent from my GT-I9100 using Tapatalk 2

 

[MaxMidnight]

It sounds like a classic case of brake fade when the water in the fluid boils, turns to steam (which is a gas) and which can be compressed so you loose the pedal.
As brake fluid ages it absorbs water - the higher the moisture content the lower the B.P. (155 C for Dot 4)

Most likely cause is too much reliance on the back brake over the front.

There is no benefit from using Dot 5 and several disadvantages: cost (but you know that already), not compatible with Glycol based fluids (you now know that) and moisture isn't absorbed into the fluid so it will pool in the system which will become more susceptible to corrosion (something for the future?). Apart from that...

Have a read of this

 

[Dialtapper]

It sounds like a classic case of brake fade when the water in the fluid boils, turns to steam (which is a gas) and which can be compressed so you loose the pedal.
As brake fluid ages it absorbs water - the higher the moisture content the lower the B.P. (155 C for Dot 4)

Most likely cause is too much reliance on the back brake over the front.

There is no benefit from using Dot 5 and several disadvantages: cost (but you know that already), not compatible with Glycol based fluids (you now know that) and moisture isn't absorbed into the fluid so it will pool in the system which will become more susceptible to corrosion (something for the future?). Apart from that...

Have a read of this

Excellent article, thank you.