Help: Brake bending
 

Hi,
My front campy SR brake is bent after a crash. The right arm is not parallele to the rim, about 20 degree angle. I need to bent it back. Do I need to heat it up? Or I just need to clamp it on a vise hit it gently with hammer?
Thanks

Alloy bits don't much care for being bent...then bent back...they tend to SNAP....You may be able to gently bend it back into place, but I am afraid it is STRESSED and may fail at a VERY bad time.....when you need it most.

Aluminum can take a bit of bending (judging from me surviving all those years bending caliper arm ends with a small adjustable wrench on my Weinmann calipers in the 80' to adjust pad toe-in.) as long as you are careful to asses the situation and make a proper decision whether to bother fixing the caliper arm. I think it really depends on the bend. If it is a sharp, short bend that you are trying to straighten out, the more likely you can end up cracking the brake caliper arm. But if is a more of a gradual arc along a longish legnth of the caliper arm, then it could be safe enough to carefully bend it back straight. But, of course, in all cases, you would be doing it at your own risk as the brake caliper is such a critical safety component on all bikes....
If you do proceed with the repair, just make sure you minimize the amount of bending to just once in one direction...as in not going to far one way and bending it back the other way, as each time you bend the arm you can be adding in more and more micro cracks in the aluminum material that could eventually develop into bigger cracks later and the caliper arm can the fail catastrophically at the worst time.....

Any pics? I think the location and shaprness of the bend are key. While I agree most alloys don't like being worked I think a brake may be soft enough to take a gentle amount of pressure.

How is the rest of the bike?

Thanks all for your advices. The bike is OK. Only pain scratch where the brake arm hit the downtube (thanks to the tiny rubber ring of cable adjuster).
I can't see the bend on the arm itself. only the space between rim and brake pad indicate there is a change in aligment between brake bolt hole and brake pad end.
I just don't know if the heat would help or necessary to stabilized the bent.
I we worry too much about safety then we should not buy any used bike and that not the case for us CVer!!!

I wouldn't use a bent (then bent back) aluminum alloy brake caliper. Especially not a vintage one.

Can't say it any better than Chombi did, but...it sounds like it may be just the part of the caliper arm that holds the brake shoe might be tweaked out a bit. If so, you can probably save it. Take the brake apart, hold affected arm in a vise with padded jaws, if available, and tweak the slotted pad holder portion back to straight with the jaws of an 8 or 10 inch adjustable wrench tightly clamped to the flats on the arm. The trick will be going exactly the amount and direction you need. Like Chombi sez, one bend is, ideally, all you get, and good advance planning will help a lot. No heat. Doesn't help much with forged aluminum. Good luck. Worth trying. You might even be able to accomplish it with the caliper still mounted to the bike.

Thanks. I worry that bending when it still mount to the bike only bend the brake bolt.

Are the front and rear arms interchangeable on these? If so I would consider swapping them. If a brake arm fails I'd much rather it be the back brake.

+1.........

In about 1981, I was in a crash at a race and bent the arm of my front NR caliper quite a bit. More than yours from your description. The good folks at RRB cycles bent it back without heat. It is still in service. I think you can bend yours back and safely get another 30 or so years out of it.

Yeah, I thought of that too. Plus, you'd have to hold the fork and wheel between your legs, etc. And with the wheel in place you may not have enough room for the movement of the wrench. The trick with it off the bike, disassembled, will be knowing how far to go and in which direction.

If it's just the lower part that bent (where the shoe attaches) you could put on a triangular shim to adjust the shoe.

take it apart, put it in the vise, bend it back, if it survives use it.
heat is not effective on alloy parts for bending.

When the brake was made, the only method there was for setting toe in was bending of the arms. Park made a tool for that purpose.

If the arm is really bent 20 degrees, I don't think I would trust it after bending it back. I'd look for a replacement on Ebay.

I haven't bent a high end caliper but I've bent many Weinmann and MAFAC's. They never broke. You haven't got much to lose by trying. Switching front and rear sounds smart.

Still no pics?

This should be ok for most calipers. Just don't try it with Universal calipers, though. :notamused:

Yeah, switching front and rear, after straightening is a really smart idea.

The Weinmann and Mafac brake callipers were 6000 series aluminum and the Campy brake callipers were 2000 series so the effect from heating and also re-bending is very different. The 2000 series aluminum can be heated to its solution temperature, re-bent and then, if quenched, it will naturally precipitation age within hours and after just a few days it is something like 90% aged. If you do this with 6000 series alloys, it takes a year to reach something like 75%.

Still, I wouldn't do any of these. Bent brakes should be replaced!

Pip

I took of the arm and hit hard with hammer but it doesn't do anything. Finally I was able to bent back the brake a bit by doing it while mounting on the bike. The bent may occure partly in the brake bolt itself. Now the angle is about 2mm different between 2 ends of the pad. I thought of the shim but then decide to let the wearing correct the angle. Switch front to back is definitively good advice, i will do that.
BTW, I put on the new red Kool Stop pad and the brake is smoother but squeal terribly. The old hard dry campy pad was quiet. What shoud I do?

There is a similar post/question in a current post (new salmon brake pads squealing; needs toe in); http://www.bikeforums.net/showthread...NR-Caliper-Arm I responded with this;

After bending the brake arms with limited success, I tried and succeeded with a very thin washer cut in half and mounted under the rear of the brake shoe, against the mounting bolt (to make this easier coat the washer with some sticky grease so it will stay put). Pads are perfectly toed in with no bending, grinding or sanding.

I find it hard to believe that anyone needs to be told not to hit it with a hammer! Use an adjustable wrench and bend slowly and carefully. I put tape on the jaws to prevent marring of the brake. Someone who hits brakes with a hammer obviously isn't concerned about marring them.

^ Same thing I thought. A hammer is one of the tools I would never use for this. Sure, it was bent in a crash, but trying to reverse the crash force/speed is one of the best ways to have you searching for a new arm to replace the now-broken one.

I did try first holding the arm in vice with padding and bend it with a wrench, not working. Then I tried to hit it with hammer using a piece of wood as cushion. Finally I used hammer to hit it directly in the back of the arm, nothing happen. The marring is minimal and can be clean with sand paper. Obviously this brake is made out from good material.

Except that they are nicely anodized... which sandpaper will destroy. Since you didn't post pics so that we could see the extent of the damage to the arm, kinda hard to advise.