Rear disc brake is awesome, front squeals constantly! Haaaalp!
 

The bike - my Bullitt cargo bike (no, no motor), Shimano M6000 brakes. I've aaaaalways had trouble with the front brake squealing. I've gone over all the basic maintenance items and I still end up with a horridly squealing front brake. The rear is so quiet and dutiful that its basically perfect. I suspect brake fluid might be dripping out of the brake on to the pads. Its this possible or common? I'm tempted to replace the front break with a better model but I think I'm too inexperienced to make the call.

Any suggestions? I'm pretty frustrated.

Welcome to disc brakes, they squeal. My front rotor with 105 brakes squealed so loud it was embarrassing. And before anyone mentions it, yes I properly bedded in the pads when the bike was new. I tried every tip and trick I could find on the internet and nothing worked. Some things, like cleaning the rotor with rubbing alcohol, made it even worse.

I was at the point where I was going to sell the bike and give up on discs when I had an idea to sand the rotor. I got a little piece of rough grit that came in a tube patch repair kit and lightly sanded them in a circular motion just enough to scuff them up. Boom, silence. They've been quiet ever since. Even in the rain they hardly make a peep.

The front brake does more work than the rear, and is mounted on a less rigid part of the bike. My front sounds and feels a little different than the rear, even with new rotors and pads. I spend more time and money maintaining the front.

If front and rear are same diameters, you can try swapping pads and rotors. If you suspect contamination, don't try new pads on a contaminated rotor or vice versa.

A brake fluid leak should be visible--you definitely want to rule that out with careful inspection at the caliper.

Check the headset adjustment, too. That probably won't cause a high pitch squeal though.

My front brake was squealing so loud I was about to purchase a new fork with cantilever mounts. It only did this going down a grade when everything got hot. Nothing worked until I purchase an ebike disk rotor.

Last night I installed a new rotor and cleaned the pads. This morning I inspected the pads and noticed oil on the backs. I wiped them off and rode around the block, breaking hard a number of times. It squealed a lot but maybe its just the break in period. Got off, inspected the pads - more oil on the back. Rotors have dark streaks where the pads made contact. I was a little awkward putting the pads back in and took them out before properly seating them - I noticed more oil on the back.

It definitely looks like mineral oil is leaking through the piston seals. What should I do?

Sounds like a new caliper may be required. Condolences...

Condolences? A new caliper is a joyous occasion unless it is already something super high end or has some really whacky routing.

What should I replace it with? I'm kind of tempted to go with a SRAM Code RSC after reading a few reviews. The price is kind of high but I can get over that. Need to figure out if I'd need to replace the line - its a cargo bike so its longer than standard length for a front and it would be switching from mineral oil to DOT.

I think I'd still try to figure out the front caliper - at this point I'm not sure if this is the second one to fail on me or if I have another brand new one in my basement. I could ride without a front brake for a bit....annoying but I already avoid using it due to the squeal.

sometime a disc is noisy and only changing it fixes it. like when I tried metallic pads on my magura mt4's they got wet right after I needed them in the squeal was horrible and they got a worble that I could not get rid of that took a new rotor and back to the old pads. but hone Got some xt 4 piston calipers those same rotors with metallic pads are nice and quiet and only a little noise in the rain.

New rotor and cleaning the pads is a bad idea. Pads are porous, if they're contaminated more than very slightly you cannot clean them. Given enough effort you can always get a rotor clean, though it's often not worth it. Sometimes Shimano brakes will leak from the backs of the pistons if the bike sits a long time without use

Clean the bejesus out of your new rotors, new pads, good adjust. If this is a recurring issue I recommend replacing the caliper. If you want more power you could switch to a Shimano 4 piston caliper, or just another servo wave compatible 2 piston. I honestly can't recommend any sram brakes—they're prone to master cylinder failure.

>Pads are porous, if they're contaminated more than very slightly you cannot clean them.

Seems like a recipe for throwing away a lot of pads if you're having a problem.

I must have some rotten luck with my front brake. I can't imagine many people have this into to disc brakes, nobody would find them worth the hassle.

Yes, just rotten luck. As long as you find the source of contamination and fix it appropriately, you'll end up with an excellent set of brakes that far out-perform rim brakes. Well-modulated and effective braking is worth the extra cost and weight for many.

If that front brake has always squealed, you've never had a properly working front brake. If you get it working, and re-learn how to do most of your braking with it, you'll be pleased with it.

