For a couple of years now, my rear brake works fine while I'm riding until I ride really aggressive for more than a few minutes. Then it just disappears for the rest of the ride. By the time I get it back to the garage to examine it, it's working fine again. I have bled it. I have flush replaced the fluid in it. It is not leaking. The pads and disc are in good shape. My best guess is that I'm boiling the fluid? I would think that would cool down relatively quickly and start working again in a few minutes. Not the case.
WTH?
Rear brake question
This is much like the overheating of the engine issues..
You have the "cause".... and you have the "symptom".
You can treat either one...
The cause is excessive heat being created by the rear brake is boiling the fluid. This can be caused my either mechanical issues, or simply by using the rear brake lever as a foot rest ( as I usually do!)
Mechanical Issues are:
Too thin of a rotor.
Piston semi -frozen in the caliper.
Caliper semi frozen in the mount.
All these are easy to investigate...
Useing the lever as a foot rest is corrected by adjusting the pedal height or simply ride standing up more.
Another way to deal with the issue is using the equivalent of " Evans Coolant" for the brakes....
http://www.wilwood.com/Products/006-Mas ... /index.asp
EXP 600 PLUS SUPER HIGH-TEMP RACING BRAKE FLUID:
EXP 600 Plus is a highly refined blend developed for extreme performance under the high heat and extreme pressure of professional motorsports.
What’s in a number?
EXP 600 Plus has tested to 626 degrees F with a wet boiling point of 417 F. These numbers far exceed any DOT or SAE specifications.
What’s the real test?
It is true that racing fluids need to have high boiling points. It is also true that fluids need to have low moisture affinity to slow the natural absorption rate of water vapor. But the true test of any fluid is how well it resists aeration and compressibility after it has been heated and pressure cycled a few hundred times. The real test is at the track. EXP has proven to maintain firm pedal feel and quick response, long after others have failed.
Where’s the proof?
A Winston Cup car racing for 500 laps at Martinsville is the most grueling brake test in all of motorsports. The brakes will be applied up to 1,000 times, plus pit stops, at sustained high heat and repeated high pressure. IRL, CART, ASA, Busch, Craftsman Trucks, and a whole world of other oval and road course competition series also demand extreme performance from their brake systems. EXP 600 Plus has passed the test in every series!
Note:
For optimum performance, EXP 600 Plus should not be diluted with any other brake fluids. Add new fluid to a clean system.
Using this product will keep the fluid in the caliper from boiling, but it dosent address the condition that is creating the boiling.. get it?
Your pedal will be hard, but if the brake system is heat soaked... the brake effectiviness will be severly compromised.
Translation... The pedal will be hard, but no mater how hard you stomp on it.... the bike isnt going to stop..
Let me know if this help MoJo... I can go into greater detail if need be....
You have the "cause".... and you have the "symptom".
You can treat either one...
The cause is excessive heat being created by the rear brake is boiling the fluid. This can be caused my either mechanical issues, or simply by using the rear brake lever as a foot rest ( as I usually do!)
Mechanical Issues are:
Too thin of a rotor.
Piston semi -frozen in the caliper.
Caliper semi frozen in the mount.
All these are easy to investigate...
Useing the lever as a foot rest is corrected by adjusting the pedal height or simply ride standing up more.
Another way to deal with the issue is using the equivalent of " Evans Coolant" for the brakes....
http://www.wilwood.com/Products/006-Mas ... /index.asp
EXP 600 PLUS SUPER HIGH-TEMP RACING BRAKE FLUID:
EXP 600 Plus is a highly refined blend developed for extreme performance under the high heat and extreme pressure of professional motorsports.
What’s in a number?
EXP 600 Plus has tested to 626 degrees F with a wet boiling point of 417 F. These numbers far exceed any DOT or SAE specifications.
What’s the real test?
It is true that racing fluids need to have high boiling points. It is also true that fluids need to have low moisture affinity to slow the natural absorption rate of water vapor. But the true test of any fluid is how well it resists aeration and compressibility after it has been heated and pressure cycled a few hundred times. The real test is at the track. EXP has proven to maintain firm pedal feel and quick response, long after others have failed.
