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Old 06-28-08, 06:53 AM   #1
Equinox
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How Do Mechanics Diagnose Bike Noises?

My bike has about 10,000mi. on it and has been lovingly cared for. It has always been a real quiet runner so any noise is noticeable. I'm not smart enough to figure out where the noise is coming from, but it does cause me concern because it is so unusual for my bike. Initially, I thought it was from the drive train. When they put it on the stand and ran it through the gears, it was perfect. When I was riding last night, my bike was making a clicking sound when under load, like climbing a hill in a harder gear. It was fine when I was spinning on a flat surface. How does a mechanic duplicate a bike under load when he has it on a stand? Or is it even necessary? Are they able to detect a problem without duplicating the exact conditions at which the problem occurs? I guess my concern is that I'm developing a problem with my bottom bracket. How many miles can you get out of a bottom bracket?
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Old 06-28-08, 07:18 AM   #2
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I test ride the bikes I am working on to test them under load and afterwards to make sure they function properly under load.

BB mileage will vary... my last one went 7000 km.

It sounds like the bb or pedals might need some attention although it could be something as simple as your chain ring bolts needing some torquing up but if that BB has gone 10,000 miles it is probably due to be replaced as I would almost bet that is the problem.
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Old 06-28-08, 07:40 AM   #3
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I had a noise that I couldn't trace easily because it only happened under load. Turned out to be the bottom bracket.
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Old 06-28-08, 07:54 AM   #4
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99% of the time it trial/error based on experience.

I start with the usual suspects, grease and tighten.
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Old 06-28-08, 08:06 AM   #5
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its come from years of experience .
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Old 06-28-08, 09:03 AM   #6
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You could bring a long dowel rod on the ride with you and get it to start making the noise and put the dowel
up to your ear and place the other end on various components until you find where it is the loudest.
You could probably even hear the noise using this method with a screwdriver while it is on the stand since
it will amplify the noises. Auto mechanics have stethoscopes made just for this but they have a long metal
rod connected to it for diagnosing motor noises, But a long screwdriver or wooden dowel rod works just as
well!!
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Old 06-28-08, 09:50 AM   #7
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When it comes to phantom noise I generally start checking anything that could be moving in the drive chain and making sure all fasteners are at the proper torque spec. Sometimes a creak is something as stupid as a loose chain ring bolt. Start with all the little, simple stuff and then move on to the bigger problems.
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Old 06-28-08, 12:51 PM   #8
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Does the sound occur at the same frequency as your pedal-strokes? Like once every pedal revolution? Usually those are BB/crank/pedal related. Simplest is to re-torque your crankarm-bolts. Loosen slightly and tighten up to 30-35 lb*ft with torque-wrench (use manufacturer's specs).

BB cups tend to be loose in the threads. While locking it laterally with torque works to keep it from loosening, it does nothing for vertical displacement. The cups can actually move up and down in the shell slightly. This can occur after a year or so as the grease used during the assembly dries out and leaves gaps in the threads that can allow movement. I usually use teflon plumbing-tape to install the BB cups. It serves an anti-seize function as well as fill up the gap between the threads to prevent movement and noise.

Pedals are notorious for noise. The loose fit with the cleat can allow movement and noises. Loose cleat bolts can allow movement of the cleat and rubbing on the shoe can cause noises.
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Old 06-28-08, 03:01 PM   #9
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Quote:
Originally Posted by dobber View Post
99% of the time it trial/error based on experience.

I start with the usual suspects, grease and tighten.
+1. It's often tough to pinpoint, since the frame could transmit noise. What sounds like the bottom bracket could the headset. I had what I swore was a creaking bar/stem interface. After many tries at adjusting/tightening, it turned out to be the seatpost.

The best way to gain experience is to vary or work on one component at a time until the noise goes away. If you do three or four things at once and the noise goes away, you really won't know the actual cause. It takes a little patience and detective work.
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Old 06-28-08, 03:19 PM   #10
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How does noise originate from the seat post? I did adjust my saddle height just before the noise started.
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Old 06-28-08, 03:29 PM   #11
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How does noise originate from the seat post? I did adjust my saddle height just before the noise started.
It's funny that you ask.....

Recently I notice that my usually very trusty single speed was making a creaking noise. I could only make it happen when I got up out of the saddle and torqued on the frame. This had me extremely worried with thoughts of failing brazed joints running through my mind.

I stopped by my local LBS where I'm a regular fixture and we put it on the stand and I got one of the guys to flex the frame while I looked for the source. In an attempt to feel if it was a joint I removed the seat post and VOILA! Noise is gone.....

Seems that the trustly SS had been SO trusty that the grease I used on the seatpost had finally been washed away from a few years of our typical rainy winters. The post came out with only a little grease on it along with some rust from the frame tube.

Next on the list is a bucket of frame saver and some time spend on preventative sloshing on this as well as my other couple of steel frames.

It's truly amazing how much our bike frames can flex in use. Almost anything attached to it can be the source of a creak if it's dry. ESPECIALLY a seat post that overlaps so much of the seat tube.
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Old 06-28-08, 05:20 PM   #12
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I worked as a bike wrench for a year. For me, it was a lot of poking and prodding. For the head mechanic, it was some sort of voodoo magic.
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Old 06-28-08, 05:45 PM   #13
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Sometimes they can't.


And sometimes they employ the shotgun approach we fear from all mechancs: replace everything in the area until the problem goes away.
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Old 06-28-08, 09:39 PM   #14
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Sometimes they can't.


And sometimes they employ the shotgun approach we fear from all mechancs: replace everything in the area until the problem goes away.

That happens when the customer cannot even provide a basic explanation of when and how the noise occurs.

The deal is there are a few culprits in the mysterious noise game. Nine times out of ten the customer cannot even tell you the circumstances under which the sound occurs(or what gears the bike skips in, etc) This leaves the mechanic to guess at the problem, much like when you go the library and ask for a book with a story about a guy that visits Europe, the pro has near nothing to go on and just starts handing you books.
Fortunately, with bikes there are a limited number of things that can cause a noise, and they pretty much all just need to be tightened, lubed, or both. So the shotgun BS above is more or less moot. It is not parts that are being replaced, but items being serviced. Which, if you have a creaky piece of junk, probably could stand looking at anyway.
In conclusion, you need a shotgun when the customer gives you no fixed target. If your bike makes a noise spend a few minutes figuring out when it makes the noise, then you can provide the mechanic with some useful information that will decrease the diagnosis time. If you can't be bothered to make this effort to solve your noise issue, STFU when you get a bill for an hour plus of repair time becuase the mechanic had to check every nut and bolt on the bike to find the creak.
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Old 07-07-08, 07:57 PM   #15
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File under "if it ain't broke ,don't fix it".
Tonight I took my chain off to clean. Took rear wheel off to clean cassette. I didn't have anything else so I used gasoline. Cleaned up real quick. I removed chain ring bolts to get a good clean on the teeth. Put everything back together, chain lubed, everything lubed. Got on to ride home, my once ultra quiet ride now has a phantom noise. Under load only, NOW have a rhythmic tic but sounds more like a toook and occasionally it has a duplicity like two strings have been hit on a guitar(but a double tooook) not one. It sounds like a shoe lace is hitting the spoke or something dangling must be hitting the wheel. Get off the bike and can't duplicate it. Driving me nuts. This will happen under load while coasting, no cranking necessary, but also happens while cranking. The speed of noise doesn't seem to keep up with the speed of revolutions but does increase with speed.
Any guesses? Up till tonight this bike was silent.
Sorry to tag onto this thread but it came up in my search..
thanks in advance.
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