Oracle disc brake problem - help me please!

I’ve been a proud Oracle (24) owner for some time now and I’ve learned to ignore the squealing the disc makes at very low speeds (fairly recent problem). Of late, however, my disc has been acting up a bit; the small scraping of one of the pads has turned to severe drag to the point where I’ve had to take my calliper off.

I though about putting a spacer between the D’Brake and the calliper adapter (post to IS) but the rubbing is coming from the outside pad as shown in the image below. Everything’s installed correctly and the brake is in good condition so I cant see why it would rub.

Another problem I’m having is with the pads themselves. A while back I noticed that my rotor had a black line about 2/3rds of the way from the outside edge which I assume is due to uneven pad/rotor wear. This isn’t much of a problem as my brake’s still pretty beefy (especially since I just wiped my pads down with water to get rid of the gunk).

What is a real problem, however, is the noise my brake makes. Occasionally my brake loses power and starts making this - to put it bluntly - ‘wet fart’ sound. It’s not just a sound though, you can feel it as if there is something catching on the rotor’s holes.

Does anyone know what might be causing these problems?


Looks like you have a stuck piston. Take the caliper off and press the piston back into the caliper with the flat side of a screwdriver. Keep the screw driver between the pads(or stick the rotor in between) and press the lever, gently!! see if the pistons both move equally. Grit gets in there. Sometimes just moving it in and out gets it unstuck, otherwise a rebuild is in order. The sound maybe glazed pads, try sanding with 220 wet dry emory paper, clean them and the rotor with isopropyl alcohol NOT water. You may have to shim the caliper to get the rotor centered just right. They make shims or use aluminum from beer cans (soda cans may work, but I have no experience with that:D)

With the pads in, or out?
Can’t shim it, the rub is on the outside. Shimming it would push the problematic pad closer to the rotor.

It shouldn’t matter if the pads are in or out as long as you’re careful not to scratch them with the screwdriver. If you’re worried about it, take the pads out. Also you might be able to use a plastic tire lever instead of the screw driver in there.

Check to see if the D-brake mount is bent. Mine rubs on the disc and is the biggest pain in the ass ever. I honestly dont know why there is only one frame out there that has a disc brake tab welded to it. The D-brake tab is pure shit, sadly its the only thing you can use unless you have the KH setup.

I’ve bent three D-brakes. It’s just not meant to take super hard stops that we throw at it.

Is there any way to tell if it’s bent (maybe tke it off and rest it on a straight edge)?
The fact that the D’Brake is being slagged off is a bit disconcerting considering that my next uni will probably be an Oracle (frame only) as the KH29 frames are out of stock here. :frowning:

“bent D Brake”?

I can’t imagine bending one, breaking one maybe, but bending aluminum usually results in cracking. They can shift, so you could try adjusting it on the frame, shimming the caliper on the D Brake mount is also a way to re-establish the correct alignment.

It appears that your caliper is to close to the disc, so can you move it outboard any further? If youhave maxed the outboard positioning, then you need to shim it OR add a 2mm spacer between the hub and bearing.

Also, the Bengals are a basic disc brake, so the pads don’t retract well, it could be you have some junk under the pad, so a squirt of two of brake cleaner could help. It is also one of the problems I had with the Bengal and the reason I upgraded brakes.

Keep in mind that brake pads need to be removed and cleaned, i.e sanded down once in a while, esp if you ride in wet conditions.

Maybe it’s not the D Brake?

So for a more balanced persepective:

I have two Nimbus Disc brake set ups, one is a D Brake (Oregon), the other is a Nightrider 36er with a frame mount disc brake tab. I also have extensive time on two KH unis equipped with the D Brake (26guni, 29).

D Brake vs Frame mount disc brake tab:
Braking performance = No difference
Rubbing = No difference
Set up and adjustment = The D Brake is a a little more time consuming, but only because the brake position can change slightly when the wheel is removed or a swap wheels. The frame tab had to be shimmed initially to get the correct alignment.

Don’t fault the wrong equipment.

Disc brakes are notorious for being a pain in the arse, just ask any bike mechanic. So if you are having pad rub issues from alignment and/or squealing brakes, then consider the alternative: Magura rim brakes :frowning:

I have issues with my disc brakes from time to time; I sanded my Oregon pads last night, but my problems now are nowhere near as bad as when I had rim brakes. Rim brakes also squeal, and talk about rubbing, rim brakes rub so much that they can literally stop your wheel as you ride! Then there is the poor braking power and the absolute nil braking power when wet, etc, etc…

If you can’t fix your braking problem, don’t blame the equipment, instead head to your LBS and let them sort it out.

