Brakes Failed--What Happened?

[Trinorman]

The other day on a ride I totally lost my linked front and rear disc (1984 V65SP).  We were in the mountains, temps around 90, riding the twisties and were descending when I noticed the brake pedal went through a longer range of travel and had zero stopping power.  No hydraulic pressure at all.  It had been working normally up to that point.  I never felt that I was using the brakes particularly hard or that often.  The right front disc was all that I had.  Rather than continue on the mountain roads, I got on a nearby freeway to ride home.  About 10 minutes later I had to brake for traffic and all brakes were normal again.  I kept testing them all the way home and had no problems—braked as it should.

At home, a check of the reservoir showed it was full.  The master cylinder was perfectly dry, no sign of leakage.  No sign of leakage along any hydraulic line which are the original (I think) rubber lines.  The only issue I noticed was that there was no play between the brake pedal linkage arm and the master cylinder piston as there should be.  I adjusted that to the specs in the manual which took 2 full turns on the linkage rod to bring into spec.

So my question is, any idea what caused the loss of brakes?  Could the above maladjustment have caused it?  Any help appreciated as I wouldn’t want that to happen again when I might really need all brakes!  The bike has about 14,000 miles on it, the last 7000 or so since I've owned it with no brake related issues up til now.

Thanks for any help.

Chris

[fotoguzzi]

I would start by replacing the rubber lines with something new..I bet there was a big bulge in the line blowing up like a balloon instead of pressing on the pads.. lucky it didn't split and wash all over your tires.

[Kent in Upstate NY]

Over heated brakes? Old water contaminated fluid? Stuck calipers?  Check and flush your system and fill with fresh fluid might be a place to start.

[Triple Jim]

If your no clearance between pedal and MC situation caused the bleed hole in the MC to remain covered, any warming up of the system could have caused the brakes to drag.  Eventually the fluid would boil and you'd have vapor in the system that would feel as you described until things cooled off again.  I'm not sure this is what happened, but it's possible.

[pehayes]

If your no clearance between pedal and MC situation caused the bleed hole in the MC to remain covered, any warming up of the system could have caused the brakes to drag.  Eventually the fluid would boil and you'd have vapor in the system that would feel as you described until things cooled off again.  I'm not sure this is what happened, but it's possible.

 :1:  Same thing happened on Regina's V65C.  Figured it out when the rider behind told us the brake light was on constantly indicating internal pressure.  Remove the linkage and make sure the piston of the MC is clean outside of the seals and that the seal allows the piston to slide easily.

Patrick Hayes
Fremont CA

[DavidR8]

Did you smell anything?
If the brakes were hot enough to boil the fluid I'd bet you'd smell the unmistakable odour of cooked brake pads.


Sent from my iPhone using Tapatalk

[Zoom Zoom]

First, how old is the brake fluid? The description you describe sounds like the fluid has absorbed lots of water. I would begin with that. If it's old replace it.

Second, what Photoguzzi said.

John Henry

edit: I would, at the very least, take a very close look at the rubber lines for cracks, even if all you do is replace the fluid. Being that brake fluid is hygroscopic, my money is still on that as the first place to look.

[Kiwi_Roy]

You were having too much fun and boiled the fluid 

[Trinorman]

Thanks everyone for all the tips.  DavidR8, never any smell nor any indication brakes were dragging.  Can't hurt to replace the fluid and make sure the piston is moving freely as Patrick suggested.  Maybe some SS hoses in my future too. 

[Scott DeRoss]

The other day on a ride I totally lost my linked front and rear disc (1984 V65SP).  We were in the mountains, temps around 90, riding the twisties and were descending when I noticed the brake pedal went through a longer range of travel and had zero stopping power.  No hydraulic pressure at all.  It had been working normally up to that point.  I never felt that I was using the brakes particularly hard or that often.  The right front disc was all that I had.  Rather than continue on the mountain roads, I got on a nearby freeway to ride home.  About 10 minutes later I had to brake for traffic and all brakes were normal again.  I kept testing them all the way home and had no problems�braked as it should.

At home, a check of the reservoir showed it was full.  The master cylinder was perfectly dry, no sign of leakage.  No sign of leakage along any hydraulic line which are the original (I think) rubber lines.  The only issue I noticed was that there was no play between the brake pedal linkage arm and the master cylinder piston as there should be.  I adjusted that to the specs in the manual which took 2 full turns on the linkage rod to bring into spec.

So my question is, any idea what caused the loss of brakes?  Could the above maladjustment have caused it?  Any help appreciated as I wouldn�t want that to happen again when I might really need all brakes!  The bike has about 14,000 miles on it, the last 7000 or so since I've owned it with no brake related issues up til now.

Thanks for any help.

Chris

The other day on a ride I totally lost my linked front and rear disc (1984 V65SP).  We were in the mountains, temps around 90, riding the twisties and were descending when I noticed the brake pedal went through a longer range of travel and had zero stopping power.  No hydraulic pressure at all.  It had been working normally up to that point.  I never felt that I was using the brakes particularly hard or that often.  The right front disc was all that I had.  Rather than continue on the mountain roads, I got on a nearby freeway to ride home.  About 10 minutes later I had to brake for traffic and all brakes were normal again.  I kept testing them all the way home and had no problems—braked as it should.

At home, a check of the reservoir showed it was full.  The master cylinder was perfectly dry, no sign of leakage.  No sign of leakage along any hydraulic line which are the original (I think) rubber lines.  The only issue I noticed was that there was no play between the brake pedal linkage arm and the master cylinder piston as there should be.  I adjusted that to the specs in the manual which took 2 full turns on the linkage rod to bring into spec.

