Avid BB7 issues
 

Rode with my daughter on Thursday and had to stop quickly for a light at the bottom of a 47mph descent. The rotor got red hot and the brakes screamed. After that it sounded as if the brakes where metal on metal with a horrendous grinding noise. I thought the pads must have been wasted but when I pulled them they where not. The bike has just shy of 160 miles on it so I believe pads where bedded.
The pads look ok (very discolored though) and the rotors look gouged. Stopping power from the front seems vastly diminished. Do I need to replace pads and rotors or is there something I can do to restore them?

Team weight on this descent is @480
Bike is Cannondale RT2 with stock BB7s and Avid 203 rotor

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Run them. The photos do not show anything that would concern me. Yes they do get hot at that speed and mass to stop. Often the brakes are used casually and seldom see had braking.

You have sintered metal pads on a metal disc. The few gouges are there and will be fine. As for the howling and screaming, sometimes the brakes are not clean, especially if the timing chain has or careless chain lubing has contaminated the disc. The brakes may have had a hard time building friction and this did not help matters. Even dust from the brakes and road will lessen the brakes effectiveness.

In regards to lost performance concerns, clean them and reinstall. Make certain the vibrations did not shift the caliper on the spherical mounts. If they got hot enough to melt the adjusters, replace them. Honestly, I do not even see abnormal overheating or discoloration of any concern.

FWIW, I just had a look at he discs on both tandems, we have more "lines of use" than the photo you posted.

PK

Paul covered most of the key points...

You just experienced brake fade; congratulations!

The high heat caused the pads to outgas and glaze and your brakes probably lost stopping power during the latter part of the descent.

You can either be patient and let normal use remove the glazed surface or you can put a piece of 180 or 200 grit sandpaper on a flat surface and lightly sand the face of the pads using a circular motion to remove the glaze. You might also want to clean the rotor with some alcohol or brake cleaner. After a few stops with the resurfaced brake pads your brake performance should return to normal.

I'm surprised you experienced fade after what sounds like one stop from high speed, but I'm not an expert. Long term you might consider changing the rotors out to Shimano ICE XT. Several here are running these and have found them to be superior to the stock Avid rotors. It appears you have discs front and rear so I don't have any directly relevant experience having a disc only on the back.

It's physics: note the team weight of 480 lbs.

Yep, try over 500 lbs at 60mph. I'm lucky enough to still be alive after that one!

This was the final of three descents over a short period so that may have contributed to it.
I do have the XT ice rotors and ebc gold pads I had picked up after reading about potential issues but just not installed as of yet as I wanted to give stock a chance.

http://bikeforums.net/attachment.php...hmentid=292104

Sorry my friend but if that were us, I would make adapters for Brembos.

PK

I have never ridden with you so just a suggestion, how much front brake was applied? You really need both brakes working hard for those stops. Did the front fade also?

again, as TandemGeek said, welcome to brake fade. It can happen. Consider also, if these were hydraulic brakes, you probably would have boiled the fluid.

PK

I should have clarified, the photos and issues came from the front. I was applying pressure about 60/40 front/rear. It was only the front which experienced the fade. Inspection of the rear indicated no where near the heat generated as it is not discolored like the front

Yeah I hear ya. Didn't know any better at the time.

I believe the stock Avid pads are actually called "semi-metallic" (yours) or sometimes "organic" is used, not a full-on metalic pad like the EBC Gold. The minor scoring seen in your rotor photos appears to be normal.

Try installing the ICE rotor with a set of new Avid pads (do not reuse the old pads with a different rotor) if you have them, which will produce less wear on the rotor than full metallic pads. Thing is, the ICE rotor produces much less heat, so the default Avid pads work better and should last much longer.

I've only ever replaced one set of semi-worn Avid pads just because a couple years had gone by and wanted to test performance with a few other types. We seem to get very extended usage out of our stock Avid pads and my stock of spares remain in my parts bin for ages. Regardless, if we were planning a decent of Mont Ventoux I'd swap in the EBC beforehand.

The semi-metallic and organic pads are two different compounds. Stock pads are semi-metallic.

