Disk Brake Heating Up

Unicycles and Equipment
20

Sorry, that’s just blatantly wrong. Excessive heat is a problem with brakes.

It causes:

  • Brake fade from pads getting too hot
  • boiling brake fluid, leading to spongy brakes
  • Seals in the brake starting to leak quickly
  • Brake disks overheating and changing their material properties leading to rust
  • as mentioned in this thread: brake disks deforming. The material expands, and since it has nowhere to go radially, it will become wavy.

If you are not experiencing problems, it’s because you are not going fast enough to get the brake to it’s limit. It’s simple physics: when you go down a hill at constant speed, you are converting potential energy from height into heat by using your brakes (and some rolling resistance, leg muscles and wind resistance.) The faster you go, the faster you produce heat, and the hotter your brake gets, since it can’t transfer the heat to the atmosphere fast enough.

“a disk brake”. Look up some tests, and you will find that different models of brakes have very different capabilties, especially when it comes to when they start fading from heat.

That could be a problem, and should definetely be done. But the problem of a disk getting wavy is a real one, and while readjusting the brake may reduce it, it will remain a problem.

21

Thanks very much, Bristlecone and Finnspin! I appreciate your help.

I’ll double check tomorrow, but I’m pretty sure that my disk is not warped and that my pads are not touching the disk when disengaged (maybe there is just a tiny bit of rub, but it’s imperceptible and it’s #$%&@ hard to adjust to the point that there is zero rubbing).

I think I’m going to simply take the muni to a quality mountain bike shop in San Jose and have them double check the setup and the durability/quality of the brake system that I have relative to better options that may be out there.

I’ve been starting to ride down more and more hills, and it’s only this one really steep hill that gives me problems. But, it gives me problems every time and I’m starting to ride down this hill three times a week.

22

OK, went to La Dolce Velo in San Jose. This bike shop has great reviews and the mt bike guy that helped me really new his stuff.

He suggested a 203-mm disk. I’m going to get the Shimano XT RT86L 6-Bolt Ice Tech Disk ($56 US). I really stressed how important it was for the break to be forgiving (can’t be jerky). He suggested the TRP Slate T4 Brake ($120 US). These brakes have 4 pistons rather than two, and the guy said that this was an important improvement given that I said control and not overheating were my two big needs. I’m a bit nervous because reviews online say the brake does not have as much braking power as more extreme downhill mt bike brakes. However, all reviews talk about how good the control is with these brakes: “The modulation is incredible, with a smooth and linear power curve that is highly predictable. If TRP could somehow retain the G-Spec Slate’s class-leading modulation while offering a little more ramp-up in power, I could see these going to the next level. As it stands though, these are a reliable and well-priced trail brake for those who value feel over outright stopping power.”

All my fingers are crossed on how well all this stuff will fit… It was all ordered online (but I just put a bit down)… I’m going to have the bike shop install the brake. So, I need to wait until mid-May to get them on the muni…

I’ll report back in!

Oh, one more question, the guy also suggested metal pads over ceramic. He said that the metal may be noisy, but will be better. Does anyone know how noisy metal pads are?

23

The larger 203mm disk makes sense because of the larger area to dissipate heat and the Ice Tech disks seem to have good reviews.
I changed my metallic/sintered pads for organic/resin to get much smoother and easier to modulate braking action. The organic will not last as long but are easier on the disk (less disk heat build up). They may fade more then other pads but for me I don’t go down hills more then about 1/4 mile or so anyway.

24

Some disk brakes squeel. I’ve had organic disk brake pads that did it, and metallic ones. It usually dissappears with either material after bedding them in for a while.

I don’t think the reduced power they talk about in the reviews will be an issue for you. 1: it’s probably stronger than your current one. 2: I found that the tire is the limiting factor in most conditions, not the brake. You can’t brake more than your tire, and for unicycling, when you need the most braking power is for very steep sections. For Mountainbikers that slow down from 50 km/h, the limit may be the brake sometimes, as they have to use them to slow down quickly for turns.

25

The brake will be fine. As said the 203mm rotor will take a lot of heat. One thing to consider is the D´brake adapter. Due to it´s construction it is by far not as stable as a welded brake mount. It tends to vibrate which you will recognize as noice (must not be, but likely, especially with the large rotor using another adapter for the brake-caliper). If you recognize this, it is most likely not your pads and you should consider this easy fix:

post #57:

26

From my experience, “noise” isn’t the best description for what can happen with a flexing D-Brake. Massive vibration under my butt, and not in a pleasant way is what I had, before I made up a “Hugo strut” as kunstrasen linked to. But not everyone has that problem, it’s highly dependant on your brakes, pad material, frame stiffness, riding technique etc.