My last bike had cantiliever brakes, and I fought those damn things for over twenty years, adjusting them carefully several times a year to minimize noise and maximize torque. When I finally got a disc brake bike, I had to learn a new set of maintenance skills and had a few problems with them (used bike came with a rotor deformed from brakes held hard on a hot rotor), and didn't like the cost of pad replacement, but in my first sleet storm with the bike it was all worthwhile.

Don't mix Shimano and SRAM brake components. SRAM uses DOT fluid, Shimano, mineral oil.

Squeal is caused by vibration, and vibration is caused by something that isn't properly tightened or aligned. Consider the headset, fork, front hub, and brake mounting points. If this checks out, try sandpapering the brake pads (off the bike) and re-centering the caliper (an off-center caliper can cause vibration). If this doesn't work, try Squeal-out. Squeal-out is a paste that's applied to the rotor and transferred to the pads through braking action, then wiped and washed off with denatured alcohol. If that doesn't work, try sprinkling some dry dust from the side of a road or driveway on the pads and rotor. Then ride as if you're bedding new pads and the rotor. If that doesn't work, consider a new Shimano brake.

It can be, but really most contamination is from mistakes during handling or maintenance. If there is leaking from the pistons the only solution is to replace the caliper (for Shimano at least, also warrantee-able if in warrantee period). As a working mechanic, it's definitely 90% people accidentally getting oils on the pads. I've never had a contaminated pad on a personal bike. I have seen legitimate issues with calipers that have caused contamination however. I've also totally made mistakes in the shop and contaminated a customer's brakes--free fresh pads and a nice clean rotor for them and a lot or wasted time and a likely unprofitable work ticket for us. Then again, I've bled many hundreds of brakes, has happened a couple times.

I've removed the brake from the bike and its now hanging from the ceiling in my basement. I've thoroughly cleaned the brake and the backs of the pads and let it sit for an hour. I found a small amount of mineral oil residue on the back of the pads. Its my guess that there will be a significant amount of residue by tomorrow morning. Once a rule out leaky pistons I can move on to pads and rotors. If the piston leaks then the brake gets replaced.

Its a heck of a lot easier to get a good view of everything when its NOT on the bike. It wouldn't matter as much if it was on a normal bike.

Here's what the back of the pads look like 12 hours after a very thorough cleaning - https://imgur.com/a/9WUZOvP

Forget about cleaning. Your caliper is shot. I just went through this same issue. Front brake would squeal, I'd take everything apart, sand rotors replace rotors, replace pads. Squeal would go away for a while and then come back only on the front. I didn't pay too much attention to it as I got used to using in lieu of a bell to alert pedestrians. Then my brake lever started bottoming out. I thought about bleeding and adding fluid but it didn't make sense that air in the lines would cause these problems. Turns out it's a common problem at least for shimano brakes for the calipers to leak.

Disc brakes work well in the winter in wet conditions but, at least in my experience, require significantly more maintenance. On other bikes I still have 20 yr old rim calipers that have done 10s of thousands of miles with zero issues or maintenance other than replacing pads.

No amount of cleaning can remove all contamination. Start over with new parts.

-SP

Update - I replaced the caliper, cleaned the disc, and I'm using new pads. No squealing!

I had another M6000 around which I installed. I asked my wife if I should just get a new caliper and she said no. I couldn't decide since I was so angry at the situation. I suspect the problem will come back eventually - maybe in a year or two? At which time I'll replace it with a high end caliper.

From now on, whenever that thing gets dirty I'm going to check the BACK of the pads for oil. Also, its MUCH easier to work on the brake when entirely removed from the cargo bike! Huge difference!

Of coarse you can clean pads, you just need a propane torch to do it. Heat them up to burn any contamination off, clean the rotor with brake cleaner and pop the pads back in after they cool down. Good as new. I've done it multiple times including a few hours ago on the back brakes on my road bike.

Is she looking to cash in your life insurance policy? Pad/rotor contamination from oil is no joke. The brakes will not only make a ton of noise, they eventually won't stop the bike very well. And, unfortunately, the calipers aren't able to be rebuilt. Some have mentioned cleaning the pads, and this works if the contamination is not severe and occurred from an external source to the brake system, but with a broken piston or piston seal, they'll just recontaminate. What I found odd though is that you stated there was visible oil contamination on the pads, but made no mention of reused braking pressure as felt at the lever. Regardless, you took the only viable route, in my experience, many of us have been there. Glad you got it sorted.