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Professional Crastinator
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Discussion Starter · #1 ·
I'd like other people to try this out and report back.

I hear it said that you should use "incompressible housing". This goes against that. A LOT.

But this simple mod makes my BB7 mechanical caliper feel like a hydro - and this is the prototype, using a hand-wound spring and a threaded barrel adjuster.

A good spring + a smooth barrel will = "supermodulation"
I gotta get down to the lathe.

Note the relative motion between the caliper and the barrel adjuster supported by the spring. The barrel adjuster simply slides in the hole - it is not threaded in. You need to watch at high quality to see the details.

This is on a 185mm rotor.

NOTES:
- The barrel adjuster should be under an inch long. The threads make the action less smooth.
- The spring is 1/2" long free length, and requires about 4# to displace 3mm.
- When the spring compresses, the barrel should bottom out before the spring is completely squeezed to its solid length; maybe 3mm of movement.
- This modification does increase the lever pull distance by a tiny bit, so minimize any extra play.

If someone packages this and markets it, don't forget where it came from.


-F

PS - I am posting this on the General forum as well because I think it's awesome.
 

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Discussion Starter · #3 ·
My BB7's modulate just fine stock. I'm not sure why anyone would want to add this much complexity to anything as simple and reliable as a set of BB7's.
Spring = "complexity"?

You can run larger rotors for more power without the "digital" or "grabby" feel normally associated with BB7's.

-F
 

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I don't get the point of this mod either. My BB7's also modulate fine & aren't "grabby" or "digital" (whatever the heck that means in a brake context). Plus you are increasing the lever pull distance, I don't want that.
 

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Discussion Starter · #6 ·
Or find a set of Shimano M950 brake levers and spin the servowave adjuster about halfway in.
Good point.
Forgot to mention I am using SD-3 on one bike and SD-7 levers on another. They work great, but the mod makes it even better. The mod is on the bike with the SD-7's.

I am also using semi-metallic pads, not organics.

Someone had asked for a picture instead of a vid, so here you go. The threaded barrel has been replaced by a smooth barrel.

During assembly
Spoke Rim Bicycle accessory Bicycle part Bicycle wheel rim

(that is not a frayed cable - it's silicone lubricant)

Assembled
Bicycle accessory Bicycle wheel rim Bicycle part Bicycle Rim


I am comparing my modded BB7s (SD-7 lever, semi-metallic pads, one-piece 185mm Roundagon rotor) to Hope Tech M4's (Hope Tech lever, organic pads, floating/2-pc. 185mm Hope rotor). I own both, and mostly ride the bike with the Hopes.

-F

PS - here is a great resource for setting up the Avid BB7: Avid BB7 mini resource - How to set up the Avid BB7 to give you an idea where I started from.
 

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Good point.
Forgot to mention I am using SD-3 on one bike and SD-7 levers on another. They work great, but the mod makes it even better. The mod is on the bike with the SD-7's.
I also have the SD-7 levers which I've used in the past with my BB7 brakes. I found that I was running a bit low on lever throw when I had the dial spun to where the brakes modulated the way I wanted. The old Avid SD 3.0 levers were better but they were just too darn big unless I used them with gripshift, which I hate. Shimano's servowave levers take up cable fast and then "cam over" to the high leverage/better modulation position after the pads make contact with the rotor. I have to say that it's a bit of a pain getting the lever & brakes to flip into the high leverage position at the right time, too early and it runs out of lever throw, too late and the modulation/power curve gets really wonky. In the end it was too finicky for me, so I went to hydraulic brakes.
 

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I can't see how compressing a spring before the brake engages would make it work any better.

You basically have to pull the lever more before the brake engages.

If you like the feeling of more lever pull before the brake engages, you could just dial the pads out so they are further away from the rotor.
 

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Yeah!
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I think there is a bit of a misunderstanding about what it going on here...

The spring he's using requires more force to compress than is required to move the lever, so up until the pads touch the rotor, the spring he added remains uncompressed. As soon as the pads put pressure on the rotor, the force of the spring is overcome. As he continues moving the lever, the spring compresses, increasing the pressure applied to the rotor until it bottoms.

The result is pad pressure ramps slowly for the first however many degrees of lever pull, providing greater modulation initially, then regular performance once the spring is fully compressed.

Yes, this has been done, but not in an inconsistent method as this. Unfortunately, this type of design is finicky, and wear on the spring will quickly result in the spring compressing first. This is a super cheap way to make modulated brakes, but not a durable method.

Don't know about MTB, but road bike brake levers have had a modulating design since the early eighties, IIRC. Regular levers don't provide as much modulation as a spring design can, but there have been a few designs through the years that use secondary cams to provide additional initial modulation.

Of course, the whole idea of brakes, like many components, is you purchase better brakes, you get better modulation, and it's done properly with precision bearings in the lever, tighter clearances in the caliper, etc, so you don't have to settle for lower total braking power to get it.

Nice DIY, just beware of the compromises.
 

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This makes mechanical sense as described above but one feature of concern is the potential for actuation variabilitity. That is, this may work perfectly until one time you happen to be 20 miles from the car and some sand lodges in the modification and when you slightly hit the front brake going 30 MPH it responds stronger than expected and your face is split before you know what happened or even clip out.

The mechanics are cool, but disc brakes are so sensitive I've learned to dislike even servo-wave (M985 FTW) but especially any mechanism exposed to the raw environment such as this that sits between the lever and pad actuation.

This is cool, mods are interesting, and I rode BB7's for a few years on my HT. I just wouldn't ride this kind of modification backcountry due to safety issues. I'd hazard a guess that brakes might be the most important mechanism to keep tight to keep oneself out of the ER (if you are going fast on sketchy terrain) so I wouldn't mess with them.

This is cool for perhaps riding in the city just not critical terrain.
 
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