I have been riding the D Brake for muni for ~two years, three to four rides off road weekly, and I have yet to bend or brake a D Brake. The D Brake on my Oregon is the original D Brake, so ~200-250 days riding, and it works fine.

There is also another disc brake bearing holder mount, Mountain uni.

UCM alternative

Thank you Ben. I have never had a UCM come back for any reason, bent, cracked or otherwise. Not to say someone couldn’t try and succeed if that were the goal, but just saying. I would concur with Ben, I’ve been using a disc brake with UCM for 3+ yrs, and wheel swapping is the only activity that seems to require some tweaking. 29 & 36 Triton’s have tab mounts too.

How about a steel UCM? It would be harder to machine, maybe more pliable which could be a problem, but it coudl also be lower profile so improved clearance on rotor bolts…

I’m not saying I have a preference for either one, the frame tabs have their own issues with alignement and bending, which is why UDC went to the D Brake, but in some cases it might be worth the effort to have one welded on which is probably why some high uni frames have them included (Triton, KH).

the way i look at it if you break a tab off your frame your skrewed but if you bend a umc or dbreak its easy to replace just my thought.

See I though it sounded too bad to be true. :stuck_out_tongue:

Also Ben, do you know if you can run an outboard disc with the Oracle 29er frame. I.E are the bearing cups narrow or wide?

I’m assuming so, but I haven’t tried one yet; my 29 guni will be built on an Oracle 29 frame so it better work!

I think you have to run the brake on the opposite side or something like that, might also need to use some stainless steel washers to space the caliper correctly.

The KH frame can also be run with an inboard brake, just need to space out the caliper to fit.

Just for the purpose I put it through its not good. My unicycle doesn’t get treated to nicely one bit on the trail. You can clearly see that the D-brake tab is bent. I set the D-brake mount on a table that I know that is straight and the tab wobbles up and down. Lastly you can see the tab clearly rubbing on the disc. For gravity assisted riding it doesn’t matter, if im riding trails that are not heavily gravity assisted then you can clearly hear/feel the rub.

Also the D-brake tab sucks, (yes it sucks) because you have to tighten the crap out of the cap and you ruin bearings a lot faster. Either way I am sticking to my claims for the D-brake tab being at fault for a majority of my brake pains. Overall the positive perks of the disc is in such high standings that I will never switch back to rim brakes. Just a matter of time until more options are available for frames hopefully.

Everyone is talking about how D-brake tabs that are welded to the frame could brake off. How many people has that actually happened to?

The QX disc frame would be perfect: no Dbrake needed, disc mount on the left side for inboard discs. Does anyone know if they sell it seperately? I only could find the whole muni:

Their homepage only shows the non-disc frame:

Not sure if what you want can be purchased here, but this place has a ton of
QX frames. I don’t know if they ship international though.

@ Jacob,

I can’t see your pictures from work, but I’m assuming yours is bent or broken, so maybe you should buy one from MountainUni or get a tab welded onto your frame. I started keeping a spare D Brake in my gear bag after I saw a picture posted of a broken D Brake, but after two years my spare is still in it’s original wrapper.

All I’m saying is that I have been riding the D Brake since it was first released and it is mostly plug and play. I’ve swap wheels on my Oregon dozens of times, pulled the wheels to swap tires, etc… and rarely do I need to adjust the brake.

I find that aligning the D’Brake and Caliper as a unit as I tighten the bearing cap helps with keeping alignment true. I do not overtighten the "adjustment bolt’ on the bearing cap, it hasn’t been necessary as the bearing cap is plenty beefy to hold to hold the wheel in place.

If I were having a new frame built or I was getting a frame powdercoated, I’d probably spring for a frame mounted disc brake tab, but for most people the D Brake works fine. As a retrofit, the D Brake is a great idea, but then that was it’s original purpose when MountainUni created it.

I believe the reason that UDC went to the D Brake was due to difficulties with maintaining consistent manufacturing tolerances from afar (Taiwan). I got one of the last frame mount tabs and Josh said he had to search through their frame stock to find one that was straightish, but he still had to cold bend the mount and I still had to shim the mount with washers to get the correct pad angle.

Perhaps Nimbus will shift to a frame tab over time?

It might be bent, I’ll have to check next time I get my uni out. TBH though, I can’t see how it could’ve been bent. The problem seems to have crept in slowly and I can’t remember banging my D’Brake hard or anything.

As for the UCM or disc tab, they’re both expensive and I’m taking the disc off this uni anyway and putting it on my 29 (that will be arriving soon).