KX450F rear brake overheats badly...what to change...

user760a
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9/14/2015 7:39pm Edited Date/Time 9/15/2015 6:35pm
I really dont drag the brake too much, but I do use it to kind of stabilize the bike through a lot of corners. It gets extremely hot and at that point,. even the lightest application of rear brake results in a chirp and lock situation. It is impossible to modulate the brake when it is that hot: its either no brake or chirp and lock the wheel. This is the story on a MX track- the other day in a two hour hare scramble with six laps of a nine mile course that has about 350 turns a lap (so it seems) I did not even make it through one lap before the brake was so hot it was all or nothing. It is impossible to flow when your rear brake is constantly locking

I have lowered the pedal (a lot) to avoid unintended brake drag. Have changed the brake fluid (just replaced with the standard dot 5) , and have even ground two quarter inch vertical grooves in my pads to aid cooling and lower friction a bit..all to no avail

has anyone had this problem? any tips? I am wondering if lower friction pads, extra insulators, a different fluid, etc may help...
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motoXracer971
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9/14/2015 7:45pm Edited Date/Time 9/14/2015 7:46pm
Sure it's not the caliper itself? What year is it?
user760a
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9/14/2015 7:51pm
This is an 09 model. Everything is in good shape- not dragging due to seizing caliper or anything. stock rotor is in decent shape, no tweaked or anything (that would cause drag)
motoXracer971
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9/14/2015 7:55pm
user760a wrote:
This is an 09 model. Everything is in good shape- not dragging due to seizing caliper or anything. stock rotor is in decent shape, no tweaked...
This is an 09 model. Everything is in good shape- not dragging due to seizing caliper or anything. stock rotor is in decent shape, no tweaked or anything (that would cause drag)
How long has it been that way? Have you ever worn pads all the way down before changing them?
Spooner
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9/14/2015 8:00pm
user760a wrote:
I really dont drag the brake too much, but I do use it to kind of stabilize the bike through a lot of corners. It gets...
I really dont drag the brake too much, but I do use it to kind of stabilize the bike through a lot of corners. It gets extremely hot and at that point,. even the lightest application of rear brake results in a chirp and lock situation. It is impossible to modulate the brake when it is that hot: its either no brake or chirp and lock the wheel. This is the story on a MX track- the other day in a two hour hare scramble with six laps of a nine mile course that has about 350 turns a lap (so it seems) I did not even make it through one lap before the brake was so hot it was all or nothing. It is impossible to flow when your rear brake is constantly locking

I have lowered the pedal (a lot) to avoid unintended brake drag. Have changed the brake fluid (just replaced with the standard dot 5) , and have even ground two quarter inch vertical grooves in my pads to aid cooling and lower friction a bit..all to no avail

has anyone had this problem? any tips? I am wondering if lower friction pads, extra insulators, a different fluid, etc may help...
If you used dot 5 fluid it will eat your braking system. Dot 3 or 4 is what you want, and if you are having these problems I'd use a race quality fluid (motul RBF, Silkolene pro-race, etc).

The Shop

Steadman
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9/14/2015 8:16pm
I am back brake dragger (woods rider mostly) I have found certain brake pads will accelerate heat especially aftermarket sintered pads. Try a kevlar pad and switch out to Maxima Racing Dot 4 (their high end stuff) This *should* cure your issue. Keep in mind kevlar pads don't bite as hard and will wear out quicker but they don't heat up as bad.

Like someone else mentioned…hope you didn't put DOT 5 in there Sad
user760a
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9/14/2015 8:23pm
I will try the kevlar pads. Now that you mention it, it did seem that the problem got a lot worse when i switched from stock pads to EBC sintered. I have even had my front brakes get hot enough to chirp and lock a little a time or two, though nowhere near as badly as the rear
...that's pretty bad
Spooner
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9/14/2015 8:26pm
So did you really use dot 5 in it? Maybe you used 5.1 which can work but a good dot 4 is better.
Steadman
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9/14/2015 8:34pm
user760a wrote:
I will try the kevlar pads. Now that you mention it, it did seem that the problem got a lot worse when i switched from stock...
I will try the kevlar pads. Now that you mention it, it did seem that the problem got a lot worse when i switched from stock pads to EBC sintered. I have even had my front brakes get hot enough to chirp and lock a little a time or two, though nowhere near as badly as the rear
...that's pretty bad
That exactly what I have experienced. Stock pads work fine, instant issues with EBC sintered. Depending how often you ride, keep up with bleeding your brakes. I got lazy this year, didn't keep up with it, boiled my rear brakes within 20 minutes of a 2 hour race. Made things interesting that's for sure. Lesson learned.
Trent179
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9/14/2015 8:57pm
I run the ebc Kevlar pads on the rear of my kx450f for this very reason. I am really bad about dragging brakes through corners. I have tried and tried to break from the habit but I just can't help it. Those shity grabbing black and red pads are the only thing that keeps my fluid from boiling every race. Lol. I'll be interested to hear if anyone else has ideas....
josh8811
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9/14/2015 9:00pm
I didn't know there was an issue with dot 5... I know my 300 brakes need to be serviced.. at least 100 hrs on the pads and fluid.


