Mountain Bike Reviews Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
60 Posts
Discussion Starter · #1 ·
2003 Truth, Hope Mini Disc Brakes. I weaigh in at about 185.

On a ride yesterday we had the end of the ride in sight. 2600 vert. below us, pretty steep, lots of switch backs.
About 1/2 way through, my rear brake began to fade. If I kept pumping it would still hold but if I quit for more that 30 sec. the lever would run through the cycle nearly to bottom before it would engage. I could pump it back up to pressure.

When I reached a flatter section I stopped to see if I had blown a line or what. The unit was dry but pretty hot. I had a few Oz of H2o left in my Camelback so I spit a mouthful onto the assembly. It steamed right off. I repeated the process and was able to cool off the rear brake. (not the rotor but the Calipers)

1. What can I do to reduce this problem?
2. Is using H20 to rapidly cool the Brakes, bad for them. Will they suffer damage.
3. Are larger rotor Brakes less prone to this problem?

Thanks in advance.
 

·
Registered
Joined
·
9,987 Posts
hope minis are more of an XC oriented brake, so if you are intending to make this a regular loop you might want to consider upgrading to something designed for a more all mountain type of riding.

Larger rotors will help a bit as well.

I am a little concerned though if it was actually fade you were experiencing. Typeically when I have experienced brake fade the lever does not cycle through its travel, instead I get the feeling that no matter how hard I pull, the thing aint slowin down that much. I guess it was possible that you were actually boiling the fluid inside the system, but I am not sure if pumping would get it back.

Also try not to use as much rear brake. Therre is way more stopping power available on the front, and the steeper it gets the more I depend on the front. Are both your front and rear rotors 160mm?

Using water will not harm the system, but I would still suggest tweaking the system or your riding style (or a combination) rather then using water to "fix" it on a regular basis.

Fenske said:
2003 Truth, Hope Mini Disc Brakes. I weaigh in at about 185.

On a ride yesterday we had the end of the ride in sight. 2600 vert. below us, pretty steep, lots of switch backs.
About 1/2 way through, my rear brake began to fade. If I kept pumping it would still hold but if I quit for more that 30 sec. the lever would run through the cycle nearly to bottom before it would engage. I could pump it back up to pressure.

When I reached a flatter section I stopped to see if I had blown a line or what. The unit was dry but pretty hot. I had a few Oz of H2o left in my Camelback so I spit a mouthful onto the assembly. It steamed right off. I repeated the process and was able to cool off the rear brake. (not the rotor but the Calipers)

1. What can I do to reduce this problem?
2. Is using H20 to rapidly cool the Brakes, bad for them. Will they suffer damage.
3. Are larger rotor Brakes less prone to this problem?

Thanks in advance.
 

·
Magurified
Joined
·
483 Posts
It sounds like you boiled the fluid. Pumping the lever increases the fluid pressure in the line which increases its boiling point, but releasing that pressure lets the boiling point drop back down. Once you've boiled the fluid, it's knackered basically, and needs bleeding out.

Fenske said:
1. What can I do to reduce this problem?
3. Are larger rotor Brakes less prone to this problem?
Yes, larger brakes are less prone to it. They have more thermal mass, they cool better and they offer more power. That's what you can do to reduce the problem.

2. Is using H20 to rapidly cool the Brakes, bad for them. Will they suffer damage.
They can do. Water will not cool the brake evely, and rapid cooling of part of the brake but not other parts can lead to significant thermal gradients and consequently stresses things as cooler bits contract. Certainly you don't want to cool the rotor this way as the thermal stress can cause it to warp.
 

·
Registered
Joined
·
60 Posts
Discussion Starter · #7 ·
Thanks for the replies.

The bike in question is an EW Truth, an XC rig. I am an XC type rider. I believe the rotors are 140s.

The ride in question is one of many round here that have loooong climbs followed by looooong decents. I probably won't be doing that particular ride again til fall. (the bugs were horrendous).

The fluid in Hope Minis is DOT-5, about as tough as is made. How can I tell if it is spent?

Again, thanks.
 

·
Sirstopsalot
Joined
·
104 Posts
The guys at Galfer call it lever fade. You are boiling the fluid .I am 6 foot 6 inch and weigh 290 lbs and had that problem alot they said run DOT 5.1 fluid (higher boiling temp)and if that did not work then I could try there 8 inch rotor it runs cooler .I changed fluid rotor and pads there was a big change for the better :)
 

·
Magurified
Joined
·
483 Posts
Fenske said:
The fluid in Hope Minis is DOT-5, about as tough as is made. How can I tell if it is spent?.
I hope it's not DOT 5. I SERIOUSLY hope it's not. DOT 5.1 is what you want (which is VERY different to DOT 5). However, did you put the fluid in there yourself, because it could be DOT 4.

A 140mm rotor for a 2600' descent for 210# (you+bike+clothes, etc) is way under what you need. I understand that it is the rear brake, but even so, it's obviously not up to the task since you're running into the problems. There is of course the question whether it's worth going to a bigger and consequently heavier rear brake if you only have this problem once or twice a year.

One of the quickest ways to heat the brake up to temperatures where this can happen is constant dragging of the brake. Not necessarily braking hard, but just constantly... it gives the brake system no chance to cool itself.
 

·
Registered
Joined
·
3,143 Posts
Fenske said:
2003 Truth, Hope Mini Disc Brakes. I weaigh in at about 185.

On a ride yesterday we had the end of the ride in sight. 2600 vert. below us, pretty steep, lots of switch backs.
About 1/2 way through, my rear brake began to fade. If I kept pumping it would still hold but if I quit for more that 30 sec. the lever would run through the cycle nearly to bottom before it would engage. I could pump it back up to pressure.

When I reached a flatter section I stopped to see if I had blown a line or what. The unit was dry but pretty hot. I had a few Oz of H2o left in my Camelback so I spit a mouthful onto the assembly. It steamed right off. I repeated the process and was able to cool off the rear brake. (not the rotor but the Calipers)

1. What can I do to reduce this problem?
2. Is using H20 to rapidly cool the Brakes, bad for them. Will they suffer damage.
3. Are larger rotor Brakes less prone to this problem?

Thanks in advance.
What pads you using? I have Mono Minis and have cooked the brakes and never had any fading with the stock sintered pads. Switch the rear out with the organics and they fade a lot when they get hot.
 

·
Registered
Joined
·
60 Posts
Discussion Starter · #11 ·
Ratt, I think you nailed it. Just switched from Kool-Stops to Fibrax. Never had the problem before and I have done a lot of long decents on this rig w/o this problem.

Again thanks. I was going to do a Brake set overhaul this summer. Now is as good a time as any.:thumbsup:
 

·
Magurified
Joined
·
483 Posts
Fenske said:
Ratt, I think you nailed it. Just switched from Kool-Stops to Fibrax. Never had the problem before and I have done a lot of long decents on this rig w/o this problem.
What you've described is very much the behaviour of boiling fluid rather than glazed pads. However, the change in pads could have caused it if the Fibrax pads are significantly less good at isolating the caliper from the heat at the friction surface. For example, magura have heat isolators in their pads and warn against the use of third party pads which may not (In this case, I believe "heat isolator" means that the backing metal is chosen to be a poor conductor of heat, and the friction material of the pad is also a fairly poor conductor, such that the rotor is the "easier" way for the heat to go).
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top