Linked brakes not so bad
- Thread starter RBEmerson
- Start date
Help Support Yamaha FJR Motorcycle Forum:
Lets be clear about this. The only brakes that are hydraulically linked are the (single) normal rear caliper and one of the four front caliper pairs.
The ABS has three separate circuits. One circuit goes to the front three piston pairs operated by the front lever. The second circuit goes to the rear caliper. The third circuit affects only the linked fluid line, going from the rear master cylinder to the linked front piston pair.
If the rear brake fluid boils it creates vapor (not air) in the hydraulic line. The rear and linked brakes would both fade, but the front 3 pairs will be unaffected. Likewise, if the front fluid boils, the front brakes would fade but the rear and linked front brake would be unaffected.
The ABS doesnt sense anything except wheel rotation speed. It would not magically release front brake pressure unless the front wheel rotates too slowly, which is what its designed to do when the wheel locks up.
Also, FWIW, as soon as the brakes cool the vapor recondenses and braking would return to normal.
One more point: It is unusual that the rear brake was bound up enough to boil the brake fluid unless... that brake fluid was also very old, which is quite possible on a bike that hadnt had the brake lever pivot greased.
DOT4 brake fluid, which is what is called for on your FJR, doesnt boil until it reaches over 445 degrees F. when new. Old brake fluid boils at a lower temperature because the glycol-ether fluid absorbs water out of air (humidity). As the percentage of water increases, the boiling point goes down, (toward the 212 F boiling point of the water).
The ABS has three separate circuits. One circuit goes to the front three piston pairs operated by the front lever. The second circuit goes to the rear caliper. The third circuit affects only the linked fluid line, going from the rear master cylinder to the linked front piston pair.
If the rear brake fluid boils it creates vapor (not air) in the hydraulic line. The rear and linked brakes would both fade, but the front 3 pairs will be unaffected. Likewise, if the front fluid boils, the front brakes would fade but the rear and linked front brake would be unaffected.
The ABS doesnt sense anything except wheel rotation speed. It would not magically release front brake pressure unless the front wheel rotates too slowly, which is what its designed to do when the wheel locks up.
Also, FWIW, as soon as the brakes cool the vapor recondenses and braking would return to normal.
One more point: It is unusual that the rear brake was bound up enough to boil the brake fluid unless... that brake fluid was also very old, which is quite possible on a bike that hadnt had the brake lever pivot greased.
DOT4 brake fluid, which is what is called for on your FJR, doesnt boil until it reaches over 445 degrees F. when new. Old brake fluid boils at a lower temperature because the glycol-ether fluid absorbs water out of air (humidity). As the percentage of water increases, the boiling point goes down, (toward the 212 F boiling point of the water).
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lnewlf
Well-known member
and there you have it folks as concise as possible....the hoss is now dead..
One flicker of life... Vapor or air (agreed - only if lines or connections are compromised), there's still something in there that's compressible, no.? Given everything else has pretty much turned to c***, it's a small point. But raised purely for sake of nailing down one last loose thread of comprehension on my part.
Yes. Air or vapor in the lines is compressible. When the bubble is larger than the amount of fluid displaced by the master cylinder you will have no braking.
The difference is that vapor goes away after it cools. Air does not. None of this is any different than in any other hydraulic brake system.
The difference is that vapor goes away after it cools. Air does not. None of this is any different than in any other hydraulic brake system.
rbentnail
Economic Plankton
Wait. What? You still haven't RTFM? And now magically everything's ok? Geez..... why are you posting?TNX - I'm honestly happy to hear that.
plus you won't be getting bent over on the forum..
More than anything, it's probably a function of praising or panning something without actually using it first. Sort of like CNN and reporting on something without any actual information about it. In the earlier days of the forum there was a guy who claimed how fast he could run through the gears based on sitting on the bike in the garage with the motor off.
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Sounds good to me.
Too bad some a****** are legends in their own minds and don't get trying to understand the details.
Understanding the details can be a good thing unless it becomes obsessive and gets in the way of actions/decisions. That's called analysis paralysis and is a real thing. The deal of knowing something is bad or good without giving it a chance to see how it works is something different.
No OCD, just interest in what I'm betting my hide on. Devil's in the details.
