Straightening a Bent Bicycle Brake Caliper

 Occasionally, brake calipers become bent. Calipers get bent a number of different ways: bicycle falls over, caliper is used when not sufficiently tightened, bicycle wheel turns and front caliper hits frame, etc.

In this case, I have a 1950s era Schwinn Approved Weinmann 810 front caliper. The upper horn of the caliper has become bent. I suspect this bend is the result of the front wheel being jarred or turning too much, such that the upper horn bashed into the down tube. Given the extreme durability of welded Schwinn frames and the fact that the brake caliper is aluminum, it is no surprise that it would be the caliper giving way in that case.

 

 But all is not lost - the caliper can be straightened. The work is not complicated, but you must still exercise care. 

Disassemble the caliper and put the piece in a vise. If you are worried about damaging a polished brake caliper, Wooden shims can help pad the vise jaws so as not to mar the piece. Otherwise, make sure the vise has a good grip on the piece, but don't gorilla the vise so as to crush. It helps to place the piece in a vise fairly close to the bend you wait to straighten. That way, you don't put an S-bend into the piece by pulling in the wrong spot.

The caliper is gently heated using a small propane torch. Even one of the small butane torches will do the trick. You're not melting anything or getting anything super hot - you just want to warm the metal a bit. It's not so much that this prevents cracking, but more that it makes the metal a little easier to bend. That way, you can be as gentle as possible getting the arm straight again.

 

A pair of channel lock pliers with a couple thin wooden shims helps bend the arm straight again. Go slowly and use just barely enough force to move the arm back into position. 

It's important that you do this process only once - you don't want to go too far and have to re-bend in the other direction. That weakens the piece.

Steel calipers tend to be more forgiving than aluminum ones, but both metals will punish you if get heavy-handed and end up having to bend and re-bend the piece. Aluminum tends to punish you for mistakes faster than steel, but you should be careful and go slowly with both types of metal.

While in the vise, you can also make any other adjustments you need - fore/aft arm angle, initial tow-in, etc. Final tweaks like fine toe-in adjustments, can be made on the bike in final assembly.

Once everything is straight, you can clean, polish, and rebuild your calipers.