V. hot brake caliper

[docc]

I like the old docc better.

 

Yeah, sorry. It just seems you two spend a lot of ink going at one another rather than the issue at times. I don't think you're breaking any rules ( I'm not sure there are any), yet it does get annoying when the tone remains somewhat condescending. Maybe I misread as tone is an awkward thing to convey in this medium.

 

I've learned a lot from both of you and do appreciate the effort that goes into the input. It's sad to say in way, but my Sport would not be running it weren't for this forum.

[Guest ratchethack]

It's high time you guys took your pi&&ing contest somewhere else.

Take it easy, Docc. It's not as serious as all that. . .

 

Or BFG's likely to whack you upside the head with that big walloping brake lever shillelagh o' his.

[dlaing]

Take it easy, Docc. It's not as serious as all that. . .

 

Or BFG's likely to whack you upside the head with that big walloping brake lever shillelagh o' his.

Shilelagh, the "peacekeeper" for bodgers who can't get their hands on guns!

[Martin Barrett]

 

Leafman is right about the unintentional foot pressure on the pedal being another possible cause. Others have admitted to that habit, especially certain people with policemen's feet. I don't ride with my foot that far forward so I'm pretty sure it wasn't the cause here.

 

Which boots were you wearing - Altberg lace ups or those nice climbing pumps? Having followed you whilst you were wearing your pumps. I did notice very deliberate balls of feet on pegs and move foot forward to brake, differing from my Charlie Chaplin esq style. So I also don't think that would have been your problem (mine was sticky pivot not policeman's feet).

[txrider]

Not to add to any dissension here but I think docc has a valid point.

[Guest ratchethack]

Not to add to any dissension here but I think docc has a valid point.

Point taken.

 

This might be a perfect place to point out wot I b'lieve many may still be missing here.

 

If we take Leprechauns and policeman's splayed feet resting on the brake lever out of consideration -- you'd think these would be pretty obvious, wouldn't you?? There are far more common, IMHO, serious, yet subtle and insidious causes of rear brake drag, which result in the aforemetioned heat/drag cycles, potentially overheating components to the point of loss of rear braking altogether, and even locking the brake whilst underway.

 

I refer again, of course, to the dastardly and pernicious work of the *Big 3*:

 

1. air in the brake fluid

2. water in the brake fluid

3. an accumulation of brake dust/road grunge betwixt brake piston and caliper

 

It seems that many have difficulty imagining how or why the most dastardly *Big 3* would ever be much of any concern.

 

Please allow a hypothetical scenario.

 

Assume (as is the case in all rear brakes with any appreciable miles on 'em) that there is some accumulation of the most dastardly *Big 3* in YOUR rear brake. There most certainly is in my brake right now, though I've taken the usual precautions to minimize each and have done so with a high degree of confidence ever since I noticed the especially unusual vulnerabilities of the "Frontbottom" P32B Brembo. Without assurance that these precautions are in place, the following can happen:

 

1. Normal brake use heats up rotor, pads, pistons and caliper normally. Water trapped in the powerfully hygroscopic brake fluid is converted to steam, expanding dramatically. Air trapped in the high points of the caliper likewise heats and expands dramatically. Between applications of the brake, gunk betwixt brake pistons and caliper prevents the pads from retracting normally, causing increased heat due to dragging pads.

 

2. Heated and expanding air and steam in the caliper push brake fluid up the brake line and through the open relief port at the master cylinder, filling up the brake reservoir.

 

3. The next time the rider applies the rear brake, suddenly, there's less firmness felt. He's now pushing against air and water vapor in the line and caliper. Since air and water vapor (steam) are far more easily compressible than air in the fork due to the extremely powerful leverage of the master cylinder, we have a problem here. Instead of brake fluid, which is nearly completely incompressible, our rider is now pressing on an air/steam spring with his rear brake lever, and a very weak one at that.

 

4. The brake lever fails to return to its normal position against the stop cam due to inadequate lube of the brake lever pivot. This keeps the relief port closed.

 

5. With the relief port closed, increasing pressure from the snowballing heat/drag cycle at the caliper has nowhere to go. The expanding hot gases in the caliper push harder and harder against the pistons, and the pads drag harder and harder on the rotor. More heat. More expansion of air and water vapor. More pressure.

 

6. The rider either notices his brake is dragging or he doesn't. He either pulls over or he doesn't.

 

7. Let's say he pulls over and looks at it. WOW! THAT BRAKE DISK IS RED HOT!!! SO'S THE CALIPER!! And yet, he can't SEE the expanded air and water vapor bubbles inside the caliper and brake line. By the time anything unusual is even noticed, the water vapor in the relatively cool brake line has already condensed back into liquid form and gone back into solution in the brake fluid.

 

8. Our hapless rider notices that the firmness has returned to his brake.

 

9. "Hey -- It's OK now! Last one to the bottom of the mountain buys the first round!"

10. Cue dramatic music and sirens, roll ambulance, paramedic team and tow truck with extra-long winch cable, and (potentially) call the coroner.

