Saturday, August 24, 2013

Straightening Bent Levers.

So you dropped the bike?
And the levers took the hit. Well, as long as they aren't snapped clean off, you might be able to save them. 
I'm concentrating on aluminium brake, clutch and gear levers for this post (I'll mention steel at the end).

Aluminium (Al) is light, corrosion-resistant, and can easily be cut, drilled, machined, polished etc. It can also be worked (bent or shaped) relatively easily if you treat it the right way. But it will work-harden, which means the more you bend it, the harder, and more prone to cracking, it becomes. Hence why they normally snap in a spill.

Why can't I just bend it back?
Hey, you might be lucky. A slight bend may go back easily enough, but I don't recommend trying it without annealing the part first. And it's such a simple process, you'll be glad you spent the time doing it properly.

1) Blow lamp
2) Soap, yes really.

If you've ever needed to bend steel, using heat, you'll know it needs to be cherry-red to allow it to move easily. But you don't have that luxury with aluminium; it won't change colour, and excessive heat will just melt it (660.3˚C). Which is where the soap comes in... so, without further ado.

Grab your levers!

1) Here's the brake lever off the trusty old GS425 rolling chassis project (which hasn't yet been started). Heavily corroded, but ideal for this test. Aluminium not only gets harder with bending, but age too, so this should be a cool experiment.
First I traced around the lever on a piece of cardboard. It's easier to work out how much of a bend you need, and how far to go if you have a template.

2) Sorted. I have no idea if that's the original factory shape, but it looks far too straight for me.

3) It's a piece of soap, or is that cake, no it's a bar. Well, whatever it is, any old soap will do.

4) Rub the soap on the lever in the area you want to bend, but keep it on the opposite side of where you'll be heating. You want the heat to conduct through the aluminium and react with the soap.

5) I've mounted the lever between two bits of wood in the vice to prevent scratching, and to stop the vice acting as a heat sink.

6) After a few goes back and forth, you'll be left with these fine grains of soap.

7) Light the blow lamp and run it back and forth underneath the lever until you see a change in the soap. 

8) It'll turn black when the lever is hot enough.

9) Any doubts? Rub the soap back over the lever and it'll discolour instantly if the lever is hot enough.

10) Perfect.

11) Will that lever now bend easily? I'll bet on it!

12) Now grab some thick gloves (if you like the use of your hands), or just allow it to cool by itself, then mount it in the vice so you can pull on the lever. Use rag to protect the lever if you're concerned about scratching (I'm not).

13) I'm just using a piece of box section tube that was lying on the floor. Start as close to the pivot as possible and give it a gentle pull. 

14) Go easy! It's still a fragile lever, and you should move along slightly before another gentle bend.

15) Don't be greedy. To give a smooth curve, you need to take it one little section at a time. Any doubts, place it on your template for an idea of where it needs to be bent next.

16) It's clear to see the difference. This is great if you have a large handspan and your levers aren't adjustable.

17) A scotch pad will soon remove the old soap, leaving it ready for a polish.

18) Yes, I know this lever is heavily corroded, but it lives to fight another day.

Don't be too quick to throw them away!
It took five minutes to get a nice smooth bend in this lever. Annealing softens the metal and allows it to be worked. Over time it will get as hard as it was before.

Steel brake and gear levers on modern bikes are usually thin and soft enough to bend back into shape without heat. And yes, I've found this out on the road after dropping  the odd bike or two. 
Cast iron brake pedals, from years past, are better adjusted when heated cherry-red. Cast iron cracks easily when bent! (I know this too:) 

Hope that helps someone!