Introduction: Old Bicycle, New Wheels - Building a Drop Bolt to Make the Brakes Fit.
I have an old bicycle frame which I love, but it desperately needed some new wheels. Old frames like this use 27" wheels. Most replacement wheels aren't built to modern standards and the tire selection is just terrible. New wheels are smaller (700c) and are too short for most brakes to reach the rim properly. The solution is a set of drop bolts!
I first read about this on Sheldon Brown's website, but he doesn't show how to build them. This instructable fills that gap.
Please note - If you build them and your brakes fail, don't come after me. Your bike was built to use a certain size wheel with a certain size brake. Change these things at your own risk.
A note about wheel sizes: I am using a set of 26" mountain bike wheels on a frame designed for 27" road wheels. The long-reach brakes shown here will reach a set of 700c wheels from the stock mounting location, but I didn't have another "spare" set of 700c wheels lying around. I did, however, have a set of mountain bike wheels. This bike is primarily used for a trainer so I don't have to mess with taking my favorite road bike off the trainer every time I want to go for a ride in the real world. The smaller wheels drop the bottom bracket and increase the risk of striking a pedal on the ground during a turn. If you mount a set of smaller wheels, always be aware of this when making turns.
Step 1: Tools You Will Need
- Aluminum bar stock - I bought mine at the local hardware store for about $7. Don't go too narrow or too thin. It has to handle the force of stopping you!
- Bolts and lock nuts - be sure to measure the size of the bolt on your brakes and get the same size from the store.
- Aluminum tubing (not shown). It should be big enough to slide one of your bolts through and thick enough to handle the clamping force of the brake.
- A hacksaw (for cutting the bar stock)
- A drill and the right size drill bits (match it to the size of your bolts).
- A wrench or two.
- Some sandpaper or a file (not shown).
Step 2: How Low Should It Go?
This is the trickiest part of the process. You have to figure out how low your brakes should drop from the original mounting location for the brake pads to reach the rim. This will vary by frame, fork and brakes. It might be best to break out the measuring tape, but I chose to hold the brakes and the aluminum stock in approximate position and mark the bolt locations and cut lines with a pencil.
Step 3: Time to Cut and Drill
Mount the bar stock in a vice or get a really good grip and get after it with a hacksaw. Cut the bar stock to your estimated length. After you cut it, take it back to the bike and check the location for the first bolt hole you must drill.
Once you know exactly where you want the first hole, use a punch to create a starting point and then mount the stock back into the vice. The punch isn't necessary, but it helps to keep the drill bit from wandering when starting the hole.
Double-check the second hole location before drilling it. Once two holes are drilled, triple check the hole locations by mounting the drop bolt on the bike and sliding the brake into place. The brake pads should align with the rim. If the holes are spaced incorrectly, there will not be enough pad adjustment on the brakes to make them align with the rim. If that happens, start over.
Step 4: Cut and Drill the Second Drop Plate
Use the hacksaw to cut the first bar plate down to length, then use it as a template to make a second drop plate for the back of the fork. This is necessary to match the thickness of the fork. Without it, the brakes won't bolt on.
When you are finished, you should have two matching plates. These will have rough edges which need to be either filed or sanded down.
Step 5: Time to Bolt It All Together.
The brakes should have a couple of nuts which prevent the brake from rotating when tightened. Slide the first one on the brake bolt with the grooves pointed toward the brakes. Next, slide on the drop plate.
The next piece(s) to slide on are the spacer(s). It is probably best to cut a piece of aluminum tubing to the correct length, but a stack of washers or nuts will do. The only tubing I had on hand was too short, so I added a couple of nuts to fill in the gap. The idea is to make the stack long enough so the drop plates fit snugly against the fork.
After the spacers, slide on the second drop plate and the final anti-rotation washer with the grooves pointed toward the final nut. Place the final lock-nut and tighten, making sure everything is aligned.
Finally, slide the brake into position so the holes in the drop plates align with the brake mounting hole in the fork. Slide a bolt through and tighten with a lock nut.
Make sure the pads will reach the rim and align properly. Now install the brake cable and it is ready to go!