Bottom bracket knocking, no help from LBS
08-16-14, 09:22 AM
#1
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Thread Starter
Bottom bracket knocking, no help from LBS
OK, I took my bike in for a tune up for the first time ever last week, the bike is 23 years old and has maybe 3000 miles total on it, I bought it in 1991, rode it intermittently for a couple of summers then it hung upside down in several garages over the last 20 years. I got the bug again and have put about 2000 miles on it in the last year. I'm pretty good at fixing things so I've taken care of the brakes, tires & chain myself, but took it to the LBS for the things I'm not confident I can do. Specifically check & lube the bearings, true the wheels, adjust the indexing on the rear end, and I wanted them to check the bottom bracket for a ticking or knocking noise. I got it back, went out for a short ride this morning and the knocking noise is still there. They charged me for a bottom bracket overhaul, but there was nothing said as to anything they found. And this is probably nitpicking but they also adjusted my front brakes, now they squeal and aren't centered...
As to the knocking noise, it happens only under load, and only in fifth through seventh gear (I'm usually on the middle gear up front). If the bike is in a repair stand it doesn't do it, only when I'm riding it. It knocks approximately three times per revolution, it stops when I stop pedaling. It usually starts up again when I start pedaling again, but sometimes it doesn't. If I pedal faster the knocking speeds up, pretty much keeping right at three knocks per revolution. If it is just bearings wearing out I'm alright with that, it can be replaced. What I'm worried about is something locking up at 20 mph and causing me to crash, and the noise bothers me, other then the knocking the bike is pretty much silent, I like it that way. The bike is a 1991 GT Arette 21 speed, any Ideas on what it could be?
And yes I'm taking it back to the LBS.
As to the knocking noise, it happens only under load, and only in fifth through seventh gear (I'm usually on the middle gear up front). If the bike is in a repair stand it doesn't do it, only when I'm riding it. It knocks approximately three times per revolution, it stops when I stop pedaling. It usually starts up again when I start pedaling again, but sometimes it doesn't. If I pedal faster the knocking speeds up, pretty much keeping right at three knocks per revolution. If it is just bearings wearing out I'm alright with that, it can be replaced. What I'm worried about is something locking up at 20 mph and causing me to crash, and the noise bothers me, other then the knocking the bike is pretty much silent, I like it that way. The bike is a 1991 GT Arette 21 speed, any Ideas on what it could be?
And yes I'm taking it back to the LBS.
08-16-14, 09:31 AM
#2
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"Three knocks per revolution" leads me to think it isn't the crank or bottom bracket. I'd be looking for something related to the rear wheel.
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08-16-14, 09:38 AM
#3
Senior Member
Retro Grouch is wise. Once or twice per revolution, maybe the BB area. Three times? Probably one of the wheels. Might even be your seat bag. Does it swing pretty freely or have anything loose in it.
08-16-14, 10:11 AM
#4
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No seat bag on the bike, as for the wheel, if it is the wheel, why would the knock stop when I stop pedaling? And it does sound like it is coming from the bb.
08-16-14, 10:16 AM
#5
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You need a new cassette and chain. That's the cause of the knocking.
The problems with the brake at not nit-picky. Fix them or get them to correct them.
I don't think it's their fault that they didn't find the knocking. These things are tricky.
The problems with the brake at not nit-picky. Fix them or get them to correct them.
I don't think it's their fault that they didn't find the knocking. These things are tricky.
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08-16-14, 10:42 AM
#6
Really Old Senior Member
Can't find any specs for that except it appears to have a 42T middle ring.
Divide 42 by the number of teeth of the cogs it knocks on.
Does that equal the number of knocks per crank revolution?
Divide 42 by the number of teeth of the cogs it knocks on.
Does that equal the number of knocks per crank revolution?
08-16-14, 11:48 AM
#7
Junior Member
Thread Starter
Middle gear on front is 42, rear is 13 to 30, I'll ride tomorrow and see if it knocks differently in 5th, 6th & 7th gear. Chain is new, it did this before and after installing new chain.
08-16-14, 12:25 PM
#8
Really Old Senior Member
Likely, your 3 smallest cogs are 13, 15 & 17,
So, 42 divided by those equals-
3.23
2,80
2.47
knocks per revolution.
See a trend?
So, 42 divided by those equals-
3.23
2,80
2.47
knocks per revolution.
See a trend?
08-16-14, 01:09 PM
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A lot of bike shops, in my experience, hire young guys who 'like bikes' for after school and weekend labor. The shop should give a rundown on what was found and fixed and the customer should probably do a little test ride before loading it into the truck.
08-16-14, 02:00 PM
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I wonder if this bike has a Sun Tour freewheel on it. They are known for sometimes developing a rocking on the two ratchet pawls when in the higher gears. Andy.
08-16-14, 03:06 PM
#11
Senior Member
Check the pedal , the knocking can come from one of them.
08-16-14, 04:11 PM
#12
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Change the cassette or freewheel, whichever you have.
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“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author
Please email me rather than PM'ing me. Thanks.
Tom Reingold, tom@noglider.com
New York City and High Falls, NY
Blogs: The Experienced Cyclist; noglider's ride blog
“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author
Please email me rather than PM'ing me. Thanks.
08-18-14, 05:48 AM
#13
Junior Member
Thread Starter
Went on my Sunday ride, on the big sprocket (52 tooth) & highest rear gear (13) I get exactly four knocks per revolution, 52/13=4...
So, can I do a drop in replacement of a Suntour accushift freewheel with an accushift plus or accushift 2 freewheel. I see AP+ and AP2 all the time on eBay, not so much with just the accushift.
So, can I do a drop in replacement of a Suntour accushift freewheel with an accushift plus or accushift 2 freewheel. I see AP+ and AP2 all the time on eBay, not so much with just the accushift.
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