 

EDITORIAL NOTE: No animals were harmed in the above scenario. No bumps on mountain roads, no matter how horrific, caused the tiniest fraction of 32 G's of downforce on any brake levers as a cause of heat/drag cycles, though such G's -- and more -- may well have occurred to various parts of both machine and rider somewhere along the way to their final resting place(s) at the bottom of cliffs, (R.I.P.)

[Dan M]

 

1. air in the brake fluid

2. water in the brake fluid

3. an accumulation of brake dust/road grunge betwixt brake piston and caliper

 

 

In reference to the big 3, the culprit, I'd guess by a considerable margin is #3. Not only grunge around the piston but also at the edges of the pads where they ride in the caliper. These pads are a tight fit in the caliper, They are positioned low and have a cap over them helping brake dust and other contaminants collect. They have a noted history of binding (the famous rear brake groan).

Water contamination may play a roll if the reservoir is over filled. If the rider is checking / filling the fluid (for it to be overfilled to begin with) he's probably eliminating the water anyway. Enough water in brake fluid to allow boiling makes for some very dark fluid. I'd hope he would notice and not just fill it to the brim. In any case if it does get to this point, he will notice a spongy pedal before anything else happens. Has anyone with this catastrophic failure reported this loss of brake action before the lock up? And if there is vapor in the system, it will be at the hot spot (the caliper) so there will be no or low hydraulic pressure against the pads. This may cause overheated brakes but not likely a complete lock up.

[Guest ratchethack]

Has anyone with this catastrophic failure reported this loss of brake action before the lock up?

Yes. Per previous posts, the afflicted rider I wintessed with the complete brake seizure on the road reported entire loss of rear brake feel repeatedly moments before what he interpreted as "engine trouble" -- whereby lower gears and progressively more throttle were required to keep up with the group we were riding with. His idea was to "ride it out" by downshifting and wicking it up. He said he noticed that his disk was glowing red in the shadow of trees where he was literally forced off the road (under some considerable stress and very near loss of control) with a locked rear wheel. I missed that part, but by the time I stopped and parked, got to him and looked, the disk was more'n likely still hot enough to cook breakfast on. It had already cooled down to assume a brilliant multi-colored surface patina. I figured the disk was toast, but he's been riding on it for years since then and claims it's "just fine".

 

BTW -- one additional symptom was that his brake lever had dropped straight down with no ability to rest at it's stop. The only explanation for this I can think of is that boiling brake fluid stopped boiling when he was forced off the road. This must have allowed the brake fluid to cool rapidly, creating a vacuum in the line with the relief port closed.. The vacuum must have been strong enough to draw the master cylinder piston up in its bore against return spring pressure. I'm here to tell you it was not the kind of thing you'd EVER want to have happen on the road at any time. . . Gave me an abiding respect f'er the Big 3 on the spot, since his brake had been sorely neglected on all 3 counts. Him too.

And if there is vapor in the system, it will be at the hot spot (the caliper) so there will be no or low hydraulic pressure against the pads. This may cause overheated brakes but not likely a complete lock up.

May I suggest by personal witness -- Less than likely, but absolutely possible.

[dlaing]

What a load of nonsense on both sides.

 

Can't you and Ratch find something worth fighting over. It's like watching Tom and Jerry.

We'd fight over you, but you are not our type.

And by the way, what is wrong with Tom and Jerry? <_>

[dlaing]

The correct order, in order of most likely to cause brakes overheating, IMHO is

1. an accumulation of brake dust/road grunge betwixt brake piston and caliper.

2. failure for master piston to return due any of the following: foot resting on lever, restrictive dust boot, corroded rod, grunged seal, 1 Kg brake lever, sub zero clearance, brake lever stuck on exhaust pipe, etc. edit here is an example http://www.v11lemans.com/forums/index.php?...;hl=brake+groan

3. water in the brake fluid

4. air in the brake fluid

5. piss in the brake fluid

5. brake line resting on or very near exhaust.

6. Caliper falling off edit here is an example http://www.guzzitech.com/V11S-BrakeLosspic-Patrick.html

7. edit Not sure about this one, but I imagine wheel bearing failure could cause brake problems.

Here is a thread about that possibility http://www.v11lemans.com/forums/index.php?...=1162&st=15

 

BFG's problem was almost surely caused by #2, from the first bodge reducing freeplay to less than zero. As mentioned in post 36, with photographic EVIDENCE.

[Guest ratchethack]

BFG's problem was almost surely caused by #2, from the first bodge reducing freeplay to less than zero. As mentioned in post 36, with photographic EVIDENCE.

Uh oh. There's that pesky term, "evidence" being used incorrectly again, Dave.

 

The only EVIDENCE provided in the photo is that BFG's brake lever is wrapped up and apparently resting either against, or very nearly against its stop, with wot looks to be an allen key as a "splint". Not only does the photo not indicate in any way possible that free play is less than zero, but no such photo could EVER indicate that free play is less than zero. Further, the photo does not and cannot indicate, let alone be considered anything close to EVIDENCE of the cause of BFG's problem -- regardless of if "the problem" occurred either before or after the breaking and bodgery of the lever.

