Webmaster note:  Many thanks to Bryan for putting together such an excellent resource and for his permission to post his work on this site. 

It seems a number of people this year have asked if it was possible to install an Avid disc brake on a Santana tandem, and for information on how to do it.

Let me start by first thanking Brian Jensen for his assistance with the Avid Disc brake install.

Next, I put together these photos along with a few words in the hope that this helps a few fellow riders with their quest.

Gotcha #1 - Mounting the caliper to the bike:

Which caliper?
Use the Avid Road caliper for Road style brake levers, or the Mtb caliper for Mtb brake levers. The only difference between the two, is the "throw arm" (otherwise called an actuator). Since road levers don't pull as much cable as Mtb levers, this is why they make a different caliper. However, you could probably still use the Mtb version with your road levers, if you add an inline assist component like a Travel Agent or Brake Power Booster. You'll just have to decide how you will run the cable and where you would put one of these boosters.

As a side note, I have a Road bike tandem so these instructions are geared toward that implementation.

Using a standard Avid Mechanical Disc FRONT ROAD caliper, simply mount it to the Hayes-International Standard adapter provided by Santana. The adapter (the silver "U" shaped thing attached directly to the bike frame) has plenty of adjustment capability built into the base/frame mount point and at the caliper mount point. It comes with the two hex screws too. Why the FRONT Avid caliper? Both the front and back Avid disc calipers are identical, except for the black mounting adapter supplied by Avid. The front adapter brings the caliper closer to the frame, which when mounted onto Santana's adapter, puts the caliper over the rotor/disc in the correct position. When you are ordering a complete kit, order an Avid Mechanical Road Front, then mount it on the back of your Santana tandem.

Now the trick for road bikes is that Avid does not package a 203mm disc rotor with their Road calipers and of course, it's the 203mm that you want. Only the MTB downhill kit comes with a rotor this size, so you end up having to order the 203mm rotor separately from the Front Road kit. The Avid Road kit comes with a caliper, the black IS adapter with mounting screws, a 160mm rotor and the CPS (caliper positioning system) set of washers. Brake pads and red adjustment knobs are already installed. As I mentioned, you can get a Mtb DH kit complete with the 203mm rotor, which is the cheapest option if that is the kit you want (for road bikes just add one of the cable boosters mentioned above).

An easy source for the Santana Hayes-IS adapter and the other components you need is Mark Johnson at Precision Tandems. Mark has put together a complete Avid disc kit for Santana owners.

Gotcha #2 - cable routing:

The standard mount point for the rear caliper is on the seat stay, however, Santana puts theirs on the chain stay. The later is probably better technically, because when a disc brake is applied the rear wheel is forced up into the dropouts (this is a good thing). Conversely, when the mount point is on the seat stay, braking forces combined with wheel/road traction try to kick the wheel down and out of the rear dropout (a bad thing). So why is the seat sstay the standard? Because it's the easiest for manufacturers to provide space for. With all these new and weird rear suspension configurations, some bikes don't even have a chainstay.

The issue is this, when mounted on a Santana, the cable comes out of the Avid caliper pointing downward which prevents running the cable up the seat stay as most disc brake equipped bikes do.

For cable routing you have a couple options:
1 - If you have a cable stop on your stoker's top tube, you can route the cable in a big "S" up there, and you're all set.
2 - If you have hydraulic cable guides supplied by Santana, don't sweat it, just follow the same route they provided. However, we'll have to do a little work on the underside of the bike to provide a cable housing stop.

Gotcha #3 - providing a cable stop:

Ok, with this dual bottom tubed frame you could slap on an aftermarket cable stop. But who wants to add a chunky piece of hardware to their bike? Not me. Come a little elbow grease and even less skill... using a file and drill.

My quick solution:

Note on the right side of the hydraulic guide, how sloped the entry point is. Now look on the left side and you will see that I filed the shoulder flat at a 90 degree angle. This is to provide a flat mating surface for the cable housing end to rest against. Whew, anyone got a smoke?

Next, we find a cable housing end that will suit our purpose. In this case, I found that along with the silver braided housing (outer layer is braided, inner is coiled and then Teflon sleeved) I bought from Quality Bicycle Products, they provided a package of step-down ferrules (fancy name for cable ends). The benefit of the step-down, is that it provides a nice ridge in the ferrule which I used as a stop point.

Ok, the inside walls of the hydraulic guide were straight edged, meaning, I had to drill out the guide very slightly to accept the round ferrule end.

One last and slightly kludgie item... the zip-tie. Well, I'm a bit leery of the cable slipping out of the modified guide, so I added a zip-tie to ensure the cable end stays in place.

The clean way:

If you have an S&S bike, send your bottom tube to Santana and have them swap the hydraulic guide for a standard cable stop. In my case with an aluminum frame, the guides are simply riveted on, and they can pop on a new guide very easily.

Inner shot out :^)

By this time you might be asking "What the heck is that spring doing there over the inner cable?".

Even before mounting this system, I had heard that the return spring tension on the caliper didn't pull all that hard. As a result you might have to run a fairly slack cable tension. I phoned Avid and inquired about a possible solution (at least a stiffer spring) but to no avail, although they did sort of admit the cable pull tension was marginal.

Enter the additional expansion spring and a couple cable donuts at either end. I'm calling this: B[ryan's] A[vid] S[pring] T[ension] A[ssist] R[etrofit] D[evice], otherwise known as the BASTARD solution.

Webmaster note:  The picture above and the description below have been updated resultant of an internet post made by Brian.  We are pleased to pass it on. 

If you desire a firmer brake lever feel, here's my latest "helper spring" for the Avid disc caliper. Get a package of 1/4" x 1" compression springs at Home Depot for about $1.50 then snip one to 3/4" long. Get a small washer and put an "S" bend in it to keep the spring from creeping over the caliper arm. Install as per photo... 

 Presto, much more back pressure on the caliper arm and increased ability to tighten the brake cable (remove slack). It looks simple, because it is.

Last but not least, a typical barrel adjuster at the head end.

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