It's a problem. Rotors are very low mass and heat quickly. Rims have a much larger mass but overheating can blow a tire, which is also not good. I have rim brakes and there are just certain descents I don't do on the tandem, though they are no problem on a single. If I have to do steep descents, I put on the rear wheel with the drum brake. We can handle anything with rims and the drum.

There was a recent huge argument about this over on the touring forum. Clearly there are people who have had stopping problems and got religion and there are those who have not. A riding buddy with a BB7 rear disc smoked the disc and went off the road on a rather short but very steep descent. His front rim brake failed entirely, his fault, but now he won't ride the steeper ones with me any more, even if I only have rims. Caution is good.

Our tandem has a more even weight distribution than a single but the long wheelbase decreases weight transfer. I brake about the same front and rear because it's much more of a heating problem than a traction problem. Other people's experience on that?

Was this on a tandem? Where was this? There are some short, steep hills that frankly, scare me and I am very careful to hold the speed down and not let the bike get away from me (the descent on S Juneau St to Seward Park is an example.)

When we are running steep grades, especially with the bob, I am constantly thinking about brake heating, tend to follow your example, same front and rear and I also tend to alternate between front and rear to keep temp in check. I suppose I "ignorantly" think we can probably stop once, if temps are held in check, but if the heat builds due to "drag braking", one may not get that stop.
R&J

Select a disc with more surface area. Might help.

Yes, on a CoMo Speedster. On what we call Golf Course Road, but is really 240th St. SE, off Bostian Rd., north of Woodinville. I had two tires blow on that descent on our Speedster before I got my tire/rim/rim strip combination sorted, luckily not during the crux part, but a few seconds later when it was safe. Juneau is not so bad, but it's good to get descending chops to be habits. I've only taken that one from the south. I let it build pretty good on Seward Park, maybe braking hard a couple times, then brake hard before the right hander, then mostly drag them down Juneau, braking harder at the bottom.

Ok,
Used 180 grit sandpaper to try and resurface the pad then tried to re-bed them. Put another 25 miles on it and the front brakes still scream/grind like a banshee. I am going to install the ICE rotor on the front for now (only have one set of new avid pads) and see how it goes.

On a similar note, since the cannondale is setup for disc/v-brake would it be prudent/is it possible to add a stoker controlled V-brake

If all else fails, try this stuff:
http://www.gravelbike.com/?p=1177

Hmmm... I've never heard of Squeal Out, maybe it's worth a try?

It worked on my BB7-equipped commuter.

Last year we took our RT2 on the RSVP (Ride from Seattle to Vancouver and Party). This is a 185 mile ride over some flat terrain and some hilly terrain, but while there are some short steep descents there are no long steep descents. By the end of the trip the rear brake on our bike was squealing loudly although it was stopping the bike. Pads and rotors looked like new. I did some research and decided to replace the stock metallic pads with the organic ones. OK, not too hard a job. But after the replacement pads were in the bike continued to squeal. I was beginning to get irritated! I took everything apart and reinstalled the pads, but this time I noticed they felt "different" when they seated. This time no squeal at all. I now believe it is easy to get the pads into the holder such that they are not perfectly parallel to the disk. These parts are small and my eyes are not young anymore so it is easy to miss this. What caused the pad to be seated at an angle to the disk? Good question. When the bike was brand new a few of my friends with really good ears noticed a "whispering" sound from the back of the bike. I adjusted the pad out one click and the sound went away. On the RSVP I always alternate front and rear brakes to try to prevent fade. Maybe engaging too fast causes the pad to "jump" out of alignment. Bottom line is I don't know what caused it. I now believe the original metallic pads were OK if they had been seated properly. But the non metallic ones are working so well that I am not going to tempt fate by replacing them. We are a 330# team.

There's no reason you can't add a rim brake. One caveot is that you shouldn't use it like a drag brake. But you could use it to alternate braking for heat management.

There could be an issue with locking the rear wheel, leading to a slide in an emergency situation, but some communication could manage that.

I would be really reluctant to do that. If you're going to add a rim brake to the rear I would suggest using it as the primary brake and setting up the disc as the drag brake (that's the way ours is set up.) I also would retain contol of both rear brakes because it's too easy to apply too much braking with a disc.