Bicycle Mechanics - please help me with this brake system (drum brakes?)

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nikolozj
09-29-12, 07:26 AM
My mom got this bike for herself, it's really old and it's really really heavy bike...
There are several things I need to fix on this bike and one of the first things is brakes!

I've never fixed this kind of breaks. The main problems it has is:
1) back brake even on very light touch brakes very tightly and it just freezes the wheel and you may even jump forward a little
2) front brake has a terrible noise that will blow your brains out

I took apart only back brake and found this mechanism, that looks like car's brakes for me...
the material that is used to rub against metal, seems to be fine and still a lot...


http://i48.tinypic.com/2cptgg7.jpg

http://i47.tinypic.com/23t4m6e.jpg

http://i49.tinypic.com/sg7rzt.jpg

what would help?

oil?

rhenning
09-29-12, 07:30 AM
If it is locking the wheel I suspect the drum is bent or warped. Roger
nikolozj
09-29-12, 08:07 AM
could it be such a little bent that one wouldn't notice visually?

this is exactly that brake opened:

http://i48.tinypic.com/2cptgg7.jpg

Airburst
09-29-12, 12:54 PM
could it be such a little bent that one wouldn't notice visually?




Quite possibly. It wouldn't take much.
FBinNY
09-29-12, 02:27 PM
Test the brake for modulation off the bike, by applying very lightly and hand turning the wheel to feel if the drag is uniform, or has a place where it is noticeably tighter. If there is clear pulsing, with tight and loose areas as the wheel turns, that would confirm a warped drum. If the warpage is very slight it may self correct with wear, but if it's severe the brake is toast. In theory you could turn the drum (as is done for cars) but there isn't enough material for this solution on most bicycle drum brakes.
Airburst
09-29-12, 07:11 PM
I'd also add that severely imbalanced spoke tension could be warping the hub shell, and therefore the brake drum as well. Check the spoke tension by plucking the spokes like you would a guitar string - if some of them produce wildly different notes, the tensions are uneven, which could be the issue.
speedy25
09-30-12, 10:41 AM
remove the shoes and make sure the shaft for the brake cam turns freely. They typically seize and cause wacky brake problems. After you get that done reassemble the shoes witha very light amount of grease on the pads that contact the cam.

The style of brakes are VERY common on motorcycles so I have had a lot of experience with them over the years.

-SP