So my question is, any idea what caused the loss of brakes?  Could the above maladjustment have caused it?  Any help appreciated as I wouldnÂ’t want that to happen again when I might really need all brakes!  The bike has about 14,000 miles on it, the last 7000 or so since I've owned it with no brake related issues up til now.

Thanks for any help.

Chris

First indication of the master cylinder going.

[pete roper]

When were the brakes last bled?

When were the brake lines last replaced?

When was the master cylinder overhauled?

The machine is forty or so years old. One would hope it isn't still running around on its original brakeware!

[normzone]

First indication of the master cylinder going.

In my admittedly brief tenure as a service station mechanic (2 years), I saw multiple automobile master cylinders go out, with something similar being the failure mode. The customer would be sitting at a stoplight and the pedal would slowly go to the floor. It would be fine when you hit it again.

Or rather, the last warning before the failure. Usually they'd hint like that multiple times and then fail altogether.

I had one do just  that on me in the service station parking lot as I was moving it to where I was going to work on it. The owner got it there with only zero stops left in it.

[wirespokes]

I don't see how a brake line could be bad, loose ALL pressure, and then a little while later, be ok again. I say "no way!" to this one.

It's one thing for a master cylinder to slowly "go to the floor", yet pump up, then eventually fail, but quite another to completely fail, then come back again. I wouldn't give this explanation credence either.

Old fluid - yes, this makes sense! Brake fluid can magically pull in water through the closed brake system. Water boils at a much lower temp than brake fluid, turns to gas, and does nothing to activate calipers. The master cylinder stroke isn't long enough to compress the water vapor.

When my master cylinder was too tight, the brakes dragged, eventually bad enough the bike wouldn't overcome them. Perhaps in this case they weren't able to drag badly enough, but that was sufficient to boil the brake fluid and cause that effect. Sounds possible to me.

It's best changing the brake fluid yearly due to the possibility of entrained water. If it's dark colored, definitely change it. It's cheap, and fresh fluid works better than old - it's an easy way to better braking.

[Huzo]

I don't see how a brake line could be bad, loose ALL pressure, and then a little while later, be ok again. I say "no way!" to this one.

It's one thing for a master cylinder to slowly "go to the floor", yet pump up, then eventually fail, but quite another to completely fail, then come back again. I wouldn't give this explanation credence either.

Old fluid - yes, this makes sense! Brake fluid can magically pull in water through the closed brake system. Water boils at a much lower temp than brake fluid, turns to gas, and does nothing to activate calipers. The master cylinder stroke isn't long enough to compress the water vapor.

When my master cylinder was too tight, the brakes dragged, eventually bad enough the bike wouldn't overcome them. Perhaps in this case they weren't able to drag badly enough, but that was sufficient to boil the brake fluid and cause that effect. Sounds possible to me.

It's best changing the brake fluid yearly due to the possibility of entrained water. If it's dark colored, definitely change it. It's cheap, and fresh fluid works better than old - it's an easy way to better braking.

You've got it!

[Mike Tashjian]

Boiling brake fluid is what gives the no brakes feeling.  Lacking specific information it is easy to guess multiple causes all of which are plausible.  This should be a good reminder that you have do your proper maintenance as your bike ages, if you want to ride safely.  I like to make a chart and follow along with all maintenance done, charted with time and or mileage.  Especially if you have more than one bike.  This lets me know at a glance the last time the air cleaner was changed or brake pads changed, etc.  Time rolls along and I forget easily, so the chart is an easy accurate reference.  Mike 

[Chuck in Indiana]

^^^^ Me, too. I keep a log on each machine, and do an "annual inspection" each year. The guy that "don't fix nothin that ain't broke" is riding a machine that's ready to break. <shrug> Fixing stuff on the side of the road is not only a pain, it's expensive.

[Sheepdog]

Old brake fluid/hoses plus a more complex master cylinder/proportioning valve arrangement are a bad mix. I think I would replace hoses/fluid, clean the calipers and install new cups, and flush the master cylinder. Do the hand brake caliper, too. I always err on the side of caution with brakes...

[Scott DeRoss]

I don't see how a brake line could be bad, loose ALL pressure, and then a little while later, be ok again. I say "no way!" to this one.

It's one thing for a master cylinder to slowly "go to the floor", yet pump up, then eventually fail, but quite another to completely fail, then come back again. I wouldn't give this explanation credence either.

Old fluid - yes, this makes sense! Brake fluid can magically pull in water through the closed brake system. Water boils at a much lower temp than brake fluid, turns to gas, and does nothing to activate calipers. The master cylinder stroke isn't long enough to compress the water vapor.

When my master cylinder was too tight, the brakes dragged, eventually bad enough the bike wouldn't overcome them. Perhaps in this case they weren't able to drag badly enough, but that was sufficient to boil the brake fluid and cause that effect. Sounds possible to me.

It's best changing the brake fluid yearly due to the possibility of entrained water. If it's dark colored, definitely change it. It's cheap, and fresh fluid works better than old - it's an easy way to better braking.

Just replaced the master cylinder on my Vintage. It went out came back more than once. Changed fluid and other things eventually replaced the master and all is fine.

[Pop]

Sounds so familiar. My 84 V65 did that to me up in the adorondiaks. It was a combination of sticky plunger in the master cylinder, old fluid , and spongy break lines. It was the one front brake and down shifting from Lake Placid to base camp in Northfield ( just west of Warrensburg) fun.
Pop