Ask a Mechanic: Squeaky Disc Brakes and Bolt Grease

This is the sixth edition of a column we’re running here at Art’s Cyclery where our expert mechanic Daniel Slusser answers your bike maintenance questions.

If you have a question for Daniel, please post it on our Facebook Wallor e-mail Daniel directly at daniel.slusser@artscyclery.com.

Question: My new XTR disc brakes are really howling. They seem to get worse at the end of a long descent. It’s really annoying. How do I fix it?    From: Sam

Sounds like your brakes are trying to tell you something. Howling new brakes are usually the result of either improper break in procedure or pad/rotor contamination. Either way, you will need new pads. Anytime you have new pads, rotors or both, a specific break-in procedure needs to be followed.

First, clean the rotor with rubbing alcohol and a clean rag. Make sure the new pads are free of oils and waxes. This means that you should never touch the braking surface of your rotors or pads! Anytime you get oil on your brake pads they need to be replaced. There are ways to mitigate contamination issues, but once pads are contaminated they are never the same afterward, so there is no use in reviewing these methods.

After getting everything installed, make several controlled stops on level ground or a slight downhill section of pavement. These stops should be initiated from a speed of 15mph or less. You don’t want to come to a complete stop however, just slow to about 2mph (walking speed) and repeat the process until brake power and consistency improve. Be sure to break in each brake separately so you can be sure that one isn’t compensating for the other. Don’t try to speed up the process by going down a big hill and trying to do this all in one shot. This will create the problem you are trying to avoid and glaze your pads making them chatter against the rotor.

One last thing that I like to do to help avoid noise problems is to chamfer the leading and trailing edges of the brake pad friction material on the grinder. This will help smooth pad contact with the rotor and cut down on noise.

Finally, pad material choice will have an impact on the noise issue as well. Organic pads tend to run quieter but are more easily damaged by high heat. So if you are a downhill ripper, chronic brake dragger or if you ride long, steep trails, then sintered or metallic pads are a better choice. They will be noisier under normal conditions, but it is nothing that can’t be handled by a rider with good mental health.

In the worst-case scenario that you can’t fix the noise, just think of your brakes as a horn to warn other trail users that you are headed their way. To borrow and modify a line from the Harley riding community, “Loud brakes save lives!”

Question: I’ve noticed that most of the bolts on my bike have grease applied to them but others have Loctite? Which parts require one or the other?    From: Matt

Park PPL-1 Polylube 1000 Grease 4oz Tube

Park Polylube is a great all-purpose grease for use on metal-to-metal interfaces.

To grease, or not to grease? This is a valid and thoughtful question. The reason bicycle bolts are generally greased is to prevent seizing. Dissimilar metals have a tendency to corrode when in contact with each other. Most bolts on bicycles are steel and most components are aluminum. Even if you have a steel bolt in a steel frame, grease will help keep rust at bay by keeping out water and treating the metal at the same time. In addition to its anti-corrosive properties, grease helps lubricate the threads for easier turning and protects aluminum components with cut threads from stripping.Lastly, this lubrication prevents bolts from backing out. This is somewhat counterintuitive, but works because dry bolts have a tendency to “ratchet” themselves out of nuts that they aren’t seized to.

When working with titanium, anti-seize is a good choice as it provides greater protection against dissimilar metals bonding themselves to it. This mostly applies to titanium frames. Modern titanium bolts don’t seem to have these corrosion problems, however, and I have never had a seizing issue when using grease on them.

So which parts get Loctite? This is generally reserved for brake bolts, chainring bolts, and suspension pivot bolts. Just make sure that the metal is clean and free of grease or else the Loctite won’t hold. Also be sure to use the blue formula, which is non-permanent. I prefer the version that comes in a stick rather than a liquid, as it is easier to apply and stays put while I install the part.

My favorite alternative to Loctite is plumber’s Teflon tape. Just wrap the tape 3-4 times around the threads in a direction that will tighten the tape as the bolt is tightened. The tape functions like the nylon inserts in locking nuts, only in this case, the nylon is applied to the bolt. Plumber’s tape locks out water just like the other thread prep alternatives, but doesn’t act like glue that has to be broken in order to remove the bolt.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2015-03-20T13:05:19-08:00