Mechanical Disc Brake Lockup

[DJ Rider]

Was riding my Mongoose gravel bike slowing for pedestrians when the front mechanical disc brake locked up solid. Felt like I hit a wall and as I flew over the bars doing my impression of superman I could see the caliper side of the fork bend. As the wheel hit the frame the rotation force against the frame pulled the wheel out of the fork.
I didn't hit anything and the asphalt path was smooth as it gets.

Question 1: which I think I know the answer to is... How could the front wheel lockup hard and instantly?

My guess is a piece of the pad broke off and lodged in the disc brake, possibly the cooling slots of the disc ???

Question 2: has anyone ever experienced this or known of this happening to anyone else?

It's not an expensive bike but has served me well over the years. Obviously avoiding sudden wheel lockup from faulty brakes and the thrill of flight is the priority. Hitting the pavement was the least favorite part of the ride.

All the bike needs is a fork and a better brake.

 

[99t4]

Caliper photo is blurry but looks like something did take a chunk out of the inner pad? Also possibly the paint scar indicates caliper body bending or fracture? Hard to tell from your photos.

Do check the headtube welds and toptube/downtubes for bends at their connections to the head tube. Sometimes they look straight but flaking paint gives it away.

 

[Comrade]

My guess is a piece of the pad broke off and lodged in the disc brake, possibly the cooling slots of the disc ???

How close were your pads to the rotor? How long was the brake pull? They could have been very loose inside the caliper, then for some reason one pad decided to turn on an angle and catch a cooling slot on the rotor.

 

[lifepo4ever42]

its time to upgrade for hydraulic calipers

 

[amberwolf]

Question 1: which I think I know the answer to is... How could the front wheel lockup hard and instantly?

My guess is a piece of the pad broke off and lodged in the disc brake, possibly the cooling slots of the disc ???

That is probably what happened...but the fork being able to bend as shown means the fork isn't capable of handling the braking load (weight of the bike vs deceleration amount (speed change)). I've experienced a fork similar in appearance to yours failing at the crown/stanchion bend on my SB Cruiser trike--thankfully it was a gradual failure and I noticed it before it was catastrophic. The fork lasted me a couple of weeks from install till I noticed the failure.

The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier

And I forgot to say, In my experience, that kind of a washout was due to weight distribution. Not enough in the front. :D :bolt:

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It should look like this


it ended up like this, looks like the department store bikes that get their forks installed backwards:


I recommend the Avid BB7 MTN as a replacement caliper. They work fine for control and stopping power for my heavy-cargo trike SB Cruiser, even with shitty no-name replacement pads (much better with Avid sintered pads). Just make sure to get a *genuine* Avid unit, not one of the many clones that *says* they're made by Avid. Mine is used with a genuine Avid speed dial lever that makes it easy to setup for my ability to pull it.

If your rotor is not bent or otherwise damaged it can still be used with the new caliper. Otherwise I recommend a rotor with the most metal in it (the least holes, and the smallest holes) for the most braking surface / grip, in the largest diameter you can get for the fork you will use.

Note that some forks have a rotor size limit in their specs because they can't handle the torque from larger ones. (and that assumes a certain rider/bike weight and speed being stopped from--any of those being higher than the rating means the fork can't handle it either and might or might not fail at any moment during any braking event). If there are no ratings or specs for these then you have no idea what will cause the fork to fail or when, until it does.

 

[calab]

How was the maintenance on that Mongoose, who sells the Mongoose bikes?
Also, were ALL the components stock?
Where did you buy the brake pads from? Your local bicycle store or some mystery salesman on the inter-webs?
Same goes for the calipers and rotors.

It's not an expensive bike but has served me well over the years.

 

[richj8990]

its time to upgrade for hydraulic calipers

100% correct. I had mechanical disk brakes and the same thing happened when I was going a bit too fast down a rocky section. Over the bars and it was the worst accident I had, almost broke ribs. Back then going 'too fast' was going over 8 mph. With hydraulic brakes you can go twice that fast or more and still be fairly safe. And the pre-bled ones are plug and play. They are actually easier to install than mechanical disk brake calipers. They last for 2000-4000 miles before they need bleeding (or you just throw them in the trash and buy new ones). Zoom / ZTTO sells 4-piston hydraulic brake kits front/rear for under $100 and they are GOOD, I'm not kidding. They are a total steal. I like the modulation better than Tektros that cost twice as much. Good brakes and tires will really transform a bike especially offroad.

 

[amberwolf]

Hydraulics wouldn't have prevented this problem, which was a lockup of the rotor in the caliper apparently caused by a chunk of pad, so changing to them doesn't seem like it would make a difference here.

 

[amberwolf]

This past week, I had essentially this kind of pad failure on the SB Cruiser (but it's fork is sturdy and had no problems; instead the pad itself just ripped a chunk off and I lost about a third of my braking power, still leaving more than enough to lock up the front wheel with the Avid BB7 MTN calipers with 200mm rotor).

The cause of mine was the spring clip that pushes the pads apart / holds them against the calipers when not being used somehow touched the rotor, and bent and was welded to the rotor (probably all during that specific braking event).

This was at an otherwise unoccupied intersection on my way to work, so I pulled up onto the sidewalk there and checked the brake, not knowing the actual problem/cause, but concerned over the sudden change in braking power and the ticking noise (once per rotation). I didn't see the problem at that moment, and needed to get to work, and it was over 100F already out there, so I chose to reduce speed from 20MPH max to 15MPH max and continue the mile or so left to work, and coast down early to stops and use the regen braking to finalize them, avoiding use of the unknown-fault brake rather than relying on it, just using it to hold the trike stopped while at the traffic lights.

