Avid Disc Conversion Complete

[TandemGeek]

As many teams have done over the past few years, we have had our tandem retrofitted to accomodate an Avid BB7 (Road) rear disc brake as our primary rear braking device.

http://www.bikeforums.net/attachment.php?attachmentid=40493&d=1174845442

Our travel tandem previously had a Campy dual pivot rear rim brake and accommodations for a Hope mechanical disc drag brake as needed for mountainous tours. Given that we never had the rear disc on the tandem except when needed -- and then occasionally found ourselves in unfamiliar territory where we wish we did -- we have opted for the best of both worlds in rear brake control by fitting the Avid BB7 203mm rear mechanical disc as our primary rear brake, operated off of my right Ergo brake lever.

Our builder, Glenn Erickson, removed the custom braze-ons originally fitted for the Hope mechanical disc and installed new ones that work with his new Avid BB7 caliper mount. Via his custom installation, the disc caliper remains within the confines of the rear triangle, taking advantage of the strength of both stays as well as creating an aesthetically pleasing installation.

Given that we did not want to change out our Phil Wood hubset for a dedicated disc hubset, excess material was machined off a thread-on 6 bolt disc rotor adapter so that the rotor would be properly aligned with the disc caliper.

The job was topped off with a repaint of the left rear stays.

Instead of using a 1/4" x 1" spring shortened to 3/4" as a "booster" for the Avid's return action, I found that a 5/16" x 3/4" had a better fit and did not require the use of any washers to preclude the spring from travelling up the return arm. Interestingly enough, the spring I selected came from an assortment pack sold at Home Depot for just under $4. As others have noted, e.g., Bryan Boldt, et al, the additional spring provides a more positive lever feel than the stock Avid BB7's spring.

Although our rear brake isn't broken in by a long-shot, it is already demonstrating better modulation and braking power than our rim brakes. While originally somewhat less than warm to the aesthetics of the rear disc installation, with the rear brake removed it's actually a fairly nice looking installation, all said and done.

We'll report on its performance as we log begin to log some miles where it could be pressed into service. What we've found interesting thus far in the two or three shake down rides that we've taken with the Avid is that we really don't use our brakes all that much... and Debbie is none to happy when I apply the rear brake "for testing purposes" on some of her more enjoyable descents.

[Lost Coyote]

Nicely done. I love the caliper mount esp. the location between the stays. Now you just need put a disc up front where it will do the most good....... here fishy, fishy, fishy.

[TandemGeek]

Nicely done. I love the caliper mount esp. the location between the stays. Now you just need put a disc up front where it will do the most good....... here fishy, fishy, fishy.

We'll see how the rear brake works out for a year or so and then perhaps we'll extend our experimentation to the front-end, perhaps....

[phinney]

I've been running those for about a year now (front too) with no ill effects. The first few rides they were on the weak side but are much better now - just needed some "braking" in. I played around with a helper spring on the back at first but ended up taking it off, seems to work fine without it. I haven't had to adjust them in a long time.

[TandemGeek]

I've been running those for about a year now (front too) with no ill effects...

'04 Cannondale RT1000? I recall that you one time posted about your conversation with Mike at SRAM regarding any customer reports of melting the red plastic adjuster knobs but never confirmed that you were riding a dual-disc C'dale.

I found that the helper spring removes the slack in the very long brake cable run, takes the static cable load off the Avid BB7's internal spring, and firms up the lever response quite nicely. It took me about 4 different spring set-ups to find the right balance and fit but this one seems like a keeper.

All in all, I'm pretty optimistic about the set-up; worth the wait.

[George Handy]

Very nice! Much cleaner looking than the usual 'behind the seatstay' caliper location. Looks like you coule still mount fenders or rack without any problem.

[TandemGeek]

Very nice! Much cleaner looking than the usual 'behind the seatstay' caliper location. Looks like you coule still mount fenders or rack without any problem.

Thanks and yes, the placement does permit rack and mud guard installation without disc brake interference issues. Glenn has always done an exceptional job of blending form with function and when he started installing mech. drag discs on his custom tandems back in the mid-90's he began installing the Hope mech. disc calipers in the stays.

I'd actually contacted a local frame shop to see if they'd be willing to make the mod but with the stipulation that the Avid had to remain in between the rear stays, same as the original Hope disc. However, after seeing the photos of the stays, the assessment was "impossible to do". So, while I didn't want to bother him with it, I ended up shipping the frame off to Glenn in Seattle a few weeks ago. As usual, his workmanship is flawless and his painter did a perfect job of blending in the touch-up with the original paint.

[phinney]

'04 Cannondale RT1000? I recall that you one time posted about your conversation with Mike at SRAM regarding any customer reports of melting the red plastic adjuster knobs but never confirmed that you were riding a dual-disc C'dale.

I found that the helper spring removes the slack in the very long brake cable run, takes the static cable load off the Avid BB7's internal spring, and firms up the lever response quite nicely. It took me about 4 different spring set-ups to find the right balance and fit but this one seems like a keeper.

All in all, I'm pretty optimistic about the set-up; worth the wait.

That's me. Mike said he'd never heard of the melting knobs and if I ever had it happen to send him the brake and he'd replace it immediately. I was hoping to get back to the mountains this year and see if I could melt one.

The cable slack bothered me too so I did the spring mod at first, I probably have the same spring kit you do. I kept fiddling with it and either the spring didn't fit quite right or the lever would feel too stiff out on the road. Finally I just tried it with no spring at all and, surprisingly, the slack doesn't seem to be an issue.

I did add some of those in-line brake levers on a whim. They have much more cable travel than the normal levers. I don't use them much but they have plenty of leverage and are less mushy. I wish the regular levers felt as good. The in-lines are in a handy position to hold the bike when stopped.

I put some bigger tires on for added stability on dirt roads and now there isn't sufficient fender clearance in the front. I'm contemplating removing a little material from the fork!!

Also added one of those two legged kickstands. We trailer all the time and the stand is a great convenience.

[wsurfn]

All Right Tandem Geek.

What would one have to pay to get The craftsman to do that job?

Mark

[TandemGeek]

What would one have to pay to get The craftsman to do that job?

Well, that kinda depends... First off, I'm pretty sure that Glenn only works on and occasionally builds his own frames these days so you'd have to get your hands on a Erickson tandem. Seriously, it really depends on a lot of things.

For some of his tandems that were built with the Hope disc braze-ons allow the new Avid bracket to bolt right up without any frame work and have hubs that are fully compatible with the 6 bolt discs, you're talking about the cost of the brake, the custom bracket, and a little bit of Glenn's time to fine-tune the installation.

Then, there are somewhat unusual frames like ours which is very small and which required everything but a new hub and wheel rebuild. The frame work was time and material, paint was time and material (noting that small jobs are't necessarily inexpensive given that there's still the same set-up and clean-up activity associated with painting something even as small as a stem), the cost of the new brake & rotor, and then the custom machining of the thread-on disc adapter for a total cost a bit under $400 not including insured shipping to and from Seattle.

For reference purposes, that's a lot less than a carbon fork, new high-zoot crossover crankset, or a new rear wheel for what is primarily (2/3) the time and talents of three craftsman who are all sole proprietor businesses. To me, that's a great deal.