Boiling Fluid

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Just wondering if anyone else has experienced boiling rear brake fluid. I have a 98 non ABS pan with 55000 miles on the clock. Whilst descending the Stelvio Pass in Italy this summer the rear pedal became soft and then all resistance was lost very quickly, fronts stayed fine. The fluid was changed about two years ago but i will now obviously do it again. For those that don't know the Stelvio is one of them must ride roads, 1000's of feet up and down and too many hairpins to count. I was having to cover the rear brake because the gradient doesn't slow down any on the bends and with being two up with luggage it would have run away with itself. I wouldn't say I was pushing that hard but riding with a little gusto. I predict the issue was a fully loaded bike, high ambient, type of road and what amounts to a pretty much enclosed rear brake system when everything is behind plastic. I would appreciate your views. If you would like to view the bike on the pass visit......photo Stelvio on the interweb for the 01 07 16 between 1600-1630 and on page 4. Thanks
.:confused:
The brake returned to "normal" after about 10 minutes non use, just using the front.
 
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Thanks for the heads up on the origin of the name for the Moto Guzzi Stelvio.

I've never experienced your problem, but I would check all the basics first. Does the rear brake drag with the bike on the center stand? Since the front brakes absorb most of the energy when braking, I would wonder about the secondary master cylinder (not all that familiar with the 1100 - so this is a guess) working properly. Might you be doing most of your braking with the rear? This could indicate a weak front brake.
 
OP
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Thanks for the heads up on the origin of the name for the Moto Guzzi Stelvio.

I've never experienced your problem, but I would check all the basics first. Does the rear brake drag with the bike on the center stand? Since the front brakes absorb most of the energy when braking, I would wonder about the secondary master cylinder (not all that familiar with the 1100 - so this is a guess) working properly. Might you be doing most of your braking with the rear? This could indicate a weak front brake.
Yes I was covering the rear brake an awful lot, 500 kg downhill around hairpins, it had to be done....but the brake is in good order the caliper recently serviced and not dragging and pads in good order. Rear disc also renewed about 5000 miles ago with genuine part. It's a mystery. A fairly scary one at the time. I didn't tell her indoors until we reached the bottom and the brake was back with me. But I was braking probably 80-20 front rear bias approaching the bends, so fairly easy on the rear one.
 
OP
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If you're boiling brake fluid in the rear or front you're in the wrong gear. Downshift!
I don't disagree with your reasoning, it's a tried and tested formula, but the Stelvio and other Alpine passes are not your average Interstate. Before you shout at me that the good old USA has bends too, yes I know; I've travelled through some of your mountain areas in the West, about 10000 ft if I remember right. But the roads are a different riding prospect and first would have been way too low but second just a little high. First would have been difficult as well because the ambient temp was very high 30 plus at 8000 ft, sorry 85f and you don't want an overheating motorcycle 1500 miles from home.
But the question was has anybody else experienced the issue and if so, WHY? As I said I wasn't riding too hard, just enjoying the ride.
 
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On my travels out west every year I see someone at the bottom of a steep descent with smoke pouring from their wheels (cars) tires actually on fire (SUVS or pickups pulling trailers) and even occasionally a rookie semi driver "rolling smoke"....all used the wrong gear for their descent. Engine braking saves the brakes from overheating...they aren't meant to be used ten miles continuously at a time, they overheat and cook everything....2 cents, envy the riding of the Stelvio and other options you have....ride safe........ff
 

ST1100Y

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...The fluid was changed about two years ago...
Well, this is one clue... 2 yeas in the humid climate of the Brit Isles... hmm...
The second would be what brand/type of brake fluid was used... regular automotive or motorcycle racing type...

Riding ST1100's since '92 I always used exclusively BelRay Super DOT4 brake fluid; never had an issue... ever... and I'm an ambitious rider, with much/hard use of the rear brake for trailing in tight corners...
Only once, in '03 I had exactly the same symptoms/fail of the rear brake as described on the S?lkpass here in AuSTria... 2-up with luggage quite a pucker moment streaming towards a tight hairpin and finding the brake pedal falling through with no resistance... managed to decelerate with the front only (painful on the tions), and to pump the rear brake back up after making the turn, to be ready for the next, just 30 meters later...

Causes?
For whatever reason the system was filled with budget Castrol brake fluid... yuch...
Got home, flushed the Castrol sludge out with my well trusted BelRay, never had a problem again.
One can argue higher costs back and forth, but having the boiling point some degrees above "normal" specs does pay off at times... especially in the Alps up here...
 

CYYJ

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The only guess I can make as to the cause of the 'boiling fluid' is that the fluid in your system did not meet specifications. Although it might have been 'DOT 4' fluid (assuming that's what the spec is), it is possible that it was a bad batch, or that the original container had been open and exposed to atmosphere for some time. It is also possible that when the fluid was last changed, the new fluid added was perfectly good, but the system was not thoroughly flushed to get rid of all the old fluid, and as a result, some moisture remained.

My guess is that the brake fluid itself did not boil, what boiled was moisture in the brake system.

I keep my ST 1100 in Switzerland, and last rode the Stelvio 18 days ago (not a hot day, I grant you), but I did ride the pass hard... I then rode through numerous passes in France before going through the Pyrenees from east to west. My ST 1100 has 175,000 km on it, and I have never had a problem with brakes.

Michael
 
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(painful on the tions)
took me a minute to decode this, first I thought it was a typo, then it clicked. The word you want is "shins". The way you spelled it would be pronounced the same way when its at the end of a word, but its never used as a standalone word.
 