Where’s the proof?
A Winston Cup car racing for 500 laps at Martinsville is the most grueling brake test in all of motorsports. The brakes will be applied up to 1,000 times, plus pit stops, at sustained high heat and repeated high pressure. IRL, CART, ASA, Busch, Craftsman Trucks, and a whole world of other oval and road course competition series also demand extreme performance from their brake systems. EXP 600 Plus has passed the test in every series!
Note:
For optimum performance, EXP 600 Plus should not be diluted with any other brake fluids. Add new fluid to a clean system.
Using this product will keep the fluid in the caliper from boiling, but it dosent address the condition that is creating the boiling.. get it?
Your pedal will be hard, but if the brake system is heat soaked... the brake effectiviness will be severly compromised.
Translation... The pedal will be hard, but no mater how hard you stomp on it.... the bike isnt going to stop..
Let me know if this help MoJo... I can go into greater detail if need be....
Last edited by AlisoBob on June 28th, 2007, 5:14 pm, edited 1 time in total.
I burn up 3 sets of pads on the rear per season. Guess it has to do with an old school riding style a good bro and former open class champ has taught me. But, it works.
Only thing I can think of is you may need to look at the master cylinder in the back, if your runnin the good DOT 4 fluid.
BTW, on my last visit to Bennys, I noticed that he fitted an 80's Honda dual piston caliper to the rear of his KX500. The mount he made for it looks like factory stuff...... I'll shoot a pic of it this weekend. Think I may have to fire up the Cinnci and make a few for the CR's
Only thing I can think of is you may need to look at the master cylinder in the back, if your runnin the good DOT 4 fluid.
BTW, on my last visit to Bennys, I noticed that he fitted an 80's Honda dual piston caliper to the rear of his KX500. The mount he made for it looks like factory stuff...... I'll shoot a pic of it this weekend. Think I may have to fire up the Cinnci and make a few for the CR's
Kalkaska, the inbred capital of Michigan. ....a place you can walk into the greeting card aisle and find one that reads "Happy Birthday Uncle Dad"
If you do ever lose the rear brake out on the trail.... usually if you hose off the rear caliper with water, the vapor that is created by the boiling fluid recombines with the fluid and normal operation returns without any kind of bleeding or other fiddling around...
Make sure that BOTH the caliper and piston have cooled down. A cool capiler and hot piston could lead to more brake dragging issues. Give it a good 5 minutes or so.....
Make sure that BOTH the caliper and piston have cooled down. A cool capiler and hot piston could lead to more brake dragging issues. Give it a good 5 minutes or so.....
Bah! Brakes are for pussies!AlisoBob wrote:If you do ever lose the rear brake out on the trail.... usually if you hose off the rear caliper with water, the vapor that is created by the boiling fluid recombines with the fluid and normal operation returns without any kind of bleeding or other fiddling around...
Make sure that BOTH the caliper and piston have cooled down. A cool capiler and hot piston could lead to more brake dragging issues. Give it a good 5 minutes or so.....
So, is this a common problem for the rest of you? Speedburn...? You out there? I'm especially interested in your take as your riding seems quite similar.
I'm pretty conscious of what is going on with my rear brake. I'm not a brake dragger... until I get aggressive. Bombing through the tight stuff, my rear wheel is alternating between 25 mph and 0 in roughly 1-3 second intervals. This is intentional as I am typically using both ends of the bike to steer. Stuff the front wheel into the corner and swing the rear around and nail it coming out. My foot never leaves the pedal.
Pretty soon, the pedal goes soft. This should be a major clue, but I don't know what it means. Water in the fluid that I am vaporizing? Even an hour of riding casually, without hardly touching the rear brake, it doesn't recover. This only became a problem a couple of years ago, and I guarantee, I haven't become MORE aggressive.
For right now, my plan of action is:
1. Examine disc thickness.
2. Examine caliper operation.
3. Examine brake pads for glaze.
4. Drain all fluid and then replace with freshly opened bottle.
Sound about right?
