Old Bicycle, New Wheels - Building a Drop Bolt to Make the Brakes Fit.





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

Below is a list of parts and 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).
Since I had most of the parts lying around, the only real cost was the new bar stock - about $5.

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!

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    Thanks! You just salvaged my favorite frame!

    use kerosene for lubricating and to prevent clogging of the hacksaw teeth

    2 replies

    TB-one can use ANY oil,no flames !,but oil the blade and material to be cut first,then add oil while cutting...

    This is a great idea! I was thinking of doing something opposite that- 700cc rims on mountain frame. Thoughts?

    9 replies

    i have already done something like this! I took an old huffy dual-suspension mtb and put 700x28 wheels on it. i had the same problem, going from V stop brakes to conventional

    That might be more of a challenge. Most older mountain bikes have cantilever or v-brakes. There are two mounting posts that serve as pivots for the brake arms. You would have to extent the mounting point for the brake pads on the brake arms themselves to make it work.

    I think the biggest challenge would be dealing with the travel and leverage issues. If you managed to mount the pads higher on the existing arms, you would have less leverage for braking. If you built longer arms, you could maintain the same leverage, but the brake lever travel would increase drastically.

    V-brakes have this "problem" and that is why you can't use v-brake levers with cantilever brakes and vice-versa. The manufacturers adjust for the difference in travel by making v-brake levers pull more cable than cantilever brake levers.

    I think I have written "lever" way too many times....

    True and good advice... so much for disc brakes, then, too.

    well you could get disc compatible MTB hubs laced to a 700c rim. I've seen it done quite a few times.

    Hmmm, food for thought. Thanks :)

    There are also 130mm disc hubs out there. They are hard to find, but they are available. You can also downsize some MTB hubs by changing out the spacers for thinner ones. You just have to be careful about not messing up the distance between the disc and the frame too much. If you start with a pre-built MTB wheel, you might have to re-dish the wheel to get it centered in the frame.

    You should take into account the spacing. the spacing is also slightlydifferent....a MTB has a rear axle spacing of 135mm where as aroad wheel has I think a 120mm spacing....front on a MTB is 110mm where as a road is 100mm I believe. You may be able to fit them in though.

    You are right about the spacing. If it is a steel frame, there is enough flexibility to fit larger hubs in small frames and vice-versa. If you like it well enough, a steel frame can be cold-set in order to keep the new spacing. You can find the technique all over the web (including Sheldon's site). Just don't try this with an aluminum frame. Moving the stays around on an aluminum frame can cause cracks.

    You are right about the spacing. If it is a steel frame, there is enough flexibility to fit larger hubs in small frames and vice-versa. If you like it well enough, a steel frame can be cold-set in order to keep the new spacing. You can find the technique all over the web (including Sheldon's site).

    while i don't know what the prices might be , Call on Coker Tire in Chattanooga TN and see if they can help you with the rubber part !

    Buchanan's can be reached via the web and can probably help with the rims

    5 replies

    The great thing about using 26" wheels is the availability of tires. Higher pressure "street" tires are available for mountain-bike rims just about everywhere!

    For those folks out there riding knobbies on the street - take heed! You don't have to sound like a mud truck when you are riding down the road!

    but,that's the only sound people hear when I'm riding my bike,unless I pedal backwards so they hear the loud clicking of my freehub. I liek the sound,

    Got a brand of those higher pressure tires you like? I am making an e-bike and I want to keep rolling resistance down as much as I can and I am going to be riding on pavement for 90% of the time.

    Maxxis hookworms.One of the best street tires with little rolling resistance.

    I know this is late as a late thing. But I love scwalbe marathons. They are armoured against punctures and run very smooth. If you're going for a bit watt ebike i would look at getting some fat franks