Aligning a Bent Derailleur Hanger

 In the past, I would carefully bend rear derailleur hangers back into shape with an adjustable wrench. There is a more precise method of re-aligning them, however. The threads inside a derailleur hanger are M10x1.0. A rear wheel with a quick-release axle also has M10x1.0 threads. You can use another rear wheel to precisely align a bent derailleur hanger.

 First unbolt the rear derailleur:

 

 

Next, screw the axle from your spare wheel into the hanger, and tighten it in place with a wrench:

 

 

Now you can measure the distance between the two wheels in all directions (top, bottom, left, and right). 

 Compare these measurements, and bend the hanger back into shape using the wheel as leverage. When the measurements are the same all around (or at least very close), then you can reinstall the rear derailleur. I would also check the limit screw adjustments to make sure it doesn't over-shift, since the derailleur will be in a new position.

Fork Alignment

 Sometimes I come across a bike that doesn't track straight. If I try to ride with no hands, the bike will veer off in one direction. This is usually caused by a misaligned fork. I made a simple tool to check the alignment of the fork blades:

 

 This was an old curtain rod that I crushed flat in a vise. The round end goes into the steerer tube, and the flat end sits between the fork legs. The cross bar fits across the fork to hold tension on the tool and keep it in place while you measure. These two pieces are loosely bolted together with an M5 nut and bolt. You could also make something similar with two pieces of 3/4" by 1/16" steel or aluminum flat bar stock.

To use it, first unbolt the front brake and slide it out of the way:

  

Then, insert the tool into the steerer tube, and rotate the cross bar so it sits across the fork legs. The spring pressure from the backward bend in the middle bar will keep it centered in the steerer tube: 

 

 Now you can measure and compare the two sides:

     

This fork is misaligned by 1/8" of an inch. That was enough to affect the bike's handling. If your fork is steel, you can carefully bend it back into alignment by pulling or pushing on the fork legs while bracing the head tube with your foot. If it isn't steel, then you'll need a new fork.

Saddle Top Repair

 The original saddle from my Miyata 100 was peeling away from the foam underneath. This can be fixed by spraying contact adhesive in the gap between the two layers:

  

 After waiting a few minutes for the adhesive to become tacky, I could pull the top cover tightly over the foam and press it back into place. I then wrapped the saddle up with an inner tube overnight to make sure it was secure:

 The repair came out well, and the top was no longer peeling away from the base: