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I bought a bike exactly like this one some time ago (bonvelo, a small company here in germany): bike

I wasn't really happy with the brakes so I decided to search for a good used ones. I found a good offer for the shimano 7800 BR and bought them.

I installed the front one without problems but the rear one is being a nightmare.

The problem: When I try to install the shimano brakes one pad reaches perfectly the rim but the other one (opposite side than the cable) does not reach the rim and collides with the rubber of the tire.

I can't find which model of brakes did the bike had, I can only see the brand written and it says promax. Here are some photos of the two brakes: Front brakes Back brakes

I can't see what is wrong with the new ones, that doesn't allow the right side to reach the rim, because the height of both seems to be the same. The width of the tyre (28) should not be the problem as the front one works perfectly There is a washer that was in the old brakes but does't make any difference for this problem if I put it or not.

To show better the problem. This is the bridge: Bridge

This is the probem where the brake pad collides with the tire: Brakepad collision

And here the brake pad reaches the rim if I have a little angle between the bridge and the brake, but I can tighten the brake in that position: Angle between brake and bridge

Is there anything I can do to install this brakes in this bike?

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    The black brake in your picture is long-reach as @ojs says. You can see that the arms are longer. This bike probably needs two different types of brakes if the new front one is OK that one might be short reach and the rear one has to be a long one.
    – Carel
    Commented Apr 14, 2018 at 8:08
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    Welcome to the site and thanks for posting such clear photos!
    – David Richerby
    Commented Apr 14, 2018 at 9:14
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    Another thought - if you dry fit the rear brake from the other side of the brake bridge, does the angle differ? The nut may not fit right, but this could show if your brake bridge is not at the correct angle.
    – Criggie ♦
    Commented Apr 14, 2018 at 9:36
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    @Criggie sorry I read that too late. I already installed back the old ones so I can not test it. In the future I'll try to get some brakes with longer reach, I think tektro R559 may be a good option, but as you already mentioned, the rear brake in the road is almost never used, so I'll leave it as it is while I change other things with more priority.
    – nck
    Commented Apr 14, 2018 at 19:25

2 Answers 2

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What you really need is brakes with longer reach. Reach is the measurement from mounting hole to rim, you can measure it with a measurement tape and it is listed for most of rim brakes.

If you absolutely want to install these brakes no matter the cost or reliability, there exists a component called drop bolt. These used to be more common in days of classic steel frames and single pivot brakes, but NOS parts are still available. I would recommend disassembling your brake and verifying its mounting bolt is compatible before buying anything.

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  • Thank you, for the answer. I've tried to find one of those pieces but they are too expensive compared what the brakes costed me... I've tried to measure the reach (mounting hole to rim) and it looks like something around 6cm. I'd like too keep the silver asthetics of my brakes and the only thing I've found not too expensive are the campagnolo potenza, but I can't find in any shop that this measure is given when they sell the brakes.
    – nck
    Commented Apr 14, 2018 at 10:54
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    A quick search showed that all Campagnolo brakes are short reach. Search for medium reach. 60mm sounds quite a lot for what the old brakes look like, the measurement should be taken center to center.
    – ojs
    Commented Apr 14, 2018 at 12:46
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I had this exact problem - fitted some long-reach dual pivot calipers because the bike was going from 27" to 700c wheels.

The front wheel was perfect and just bolted on in.

The rear caliper STILL wouldn't reach the rear wheel brake track. I checked with a ruler, it was definitely long-reach but off by ~4mm.

So I made a drop plate from some scrap aluminium and two bolts.

https://criggie.org.nz/pictures/bikes/raleigh_arena/rear-brake-mount/20180120_123327.jpg Own work

This specific plate style won't work on your brake bridge, but you might be able to fit a sandwich of two plates either side of the bridge and have the brake's bolt go through both.

If worst comes to worst, just reinstall the original rear brake caliper and live with it. The front brake does most of the work anyway, so having the good brake there is what counts.

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    Steel would’ve been better for the bracket than aluminum. The bracket will bend slightly every time you brake and then return. Eventually you’ll get metal failure. It might be in 100 years or 10 years or 1 year. Fortunately the worst case is that the brake will jam in your rear wheel and you’ll skid out. Utterly survivable.
    – RoboKaren
    Commented Apr 14, 2018 at 15:37
  • @RoboKaren agreed, but its what was available at the time. And its decently thick. It is an area I definitely inspect on my periodic maintenance.
    – Criggie ♦
    Commented Apr 15, 2018 at 5:41
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    Sheldon Brown's site also discusses home made drop bolts. All the examples there use aluminum. Whole frames and the brake calipers themselves are made of the stuff, so it's not an unreasonable choice if sized and mounted appropriately. sheldonbrown.com/home-drop.html sheldonbrown.com/calipers.html
    – remcycles
    Commented Jun 10, 2023 at 23:14
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    Of course, metal fatigue is real and I'm not a mechanical engineer, so I can't say what "sized and mounted appropriately" is for any particular situation.
    – remcycles
    Commented Jun 10, 2023 at 23:47
  • @remcycles good point - yes I'd rather overbuild a brake than underbuild.
    – Criggie ♦
    Commented Jun 11, 2023 at 1:53

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