Rear brake makes a "thump" 1x per revolution
11-14-10, 10:20 PM
#1
Newbie
Thread Starter
Join Date: Aug 2010
Posts: 3
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Rear brake makes a "thump" 1x per revolution
So I got this new wheel. When braking if the rim is cold it seems fine.
If I'm on a descent and using the brake after some time (100ft+) of braking, I start feeling this "thump" every time the wheel goes around. I assume the rim is heating up, and causing some deformation, does that sound correct? It's sort of hard to find since on the work stand it seems perfectly smooth.
Any ideas?
-john
If I'm on a descent and using the brake after some time (100ft+) of braking, I start feeling this "thump" every time the wheel goes around. I assume the rim is heating up, and causing some deformation, does that sound correct? It's sort of hard to find since on the work stand it seems perfectly smooth.
Any ideas?
-john
11-15-10, 02:41 PM
#3
Senior Member
Join Date: Oct 2004
Location: NYC
Posts: 2,124
Bikes: All 70s and 80s, only steel.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 2 Times
in
2 Posts
Make sure the pads are low enough to be ONLY in contact with the rim--if one is impinging some very small amount on the tire, a warmer tire could be bulging out just enough and touching the rim for you to be feeling it. As Kwoodbury mentioned above, check both surfaces of the rim. Try running your finger over the surfaces, and also, shine a light down from above; look to see if the rim isn't reflecting light back with the same shine in some spot.
11-15-10, 03:23 PM
#4
Senior Member
Join Date: Feb 2005
Location: Oklahoma
Posts: 9,438
Bikes: Trek 5500, Colnago C-50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 7 Times
in
6 Posts
This sort of thump is often associated with the rim joint, sometimes cured with a flat file.
11-15-10, 03:43 PM
#5
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,716
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5788 Post(s)
Liked 2,580 Times
in
1,430 Posts
You'll also probably see some rubber transfer on one side or the other of whatever is causing the thump. Look for the Telltale black (or salmon) transfer and feel that area for any distortion.
You might also wait until it happens, then get off the bike and spin the wheel with the brakes closed just enough to work as feeler gauges, and possibly see the exact cause.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