Gurock
Well-known member
I was busy picking up my new to me 09 FJR AE. Ive never understood why I lost both the front and back brakes at the same time that day. The only things I know for sure is
1. Fred is right its the pivot not the splines. That proves why Ill never be a mechanic.
2. The rear brake was stuck on at freeway speed long enough to cook something.
3. That when the brakes fails I could pull front or push rear with no effect at all.
4. I tried pumping as it was failing to have effect without effect.
5. When I was able to stop by engine brake and running out of momentum, I turned off the bike, put in nutural, and thank god I was ok.
6. Five or ten minutes later I started the engine, pumped the brakes for a minute or so and tested the brakes safely. The brakes worked as well as ever..
I took a twenty minute break, had some coffee, worked up my courage and rode on without incident for seven hundred more miles that day.
Im a fool for a mechanic and maybe the story makes me a greater fool, but thats what happened.
1. Fred is right its the pivot not the splines. That proves why Ill never be a mechanic.
2. The rear brake was stuck on at freeway speed long enough to cook something.
3. That when the brakes fails I could pull front or push rear with no effect at all.
4. I tried pumping as it was failing to have effect without effect.
5. When I was able to stop by engine brake and running out of momentum, I turned off the bike, put in nutural, and thank god I was ok.
6. Five or ten minutes later I started the engine, pumped the brakes for a minute or so and tested the brakes safely. The brakes worked as well as ever..
I took a twenty minute break, had some coffee, worked up my courage and rode on without incident for seven hundred more miles that day.
Im a fool for a mechanic and maybe the story makes me a greater fool, but thats what happened.
Redfish Hunter
Gone Fishing
Something Different?
I am still trying to figure out if this guy is for real, a troll, or just a shit stirrer. My grouchy friend the bent nail guy does have a point. These lively and entertaining discussions could probably not have occurred had the OP simply RTFM.
I thought I was pretty familiar with the FJR platform when I bought my '15ES. I had been maintaining Dad's FJR for 8 years and had been a member of this forum for quite a few years. Yet I felt compelled to read and re-read the owner's manual the first night I had it. I still go back and consult that manual. Amazing how much information Yamaha put in that thing.
This is a Kinder and Gentler Forum these days. We are doing our best to embrace newb/noob questions. I hope we are doing The Right Thing.
Out of curiosity, did you need to pump the brakes (line 6), or did that just seem like the thing to do?
Have you had the brake fluid changed? Did you or the dealer add fluid?
BTDT with a failure (not FJR) in rural NC and a need to get home. I opted for interstates over back roads, thinking that, aside from a sudden stop / crash ahead, stopping was only needed at gas stops, and, with planning, I could get enough braking to stop at a pump. Not a pleasant ride.
Have you had the brake fluid changed? Did you or the dealer add fluid?
BTDT with a failure (not FJR) in rural NC and a need to get home. I opted for interstates over back roads, thinking that, aside from a sudden stop / crash ahead, stopping was only needed at gas stops, and, with planning, I could get enough braking to stop at a pump. Not a pleasant ride.
FWIIW, I found the OM on line and went through it before pulling the trigger. NTL sometimes practical experience wins out over hyper-sensitive liability-adverse manuals. And sometimes manuals get it wrong (gasp!!). The only brake diagram I found was on 1-11 of the shop manual, not in the on-line OM (I'm too lazy to go to the garage to get the hard copy).
The experience of losing front and rear brakes at the same time raises the question of whether or not the ABS ECU had a brain burp. If so, if it did it once, unless it was checked out, it might do it again. Or maybe the metering valve didn't like what happened when the rear brake "cooked"?
@Gurock: Why did the rear brake stick? How stuck is "stuck"? The "fix" was to let everything cool down, right?
The experience of losing front and rear brakes at the same time raises the question of whether or not the ABS ECU had a brain burp. If so, if it did it once, unless it was checked out, it might do it again. Or maybe the metering valve didn't like what happened when the rear brake "cooked"?
@Gurock: Why did the rear brake stick? How stuck is "stuck"? The "fix" was to let everything cool down, right?
RossKean
Well-known member
I suppose that it is possible (although unlikely) that a very badly stuck rear brake could cook the fluid in the rear brake and a stuck linked front piston could overheat the whole front caliper (and the front brake circuit) rendering the front inoperative as well. This would have to be VERY bad for a period of time and the hydraulic fluid would have to be pretty wet. Can't imagine riding with the resultant poor throttle response, not to mention the stench of roasting brake pads.