After my shift ended, I was able to examine the brake in detail in the coolness of the breakroom where I park the trike, and found the springclip piece welded to the rotor. I should have taken a picture of it before touching it, but I rubbed my fingernail across it and it came off, and I could not find it on the speckled tile floor. I thought I got pics of the rotor pads and rotor, but apparently did not so I'll have to go take some and edit them in here tomorrow.

Because I do only have the front brake, I carry a spare set of pads and spring clip with me; they're the "meh" Dymoece pads

Amazon.com

rather than the Avid originals (which is what were damaged), but they work almost as well, and are more than sufficient, even though they wear faster (and aren't copper backings like the Avid so presumably don't shed heat as well, which might be why they wear faster?).

It's only a minute to swap them out, and a few minutes adjusting the caliper pad knobs and brake lever cable adjuster, then it takes a couple dozen to a few dozen miles to wear in the new pads for best braking (they're about halfway into that process, I'd guess, but they're sufficient as-is).


I just don't know what caused the spring failure that allowed it to touch the rotor; it shouldn't be possible; the pads were still only about half worn thru. Maybe the pics of the remainder of the spring or the pads will help figure that out.


(this is crossposted to the SB Cruiser thread over here:
The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier )

 

[marvin78]

Hydraulics wouldn't have prevented this problem, which was a lockup of the rotor in the caliper apparently caused by a chunk of pad, so changing to them doesn't seem like it would make a difference here.

They wouldn't have prevented the pad breaking off, but now that he needs to replace the caliper anyway ( that doesn't look.. 'salvageable' )

I'm a big fan of mt200's and they are a known brand super reliable decent 2 pot brakes which are well worth their money imo. I would only go for the ZTE / Zoom's if you really need a 4 pot ( on the cheap ).

If he get's better brakes though, he should get a better fork to deal with the braking force.

If your rotor is not bent or otherwise damaged it can still be used with the new caliper. Otherwise I recommend a rotor with the most metal in it (the least holes, and the smallest holes) for the most braking surface / grip, in the largest diameter you can get for the fork you will use.

Less holes also mean less heat dissipation. Probably irrelevant for a gravel bike, unless you're racing Unbound on it ( .. there should be ebike races, different power output categories and all.. I would for sure watch this )

 

[amberwolf]

used to have ebike races on a kart track down in tucson south of here, i went a couple times and was kinda fun till i broke my ankle taking crazybike2 around a hairpin turn a little faster than it could actually handle.

see the old 2010-2011 spooky tooth cycles death race threads for info on those if you're interested.

 

[marvin78]

used to have ebike races on a kart track down in tucson south of here, i went a couple times and was kinda fun till i broke my ankle taking crazybike2 around a hairpin turn a little faster than it could actually handle.

see the old 2010-2011 spooky tooth cycles death race threads for info on those if you're interested.

This forums search function has it set out for me I swear! I'll find them, eventually. Probably after my dog get's a well deserved walk

*note though, as mtb rider the appeal of racing on a cart track is less as racing over gravel On the other hand I seen TheVeganCyclist ride a race of his on this 'new format' which used... part of cart track, and some off road sections. Then it suddenly looked very much highly technical ect.. was fun to watch still hope to see that format more often but sadly it hasn't come up in my feeds.

Around here, fat chance they would organize something like that

 

[raylo32]

Yikes... never heard of this before. I Have Avid BB7SL mech brakes on one bike. Ultegra hydros on another, and XT hydros on my MTB conversion. Never anything like this. Thank god. As Amberwolf noted, I don't believe the type of brake (hydro or mech) is a factor.

 

[amberwolf]

Got pics of the rotor and pads and spring clip up. Rest of the pics are over here:

The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier

Lately I've been having good results from Specialized brand innertubes. Do they make 20x2.5 thickwall tubes with a TR-6 threaded valve stem? Sorry, not sure. I got them from FLBS when I was suffering the "evil innertube syndrome." Happily they had the size I needed (26 x 1.75-2.4), decent price...

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[amberwolf]

This forums search function has it set out for me I swear! I'll find them, eventually. Probably after my dog get's a well deserved walk

JellyBeanThePerfectlyNormalSchmoo does her own walks (doggie door to the inner backyard), but she not infrequently comes to get me to come with her and take her out into the full backyard. In this weather that only lasts about two or three minutes before she slogs back to the house melting all the way (even at night), but she still has to go make sure it's all still there.

*note though, as mtb rider the appeal of racing on a cart track is less as racing over gravel On the other hand I seen TheVeganCyclist ride a race of his on this 'new format' which used... part of cart track, and some off road sections. Then it suddenly looked very much highly technical ect.. was fun to watch still hope to see that format more often but sadly it hasn't come up in my feeds.

Around here, fat chance they would organize something like that

In general, I have found that waiting for someone else to setup / do / organize / make / etc what I'd like to have / see happen / etc is typically an exercise in futility...if you want something done, ya gotta do it yourself (or at least get it started).


Here's some posts / threads with references to the races; there's plenty more in ohter threads

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[marvin78]

Diesel is only 7, he loves to go out... It's getting late here, I'll post a picture tomorrow.

He's actually American, in more then just breed ( one of his parents actually has an US kennel card.. sadly the breed isn't recognized here ).

I found some of the topics, and also video's on YouTube. Sadly, there was a lot of noise And I don't mean that nice humming and buzzing, but more like bored out little 50 to 80cc two stroke's with big carbs, open air filters and short exhausts.

*insert sad panda face*