A friend mentioned something about maybe the brake line is going bad and ballooning when it gets heated. That doesn't compute with me... Aging brake lines typically are going to fail digitally.
It sounds like the piston is somewhat frozen in the caliper... Age, heat, pressure washing chemicals, etc.. and all make this happen.
Get the Caliper overhaul kit:
06431-MA3-405 SEAL SET, PISTON $4.10
Double check the part number for your year.....
Disassemble the caliper, clean out all the gunk.. polish the piston bore with some #800 wet / dry sandpaper lubed with brake fluid.. Clean up and reassemble.
The piston should move vary easily if it is all good and well.
Also make sure that the caliper "floats" on the studs ,and isnt hung up in anyway. Correct as needed. If your pads are wearing more one one side than the other, YOU HAVE ISSUES!
If the piston or caliper are not free to move, the slight drag against the rotor, over prolonged periods of time, can build up allot of heat. Add the heat generated from your "stab" braking.. and that could add up to fluid boiling, and the loss of pedal that you are having.
The part of your description where you describe it as "not recovering " is consistent with mechanical brake drag issues...
Also , different pad types have different amounts of friction. I tried the EBC Sintered Metal pads, and like the results... From EBC.....
"These pads are an excellent choice of all weather performance formulation for moto-X and ATV racing, with the highest HH rated friction for maximum stopping power.
The latest American made sintered pads produced by EBC in their OWN FACTORY is the MXS series. These pads have the HIGHEST friction of any publicly available brake pad and deliver fingertip stopping power in moto-x race conditions. Being a sintered copper alloy they also have excellent durability in sand, wet and mud riding and are at the same time less aggressive to the brake rotor."
Check her out MoJo, you'll get her dialed in!
Get the Caliper overhaul kit:
06431-MA3-405 SEAL SET, PISTON $4.10
Double check the part number for your year.....
Disassemble the caliper, clean out all the gunk.. polish the piston bore with some #800 wet / dry sandpaper lubed with brake fluid.. Clean up and reassemble.
The piston should move vary easily if it is all good and well.
Also make sure that the caliper "floats" on the studs ,and isnt hung up in anyway. Correct as needed. If your pads are wearing more one one side than the other, YOU HAVE ISSUES!
If the piston or caliper are not free to move, the slight drag against the rotor, over prolonged periods of time, can build up allot of heat. Add the heat generated from your "stab" braking.. and that could add up to fluid boiling, and the loss of pedal that you are having.
The part of your description where you describe it as "not recovering " is consistent with mechanical brake drag issues...
Also , different pad types have different amounts of friction. I tried the EBC Sintered Metal pads, and like the results... From EBC.....
"These pads are an excellent choice of all weather performance formulation for moto-X and ATV racing, with the highest HH rated friction for maximum stopping power.
The latest American made sintered pads produced by EBC in their OWN FACTORY is the MXS series. These pads have the HIGHEST friction of any publicly available brake pad and deliver fingertip stopping power in moto-x race conditions. Being a sintered copper alloy they also have excellent durability in sand, wet and mud riding and are at the same time less aggressive to the brake rotor."
Check her out MoJo, you'll get her dialed in!
Yeah I hear you I don't know how much it helps but it's made by Devol and is supposed to help keep the fluid cooler. They make couple different coolers.AlisoBob wrote:For the heat to leave the caliper, travel up the swing arm, through the long hose and into the master cylinder, and then pass the heat off into the airstream via a finned cover is a bit of a stretch in my opinion..
http://www.devolracing.com/home.htm
I saw a photo of a little finned goodie that DeVol is making that mounts to the caliper, that the brake line mounts to.
Its a far better idea, than the master cylinder mounted one...
I still question its effectivness though... Your relying on the heat being conducted through a static medium ( The Fluid).
I dont see it.
Its a far better idea, than the master cylinder mounted one...
I still question its effectivness though... Your relying on the heat being conducted through a static medium ( The Fluid).
I dont see it.