Whats wrong with dot 5? What the difference?
Zaugg
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9/14/2015 9:01pm
Definitely check to make sure you're not using DOT 5.

Also, look into Galfer Semi-Metallic or their Sintered Ceramic. Their quality control is way better than EBC and they're about the same price.

I'd also check to make sure your rear rotor isn't bent or warped.

mb
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9/14/2015 9:26pm
Could be the quality of fluid, I suggest Motul RBF600.
mnomis484
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9/15/2015 3:44am
You can mix DOT 3, 4 and 5.1
DOT 5 i believe is silicone based, so doesnt work on our bikes.
mmcmx
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9/15/2015 4:21am Edited Date/Time 9/15/2015 4:23am
An oversize reservoir cover might help too. I would assume the stock brake line from an 09 is not righid enough anymore too.
9/15/2015 4:35am
mnomis484 wrote:
You can mix DOT 3, 4 and 5.1
DOT 5 i believe is silicone based, so doesnt work on our bikes.
No, no. You cannot and should not mix Dot5 with any 3 or 4. All 5 is silicone based fluid.
Spooner
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9/15/2015 4:58am
I'm betting you have or did have a Harley? They are about the only thing you see with dot 5. You will want to rebuild the entire braking system before switching back.
mb
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9/15/2015 7:02am
thephoenix wrote:
No, no. You cannot and should not mix Dot5 with any 3 or 4. All 5 is silicone based fluid.


user760a
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9/15/2015 7:51am
Lots of good info here, it seems that I am not alone with this issue. I will double check which fluid I used. It may have been 4 or 5.1 because I do not think there are any issues with the fluid I am running aside from the possibility that it is does not have an optimum boiling point. I want to say it was also a little red and white EBC bottle, probably dot 4 ..I just had dot 5 on the brain?

to answer another question or two, my rear rotor is not in bad shape, its pretty well used but has not been run metal on metal nor is it warped/bent.

I will have to say, these sintered EBC pads may be the bulk of the issue. I bought them because stock pads were something stupid ..maybe $65 or so.
I am going to change pads and research some better fluid an d see how it goes. possibly even the magnum pads with the little radiator built on. has anyone tried them?
user760a
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9/15/2015 7:55am
ok thanks for the link to the magnum pads. it sounds like a magnum pad in a kevlar material would be awesome. may try the full metallic anyway
TBO
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Powell, OH US
9/15/2015 9:36am
I don't have that problem on my KX but I have had several guys tell me to ditch the stock plastic rotor guard because you will overheat the brakes.
user760a
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9/15/2015 10:00am
I actually have a beefy TM designworks plastic guard on my rear rotor, maybe I will ditch it, though. This past sunday was probably the most frustrating race ever and I am not going to repeat that mes again
9/15/2015 10:19am
Got any pics of it? Wondering if someone can tell more from a visual.
cwtoyota
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9/15/2015 12:24pm
thephoenix wrote:
No, no. You cannot and should not mix Dot5 with any 3 or 4. All 5 is silicone based fluid.
mb wrote:
[img]https://p.vitalmx.com/photos/forums/2015/09/15/105005/s1200_image.jpg[/img]


I believe the silicon based DOT 5 brake fluid is used by some top teams for it's higher boiling point. I may be mistaken on the source, but I think I remember hearing Tony Berlutti suggest switching to DOT 5 brake fluid on the PulpMX show a year or two ago.

DOT 5 can be used in our bikes but you have to completely disassemble the brake system and clean all of the DOT 3 / DOT 4 fluid out of it before using DOT 5. That would be a serious undertaking. You would pretty much have to rebuild the entire M/C and Caliper. Cleaning out and drying the brake line would be a real pain.

The only real bummer about DOT3 / DOT4 / DOT5.1 fluid is the fact that it is hygroscopic. That means it readily attracts and absorbs atmospheric moisture. So you have to change out the fluid from time to time.

