Weinmann Brake Lever Fracture

HovR

Über Member
Location
Plymouth
Just swapped the original levers on my Peugeot for some Cane Creek SCR-5's (going for a modern build on a retro frame). Upon inspection of the original levers I found they had a reasonable size well developed fracture! I'd just done 50 very hilly miles on it last Sunday too!

IMG_20150127_103522.jpg

Any engineers out there know what might have been the cause of this? Never seen another lever fail like it before, no falls or crashes either!
 

biggs682

Smile a mile bike provider
Location
Northamptonshire
not good
 
Location
Loch side.
I assume these are standard drop-bar levers and that the lever - out of picture - makes a recurve? In other words, when you pull the lever, the crack closes, not opens?
Stress cracks start at one end and travel to the other end where it either causes the component to break or it self-arrests like in this case. Without seeing inside the crack and examining both possible start places up close, I can't say where it started. If you are going to trash them, open the crack up completely and look at it. It will have a colour gradient - the dullest being the oldest and the shiniest the latest. Nevertheless, it is in a strange place.
 
OP
OP
HovR

HovR

Über Member
Location
Plymouth
I assume these are standard drop-bar levers and that the lever - out of picture - makes a recurve? In other words, when you pull the lever, the crack closes, not opens?

Yep, that's all correct. Wouldn't want to ride with them now, so I might have to take a junior hacksaw to the other side and open it up at some point!
 

the snail

Guru
Location
Chippenham
That is a stress fracture in a really weird place. Any other photos?
Doesn't look that weird, looks to me that when the lever is stressed, the underside would tend to open up, so that the inside would be in compression and the outside in tension. the design leaves a weak point with stress risers in the area under high stress, so not really that surprising?
 

Gatters

Senior Member
Location
Right Here
Ooops
 
Location
Loch side.
Doesn't look that weird, looks to me that when the lever is stressed, the underside would tend to open up, so that the inside would be in compression and the outside in tension. the design leaves a weak point with stress risers in the area under high stress, so not really that surprising?
OK, so you're saying the crack started on the inside of the hole and travelled outwards? I think I see the stress riser. In photo 4, the holes seem to have corners.
 

Ed no-more-lemons

Über Member
Location
The Burbs
Similar issues, so put a new old one on the mounting then the replacement does the same thing. Can't remember where the fractures occurred as binned the levers immediately and on the second occasion dismantled/re-assembly the caliper arms. so hopefully now all good.

My concern now being how prone to metal fatigue old aluminium can become. I, to be blunt have not got a clue. Although it is certainly of interest and reminfs me of a documentary about catastrophic fusilage failure on some new airliner in the 1950's!
 
Location
Loch side.
Similar issues, so put a new old one on the mounting then the replacement does the same thing. Can't remember where the fractures occurred as binned the levers immediately and on the second occasion dismantled/re-assembly the caliper arms. so hopefully now all good.

My concern now being how prone to metal fatigue old aluminium can become. I, to be blunt have not got a clue. Although it is certainly of interest and reminfs me of a documentary about catastrophic fusilage failure on some new airliner in the 1950's!
Metals don't age but they do fatigue. Fatigue is only caused by repetitive strain. Whilst aluminium does have a lower fatigue limit than steel (which has no upper limit under certain conditions), you don't have to worry about this unless your ride is a large pressurized airplane with square windows.

The reason these levers failed is because the lack of engineers at the design stage. An unfortunately placed aperture in the lever caused a stress riser from where cracks can propagate.
 
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