NOTE: For the more sensitive types who find this post or any other post offensive in terms of content, tone, or in any other way -- please take your complaint to the moderators. Much of what I find offensive on open Forums I'm able to ignore quite successfully without the effort of posting complaints as if I believe that what offends me offends everyone. This might be another option.

[docc]

NOTE: For the more sensitive types who find this post or any other post offensive in terms of content, tone, or in any other way -- please take your complaint to the moderators. Much of what I find offensive on open Forums I'm able to ignore quite successfully without the effort of posting complaints as if I believe that what offends me offends everyone. This might be another option.

 

This is an important and interesting topic. Unmaintained rear brakes, resting the foot on the brake, or building a heavy brake pedal all seem to be extraordinarily bad ideas. FWIW I bled my rear on the Sport every one to three years and only this last time took it off the bike and rotated the bleeder to the top. I was really pleasantly surprised at all the air that came out.

Definately this is the right way to do it along with the more frequent service interval.

 

Of course, the pedals do brake easily if the bike tips to the right. I rode mine home from its mishap with the front brakes only.

 

NOTE: The moderator has left the building.

[Dan M]

Yes. Per previous posts, the afflicted rider I wintessed with the complete brake seizure on the road reported entire loss of rear brake feel repeatedly moments before what he interpreted as "engine trouble" -- whereby lower gears and progressively more throttle were required to keep up with the group we were riding with. His idea was to "ride it out" by downshifting and wicking it up. <_ he said noticed that his disk was glowing red in the shadow of trees where literally forced off road some considerable stress and very near loss control with a locked rear wheel. i missed part but by time stopped parked got to him looked more likely still hot enough cook breakfast on. src="%7B___base_url___%7D/uploads/emoticons/default_wacko.png" alt=":wacko:"> It had already cooled down to assume a brilliant multi-colored surface patina. I figured the disk was toast, but he's been riding on it for years since then and claims it's "just fine".

 

If the brake was locking up for what ever reason. 1,2 or 3, there would be no effect pressing the pedal because the brake is already applied. The question, is did the pedal fade (become spongy) or was it just not responding since it was already applied?

 

 

BTW -- one additional symptom was that his brake lever had dropped straight down with no ability to rest at it's stop. The only explanation for this I can think of is that boiling brake fluid stopped boiling when he was forced off the road. This must have allowed the brake fluid to cool rapidly, creating a vacuum in the line with the relief port closed.. The vacuum must have been strong enough to draw the master cylinder piston up in its bore against return spring pressure. I'm here to tell you it was not the kind of thing you'd EVER want to have happen on the road at any time. . . Gave me an abiding respect f'er the Big 3 on the spot, since his brake had been sorely neglected on all 3 counts. Him too.

 

 

This makes no sense to me. Rapid cooling? Most of the fluid is in the caliper, I'd think it would stay hot for awhile, that is a bit of metal to cool down. Vacuum sucking the pedal down overcoming the master's internal spring? That's some vacuum. Why again is the relief port closed? Pedal must be depressed or insufficient freeplay in the linkagefor the master's piston to cover the port. If his brake was sorely neglected, how did it become overfilled? As the pads wear and the caliper pistons move out the fluid drops in the reservoir.

 

May I suggest by personal witness -- Less than likely, but absolutely possible.

[belfastguzzi]

Hey, I never suspected that this could be The New What Time Is It? thread!

 

The correct order, in order of most likely to cause brakes overheating, IMHO is

1. an accumulation of brake dust/road grunge betwixt brake piston and caliper.

2. failure for master piston to return due any of the following: foot resting on lever, restrictive dust boot, corroded rod, grunged seal, 1 Kg brake lever, sub zero clearance, brake lever stuck on exhaust pipe, etc.

3. water in the brake fluid

4. air in the brake fluid

5. piss in the brake fluid

5. brake line resting on or very near exhaust.

 

You left out

6. exploding fuel tank

and

7. Global Warming

 

...building a heavy brake pedal all seem to be extraordinarily bad ideas.

I did NOT build a heavy brake lever!

 

I can see that I'm going to have to weigh the thing at some stage

[dlaing]

Uh oh. There's that pesky term, "evidence" being used incorrectly again, Dave.

 

The only EVIDENCE provided in the photo is that BFG's brake lever is wrapped up and apparently resting either against, or very nearly against its stop. Not only does the photo not indicate in any way possible that free play is less than zero, but it cannot indicate that free play is less than zero. Further, the photo does not and cannot indicate, let alone be considered anything close to EVIDENCE of the cause of BFG's problem.

 

NOTE: For the more sensitive types who find this post or any other post offensive in terms of content, tone, or in any other way -- please take your complaint to the moderators. Much of what I find offensive on open Forums I'm able to ignore quite successfully without the effort of posting complaints as if I believe that what offends me offends everyone. This might be another option.

 

NOTE: The moderator has left the building.

docc, thanks for taking your complaint to us rather than back stabbing us with anonymous complaints to jimbemotumbo, who has not posted since October.

I really wanted to argue with Ratchet about the dangerous cause of BFG's mishap, that could occur again from a careless bodge job, but to make you, Nogbad, and others happy, I am done with this thread.