Before posting I figured I would check my "facts"... This came up in a search from Summit Racing:

DOT 3, DOT 4, and DOT 5.1 brake fluids are glycol-based compounds that are compatible with one another. On the other hand, DOT 5 brake fluid is silicone-based and should never be mixed with any other type of brake fluid. DOT 3, DOT 4, and DOT 5.1 brake fluids will damage painted surfaces. DOT 3 and DOT 4 fluids have lower boiling temperatures than DOT 5 and DOT 5.1. Furthermore, DOT 3, DOT 4, and DOT 5.1 fluids are hygroscopic--they absorb moisture from the air. This causes the fluid to turn dark, indicating that it is time for the brake fluid to be replaced. DOT 5 fluid will not damage paint, has a boiling temperature in excess of 500 degrees F, and is not hygroscopic





KTMShane699
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9/15/2015 12:34pm
cwtoyota wrote:
I believe the silicon based DOT 5 brake fluid is used by some top teams for it's higher boiling point. I may be mistaken on the...
I believe the silicon based DOT 5 brake fluid is used by some top teams for it's higher boiling point. I may be mistaken on the source, but I think I remember hearing Tony Berlutti suggest switching to DOT 5 brake fluid on the PulpMX show a year or two ago.

DOT 5 can be used in our bikes but you have to completely disassemble the brake system and clean all of the DOT 3 / DOT 4 fluid out of it before using DOT 5. That would be a serious undertaking. You would pretty much have to rebuild the entire M/C and Caliper. Cleaning out and drying the brake line would be a real pain.

The only real bummer about DOT3 / DOT4 / DOT5.1 fluid is the fact that it is hygroscopic. That means it readily attracts and absorbs atmospheric moisture. So you have to change out the fluid from time to time.

Before posting I figured I would check my "facts"... This came up in a search from Summit Racing:

DOT 3, DOT 4, and DOT 5.1 brake fluids are glycol-based compounds that are compatible with one another. On the other hand, DOT 5 brake fluid is silicone-based and should never be mixed with any other type of brake fluid. DOT 3, DOT 4, and DOT 5.1 brake fluids will damage painted surfaces. DOT 3 and DOT 4 fluids have lower boiling temperatures than DOT 5 and DOT 5.1. Furthermore, DOT 3, DOT 4, and DOT 5.1 fluids are hygroscopic--they absorb moisture from the air. This causes the fluid to turn dark, indicating that it is time for the brake fluid to be replaced. DOT 5 fluid will not damage paint, has a boiling temperature in excess of 500 degrees F, and is not hygroscopic





You can avoid the compatibility issues by using Motul RBF 600 which has a 600 degree boiling point. Some of the best brake fluid around.

Shane
user760a
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9/15/2015 2:30pm
OK, I ordered some maxima dot 4 racing fluid , which also claims to have a boiling point of 600 degrees, and a set of carbon/kevlar brake pads. I am also going to get some of the magnum pads to test. I am on the fence about removing my TMD rotor guard, though. i kind of need it!
josh8811
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9/15/2015 5:40pm
This turned out to be a good/informative post!!

One more idea that I dont think has been suggested: Adjust your lever down a little.. Maybe 1/8"..

I know control setup is one of the most personal things about your bike, but I have read that its usually best to have your brake level with your peg.
BobbyM
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9/15/2015 6:35pm
user760a wrote:
I really dont drag the brake too much, but I do use it to kind of stabilize the bike through a lot of corners. It gets...
I really dont drag the brake too much, but I do use it to kind of stabilize the bike through a lot of corners. It gets extremely hot and at that point,. even the lightest application of rear brake results in a chirp and lock situation. It is impossible to modulate the brake when it is that hot: its either no brake or chirp and lock the wheel. This is the story on a MX track- the other day in a two hour hare scramble with six laps of a nine mile course that has about 350 turns a lap (so it seems) I did not even make it through one lap before the brake was so hot it was all or nothing. It is impossible to flow when your rear brake is constantly locking

I have lowered the pedal (a lot) to avoid unintended brake drag. Have changed the brake fluid (just replaced with the standard dot 5) , and have even ground two quarter inch vertical grooves in my pads to aid cooling and lower friction a bit..all to no avail

has anyone had this problem? any tips? I am wondering if lower friction pads, extra insulators, a different fluid, etc may help...
Bet yer brake lights are on while you drive down the freeway... Drive like a girl. Smile

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