The ABS ECU having a brain burp when the rear brake cooks the fluid (whatever that really was) is probably reaching for it. If 1-11 is correct, the only other point of contact between the two circuits is the metering valve. Vapor develops in the rear brake line (agreed that's reaching for it), causes the metering valve to do something weird, and the front brakes respond to whatever weird thing the valve does. Still a string of coincidences, though. But then, so's the rear brake acts up and the front brake does, too. [/ head scratch ]
Gurock
Well-known member
I dont mean to make trouble for anyone. The particular FJR that did it was one of about five that ive Owned in the last ten or so years. I have many years and miles on FJRs. I do know that later on with the rear wheel off the pads appeared to be missing chunks of pad and I had them changed.
I also knew that the rear brakes had a habit of sticking a little. Its what Fred said the pedal would stick. Id been used to using my boot to make sure the pedal didnt end up stuck but must not have right before I turned onto the I 55 ramp near Litchfield, IL and when I got off the I 270 in Missouri the brakes barely worked at the top of the ramp. 2 blocks down at the next red light, no brakes.
Answering the other question I dont know that pumping did any good. It just seemed like the thing to do. The brake fluid had not been recently changed or the brakes worked on in any way. Also there was no ram mount or such attached to the master cylinder.
I just plain admit to mechanical ignorance. Im a lawyer by trade. Since this happened only once to me and never again, I just wrote it off as an awful scare with a happy ending.
Ive enjoyed being on this forum for years and wouldnt want to ruffle anyones feathers or get any one mad. If Ive done so Id like to say sorry.
I also knew that the rear brakes had a habit of sticking a little. Its what Fred said the pedal would stick. Id been used to using my boot to make sure the pedal didnt end up stuck but must not have right before I turned onto the I 55 ramp near Litchfield, IL and when I got off the I 270 in Missouri the brakes barely worked at the top of the ramp. 2 blocks down at the next red light, no brakes.
Answering the other question I dont know that pumping did any good. It just seemed like the thing to do. The brake fluid had not been recently changed or the brakes worked on in any way. Also there was no ram mount or such attached to the master cylinder.
I just plain admit to mechanical ignorance. Im a lawyer by trade. Since this happened only once to me and never again, I just wrote it off as an awful scare with a happy ending.
Ive enjoyed being on this forum for years and wouldnt want to ruffle anyones feathers or get any one mad. If Ive done so Id like to say sorry.
@Gurock - I dont think youre making trouble for anyone. We are just trying to understand what happened to you. The idea that the rear brake overheating caused the front brake to fade is hard one to understand.
Is it possible that you are (or were) primarily a rear brake user? That when the rear brake faded you panicked and did not use the front brake? Or was the front lever soft as well? Could you feel pulsation in either the rear pedal or front lever that would suggest the ABS was activated?
FWIW - The metering valve (as well as the proportioning valve) is in the linked hydraulic circuit. It only affects the lower front right piston pair.
@Ross , I dont think a sticking rear brake pedal would create enough fluid pressure to get past the metering valve, never mind overheat the front rotor.
Is it possible that you are (or were) primarily a rear brake user? That when the rear brake faded you panicked and did not use the front brake? Or was the front lever soft as well? Could you feel pulsation in either the rear pedal or front lever that would suggest the ABS was activated?
FWIW - The metering valve (as well as the proportioning valve) is in the linked hydraulic circuit. It only affects the lower front right piston pair.
@Ross , I dont think a sticking rear brake pedal would create enough fluid pressure to get past the metering valve, never mind overheat the front rotor.
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RossKean
Well-known member
Yah, I don't think so either but unless that piston pair was also activated (a lot), I can't understand how the front could have been affected. If that caused the whole front caliper to cook, it is just barely possible.
rbentnail
Economic Plankton
You have no idea the response I was typing when I said, "Dood! You sound like Denis Leary! Stop it!!" Thank you for noticing the kinder, gentler me.Something Different?
I am still trying to figure out if this guy is for real, a troll, or just a shit stirrer. My grouchy friend the bent nail guy does have a point. These lively and entertaining discussions could probably not have occurred had the OP simply RTFM.
I thought I was pretty familiar with the FJR platform when I bought my '15ES. I had been maintaining Dad's FJR for 8 years and had been a member of this forum for quite a few years. Yet I felt compelled to read and re-read the owner's manual the first night I had it. I still go back and consult that manual. Amazing how much information Yamaha put in that thing.
This is a Kinder and Gentler Forum these days. We are doing our best to embrace newb/noob questions. I hope we are doing The Right Thing.
And thus the paralysis begins. RBE if you're scared of brakes, here's a suggestion: simply don't use them. Problem solved, send beer.
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