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Dura ace BR-7400 rear brake installation

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Dura ace BR-7400 rear brake installation

Old 03-07-21, 10:25 AM
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jonny7
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Dura ace BR-7400 rear brake installation

Hello all, I'm having a small issue trying to reinstall the rear brake on one of my CV bikes.

I removed and disassembled the brake to work a bit on the return spring, which I felt had lost its shape. Now I can't manage to install it back on the frame. When I screw the nut in, I reach a point where it wont screw in anymore and where applying excess force only results in rotating the pivot bolt and forcing the return spring exactly how I'd like to avoid to force it. I don't know if this make sense. Bottom line is: I'm not able to fully screw the brake in. There's a gap I can't get rid of and I'm wondering if I a dumbly missing something here. I'm pretty sure I am not missing a spacer, although this could seem like a possible solution.


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Old 03-07-21, 11:21 AM
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What I don't see is the toothed spacer/washer that usually is located between the caliper and the brake bridge face. The amount of nut that is not seating against the bridge is about the thickness of the toothed spacer. BTW my understanding is that the toothed spacer is to better keep the caliper from rotating on it's mounting bolt and thus become "un centered". Andy




I'll also add that the spring's coils are now hindering the access to the (13mm?) flats that are used to help center the caliper. I don't have a photographic memory so don't remember which way the spring should be installed, coils towards the caliper arms or towards the frame. If the ft brake is still unmolested that one might give more insight about the spring's arrangement.
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Old 03-07-21, 02:01 PM
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Thanks for the reply! I was wondering about whether or not I was missing this kind of spacer, since there is one on the front brake.

but Iíve zoomed in a old picture of the bike and it seems like there wasnít two spacers, just the one I have currently. Rather odd, maybe the zoom technique is not to be trusted


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Old 03-07-21, 02:32 PM
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Could it be you have the front brake on the rear? I'm seeing the brake shoes mounted backwards. That would explain the extra space.
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Old 03-07-21, 02:38 PM
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If you disassembled the caliper down to the central bolt, you likely backed it out of the nut on the front more thanit was originally. Thus, more exposed bolt on the back side.
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Old 03-07-21, 03:19 PM
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Originally Posted by Crankycrank View Post
Could it be you have the front brake on the rear? I'm seeing the brake shoes mounted backwards. That would explain the extra space.
Regardless of whether this is the front or rear caliper, those brake shoes are reversed. Swap them before riding and the pads come shooting off the front of the holders. Check the fronts, too. The closed end of the holder always goes to the front, the open end to the rear.

Besides notched brake bolt washers, shorter Allen nuts are available, too.
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Old 03-07-21, 04:38 PM
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Originally Posted by rccardr View Post
If you disassembled the caliper down to the central bolt, you likely backed it out of the nut on the front more thanit was originally. Thus, more exposed bolt on the back side.

Not able to do this with this design. This caliper has the "traditional" center bolt and spring holder style where the spring carrier is "one" with the center bolt. On one side of the spring holder the arms are adjusted for free movement via the two nuts on the outward end (much like Campy NR and millions of other calipers). The amount of center bolt on both ends, beyond the spring carrier, are fixed and not changeable.

More recent Shimano calipers are of a different design with the center bolt's outward end a fixed item and the spring carrier and a knurled lock nut are the adjusting elements. IMO a more hassle prone design but not rocket stuff either.

One other possibility is that the recessed nut for the back got somehow swapped with that of the front. These nuts are available in varying lengths too. But my first thought of the missing toothed spacer is the route I would first check into as it gets you two bennies. One in that the brake fits the frame properly and the other is that the caliper is now better held from rotating off center. Andy
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Old 03-07-21, 05:10 PM
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Iíve have BR-7400 brakes on my bike for over 30 years; bought new. The rear only has a spacer, which I believe is slightly knurled.

My guess is you might be using the attach nut from the front brake which might be longer and you are running out of threads to be able to tighten it.

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Old 03-07-21, 06:03 PM
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Originally Posted by 70sSanO View Post
My guess is you might be using the attach nut from the front brake which might be longer and you are running out of threads to be able to tighten it.
Originally Posted by Andrew R Stewart View Post
One other possibility is that the recessed nut for the back got somehow swapped with that of the front. These nuts are available in varying lengths too. But my first thought of the missing toothed spacer is the route I would first check into as it gets you two bennies. One in that the brake fits the frame properly and the other is that the caliper is now better held from rotating off center. Andy
Yes !! This was it. I had already checked this and the while the nuts are the same lenght, I had failed to notice that the rear one (which I had put in front) has no "bottom". It can be tighten as much as you want. I have no idea whether or not these are the original nuts but it does make a difference! Thanks a lot, I'm always amazed by the amount of insight concealed in these forums.

Originally Posted by oldbobcat View Post
Regardless of whether this is the front or rear caliper, those brake shoes are reversed. Swap them before riding and the pads come shooting off the front of the holders. Check the fronts, too. The closed end of the holder always goes to the front, the open end to the rear.
Doh! Fixed this.

Originally Posted by Andrew R Stewart View Post
I'll also add that the spring's coils are now hindering the access to the (13mm?) flats that are used to help center the caliper. I don't have a photographic memory so don't remember which way the spring should be installed, coils towards the caliper arms or towards the frame. If the ft brake is still unmolested that one might give more insight about the spring's arrangement.
I am not sure to understand what you mean. After verification, the spring is installed in the correct way. The coils are a bit asymetrical/uneven, yes, this is what caught my attention at first. Is this what you are pointing at?


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