ST1100Y

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The word you want is "shins".
Actually no (kept feet well on the pegs there):
The connective tissue (ligaments) on the inside of your wrist, used to bend your fingers/close fist via muscles in the forearm, in particular index- and middle finger used to clamp on the front brake to compensate the sudden, unexpected loss of aprox 40% braking capacity due to failure of rear brake hydraulics ;-)

I should get a medical dictionary as well, trying to search translation of medical terms online is total BS... :)
 
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Actually no (kept feet well on the pegs there):
The connective tissue (ligaments) on the inside of your wrist, used to bend your fingers/close fist via muscles in the forearm, in particular index- and middle finger used to clamp on the front brake to compensate the sudden, unexpected loss of aprox 40% braking capacity due to failure of rear brake hydraulics ;-)

I should get a medical dictionary as well, trying to search translation of medical terms online is total BS... :)
"Tendons" ??
 

ST Gui

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The connective tissue (ligaments) on the inside of your wrist, used to bend your fingers/close fist via muscles in the forearm
And occasionally damaging a tendon in a finger or two aka 'trigger finger' (stenosing tenosynovitis). Typically it requires some repetition along with significant gripping force but that's all variable.
 
OP
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Thanks for the heads up on Bel Ray, I will definitely give it a whirl. I can't honestly say what brand is currently in but most probably Motul. I also agree with the comment re water content and this boiling water being the culprit, although difficult to be 100 percent. Bel Ray is available in England and is roughly the same price as the rest. Ta fellow bikey muckers.
 

bdalameda

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If your brake fluid is old and has absorbed moisture this type of brake failure can happen when the moisture vaporizes with heat. I have seen it quite a few times especially riding with friends in the mountains with a lot of downhill braking. Usually a fluid change will help a lot along with being conservative with the rear brakes.

Dan
 
OP
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Does the ST1100W have the combined braking system ?

Certainly the old fluid would not help, it absorbs moisture over time and 2 years is the absolute limit for flushing out the system with new. I have seen mine go off (it becomes cloudy) in just over 12 months. I live in Yorkshire, and Northumberland can be much wetter.

I've been down the mountain passes in Austria, Alps and in Spain with an 1100 and the 1300 and I have never had this.

The only times I got a very hot back brake was due to:
i - problems with the front brake pads (new ones slightly too thick) dragging slightly enough to operate the combined braking via the SMC
ii - problems with the rear calliper not releasing the pads from the disc surface - this was self inflicted by over-greasing the slider pins. The accumulated air pressure, unable to escape, pushed the pads against the disc.
But if the pads release in between application of the brakes, they should not overheat to that extent.

Have you got the white heat pads on the disc pads ? They are there to prevent the heat from the discs transferring to the calliper.
But you don't need them in the front - if you put them there, you get the problem # i that I mentioned.
Thanks John, it is not a linked system and the brake releases fine and all the bits are there. It was all thoroughly overhauled only two years ago and only sees rain on longer journeys. I do think the fluid is the culprit and am wondering if it was linked would I have lost both brakes?
I was unfortunate enough a long time ago when riding a ST1100 and the front caliper retaining pin unscrewed itself allowing the caliper to swing out and hit the wheel. This resulted in thankfully temporary total brake failure until I was able to pump the levers frantically to regain some brake effort. Very unpleasant pants soiling moment. Before you ask, no I didn't put the brake back together, it was a works bike and the mechanic was sacked as a result. Harsh but the consequences could have been a lot worse than dirty underwear. Once again thanks for your input although I obviously dispute your views on Northumberland weather, now where are my waterproofs.
 

lomita

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What type brake pads do you have, sintered, ceramic, etc.?

A synthetic brake fluid will combat overheating. Fade on brakes, check pads and rotors. If glazed, replace. That's my 2 cents. After switching to a synthetic, never had an overheat of fluid again. I'm a believer in stainless steel brake lines too. Good luck.
 
OP
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What type brake pads do you have, sintered, ceramic, etc.?

A synthetic brake fluid will combat overheating. Fade on brakes, check pads and rotors. If glazed, replace. That's my 2 cents. After switching to a synthetic, never had an overheat of fluid again. I'm a believer in stainless steel brake lines too. Good luck.
They are Honda pads, about two years old and in good nick. Yes I will change fluid as per previous post. I think the fluid recommended was Bel Ray or similar and I can source it in the UK. Thanks for help.
 
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Change your brake fluid to the 5.1 , this is having a higher boiling punt than the 4.0 version.
Changes every two years the fluid or, if you do a lot of miles a year , changes it every year .
Its not much work .
that`s my 2 cents for a save riding.
 
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Change your brake fluid to the 5.1 , this is having a higher boiling punt than the 4.0 version.
just make sure its DOT5.1 (glycol based, compatible with DOT4) and not DOT5 (silicone based, not compatible with DOT4)
 
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just make sure its DOT5.1 (glycol based, compatible with DOT4) and not DOT5 (silicone based, not compatible with DOT4)
Just in motion of reading all threads on breaks for st1100 & here is my input for what it’s worth... I’ve been using bosh brake fluid ESI6 extended service DOT 3,4 & 5.1 compatible in all my things with breaks... (I wish I could access the military spec “5” as it contains silicone and will not absorb moisture! Yes I understand you would have to do a complete flush maybe even a line change but it’s better better better!)

That being said I am about to attack the ABS system on my 2001 and do a complete flush with the Bosch brake fluid ESI # 6.

So my long winded question is,
has anybody used the Bosch with negative results?
 
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