27

Does anyone know of a good torque requirement when tightening the bearing housing screws on the KH frame? On the KH website, the only guidance given is:

“… tighten the bolts with slight hand pressure. To test whether the bearing housing bolts are too tight, give the wheel a spin. The wheel should spin freely. If it does not turn perfectly freely, the bearing housings are too tight, and should be loosened slightly. Overly tight bearing housings will damage the bearings, and will not be covered by warranty.”

Since I’m going to have a bike shop install the disk brake, I know that most of the mountain bike components provide torque requirements and the tech’s are used to tightening screws to a required torque. Without a torque requirement, I could imagine the tech being ignorant about uni’s and cranking on the screw to the point of damaging the bearing.

(I searched the forum, but could not find a discussion about torque requirements.)

Thank you!!

28

[QUOTE=SanJoseUnicyclist;1704455]
Does anyone know of a good torque requirement when tightening the bearing housing screws on the KH frame? On the KH website, the only guidance given is:

“… tighten the bolts with slight hand pressure. To test whether the bearing housing bolts are too tight, give the wheel a spin. The wheel should spin freely. If it does not turn perfectly freely, the bearing housings are too tight, and should be loosened slightly. Overly tight bearing housings will damage the bearings, and will not be covered by warranty.”
Cut…/QUOTE]

I think the spin free method is the best. Just direct anyone messing with it not to over tighten.
Unless you do like I did, then you can torque to the limit of the fastener.

29

I think the spin free method is the best. Just direct anyone messing with it not to over tighten.
Unless you do like I did, then you can torque to the limit of the fastener.

30

It’s too little torque for most torque wrenches. So the KH instructions are the best guide there is. You should also make sure the D-Brake adapter is installed correctly. (Tighten the back bolt all the way down first, then snug up the front.)

With the amount of instruction you’ll have to do for the uni specific parts, I’d just have them install the disk on the wheel, and shorten the lines, then do the rest myself.

31

Ok, I finally have my new brake and have put a couple hundred miles on it.

Here is what I purchased:

  • 4-Piston Caliper: TRP Slate T4 Four Piston Caliper (front) for $120 US
  • 203-mm Rotor: SHIMANO XT SM-RT86 6 BOLT ICE-TECH ROTOR for $57 US
  • Metal brake pads with cooling fins: Shimano H03C Metal Brake Pads with Cooling Fins for $30 US

Total was $210 + tax and $60 for install.

Am I happy? Yes and no. First, I figured that with 1) a 203-mm rotor, 2) a four-piston downhill mountain bike caliper, and 3) metal brake pads, that I’d notice a huge difference in braking power (by this I mean less force on the brake lever with my finger for more braking force). However, the braking power of this relatively expensive setup is very similar to my original Shimano BL-M445/7L Disc Brake from Unicycle.Com. As a matter of fact, after this first-hand comparison I’d highly recommend the Shimano BL-M445/7L Disc Brake from UDC for most riders.

The big difference is that my TRP/Shimano-Ice setup does not overheat at all. I have ridden these steep/rocky hills (>20% grades) 3 to 5 times per ride about 3 times a week with no overheating issues.

But, there is one huge caveat! The brake chatter that Kunstrasen and others mentioned is very real with the 203-mm rotor. If I had to do it all over, I’d stick with the smaller rotor. The brake chatter that I experienced with the 203-mm rotor was severe and I could not ride a couple of feet down the steep grades without being tossed. The only solution was to use Kunstrasen’s support bracket design. THANK YOU for the design tip!!! I’d be out of luck without that bracket.

My big takeaways:

  1. Don’t get a 203-mm rotor

  2. The TRP Slate T4 has incredible modulation. So good that I can switch hands during the steepest parts of these declines. I feel modulation is extremely important for muni.

  3. Don’t hesitate to get metal brake pads. I don’t think they are overly aggressive! I’m amazed that I can’t tell the difference between the original Unicycle.com brakes and these expensive brakes (other than the fact that the expensive brakes do not over heat!).

32

Good to hear the overheating is solved!

As I mentioned, I had that brake chatter with a 180mm rotor, so I’m not sure it depends on brake disk size alone, but probably more on pad compound, frame stiffness etc. The support bracket will also help the Adapter not break (which they sometimes do), so it’s definetely worth it for anyone.

I’m in the market for a good 4 piston brake (well, that’s when I have some money to spend), so I can add the slate t4 to the list of candidates now. How far away from the seat does the brake lever end up?

33

Thanks for pointing that out, Finnspin!!! (I did not take the time to re-read the entire string before posting and missed your post. Sorry about that.)

You should read the reviews on the T4. If I remember correctly, they talk a lot about how great the modulation is. I thought modulation would be important because with my old brake I would have to be very careful about not over-breaking when first engaging the brake. With the T4, I can brake hard even when first engaging the brake because it is so forgiving.

BUT!! I’m guessing that the T4 gives up braking force in order to have improved modulation. The reviews say that the T4 does not have good braking force. (I read the reviews a long time ago, hope I’m remembering correctly…)

I have to admit that I wonder what the best Shimano four-cylinder caliper would be like! My understanding is that it has great force, but who knows about the modulation.

I find this topic all very interesting, but frustrating because there is such little data/experience out there with these brakes on unicycles. Thus my motivation for posting about my T4 experience.

34

If it comes to 4 piston brakes I can recomment the Shimano Saint. It has excellent braking power and great modulation. Very easy to control. Due to he solid caliper design plus ceramic pistons it has also no overheating issues at all.

35

Yeah, I sort of wish I bought the Saint!

Does anyone have first-hand experience comparing the difference between ceramic and steel pads on a uni? I’m curious how big of a difference you actually feel on a muni.

Also, as mentioned above, I have the T4 caliper with steel pads. I was concerned that the steel pads would be too aggressive and cause me to stop too quickly (low modulation). Not the case. I feel I could still use more braking power. I believe the reviews for the T4 caliper say that it does not have as much braking force as other calipers. So, I’m wondering how much of the lack of braking power/force that I feel is due to a single brake on a 29" unicycle while going down a 25% grade, or how much is due to the T4 not having as good of braking force as the Shimano Saint.

36

On mtb in the past I did compare the original organic vs metal pads on a shimano XT. My feeling was that the modulation is a bit better on organic. The braking power is lower on them. In case of vibration the organic can help, they tend to be quiter. However, I did not have noice with the metal pads as well. As braking power is higher and the wear is much lower on metal, I stayed with them.

There are other pad makers as well. One of the best tested (high power) were always the trickstuff brake pads (available for most current brakes). I have no first hand experience here.

On the Muni I never changed the original Saint metal pads.

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37

Well, I’ve been on a journey dealing with brake chatter from this 203 mm disk. Before I get into it, I’d like to thank kunstrasen again for sharing the design to stiffen the D’brake adapter’s large cantilever arm.

I copied Kunstrasen’s basic design, but since my son has a 3D printer, I thought I’d design a nice (plastic) bracket to clamp onto the KH frame. Also, I noticed that one of the M6 threaded mounting holes on TRP’s “disk brake adapter” (a.k.a., the standard mountain bike bracket that fastens to Unicycle.com’s D’ Brake Adapter to position the brake caliper at the correct location for the 203mm disk, phew…) was nicely pointed in the direction of the KH frame.

So, I though I could easily lengthen the M6 screw and then hold the extended screw with the 3D printed bracket mounted to the KH frame. The design worked sort of nice. Check out the pic below:

The problem was that I did not buy a longer M6 screw. I tried to wedge a rod between the 3D printed bracket and the “disk brake adapter”. (Figuring that the rod would always be in compression.) After a few rides, the relatively flimsy 3D printed bracket became lose and the rod fell off.

So, for the 2nd design attempt, I still used a relatively weak 3D printed bracket, but this time I got rid of the original M6 socket head cap screw and bought a 4" long M6 threaded rod. I then used the threaded rod to mount the Slate T4 caliper while the 3D printed bracket held the other end of the threaded rod (still just used compression between the 3D printed bracket and the threaded rod). Two pics below:

This worked great for several weeks. But, I’ve been braking pretty hard and either from yielding the plastic bracket, or creep, or low cycle fatigue, the 3D printed bracket started to twist on the frame and under really extreme conditions I could hear the brakes start to make noise (I believe this is the precursor to chatter once the bracket became even looser).

So, I bit the bullet and redesigned the bracket out of aluminum. I know that the bracket is huge, but this 3rd try has got to work! Also, I’ve threaded the M6 rod into the aluminum bracket. Super stiff… Below is my final design. if this does not work, I’m biting the bullet and buying a 180 mm disk and the Shimano Saint caliper…

Look at how little clearance there is between the disk and the bracket. Hope this is OK. It was Ok for ~6 weeks of riding with the plastic bracket (and that bracket had even less clearance because of thicker walls).

In a few weeks, I’ll let you know how this works. My guess is that it’s going to be super solid and I’ll be able to brake hard and fast with no chatter!

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1 Like
38

Wow. Looks like you spend a lot of work and time.:slight_smile: Maybe buying a disc frame (e.g. Oracle frames are not too expensive, at least here in Germany) would have been easier. But that is just a boring stock solution.:smiley:

Good luck with your latest version. Looks pretty solid to me.

39

An interesting fix for the poorly desiged D’ Brake Adapter. I think a welded bracket on the frame would have been better and it would be a lot easier to remove the wheel when needed. A good tig welder could add a bracket on the frame for a clean solution to the problem.