Monday, February 9, 2015

Tandem From ... Part 2

Yesterday, I put up the post about the Actos Machine tandem build focused more on the drivetrain.  Besides the R601/R603 cranks, it got new Ultegra 6700 shifters and derailleurs and an XT 11-32 cassette.  The shifters were installed on a set of Ritchey WCS carbon bars.  The Ritchey WCS stem was fit to a quill stem adapter (1" threaded fork).  The rear bars are Fyxation time-trial style bars in 25.4 to fit the titanium adjustable stoker stem.  A SRAM red aero bar brake lever operates the cantilever drag brake.  The red color lever is a nice touch/match to the red King hubs and red vintage Salsa quick releases for wheels and seats.

Part 2 will mainly deal with the rear chainstay mounted WTB Speedmaster roller-cam brake.  During my work on the bike, a friend who used to work at the old Point Reyes Bikes, where the bike was originally sold and built, recalled having had plenty of issues with the rear brake when building it originally.  The one thing about the rear brake that stood out to me was that there was minimal clearance between the cam and the bb shell.  There was no cable guide.  The shift cable, originally, ran across the bb shell without a guide (there was a large thin washer between the drive side fixed cup and the bb shell.  I assumed this to be to keep the guide-less shift cable from migrating off the bb shell to the right.  Maybe this was okay with the previous drivetrain, but this new 10-speed set-up would need to be a bit more precise.  

I decided the rear shift cable needed a guide to keep the cable from moving across the shell.  I modified a Shimano guide by cutting off the front derailleur cable guide and thinning out the guide to make it as low-profile as possible and installed it as far to the right as it would fit to allow space for the cam.  

To address the issue of the cam hitting the bb shell when the brake was applied, I dug back into a bag of tricks I learned long ago.  Dug deep.  WTB roller cams use a stainless bushing that fits on the brake post.  Then the arm with the pressed-in bronze bushing slips over the bushing and rotates around the bushing.  The arms also have a Grease Guard™system where grease can be injected into the side of the arm and then runs around a groove on the stainless bushing, thereby greasing the pivot and making it rotate smoothly. 

Years ago, I recall needing to modify another WTB roller-cam by pressing the arm onto the bronze bushing in a different location.  When moving the arm on the bushing, you lose the ability to push fresh grease between the bushing and stainless pivot - unless you make a new groove.  Making a new groove requires relocating the bronze bushing first, redrilling the bronze bushing, and making a new groove in the stainless pivot.  Easy.  But slightly time consuming.  

The brake is in the stock position.  The hole in the side of the arm is where grease is injected.

The arm relocated on the bronze bushing - gaining critical clearance for the cam to pull.

Yeah, that's going to work nicely.

I drilled the hole through the bronze bushing with the stainless bushing in place to see where the new groove had to be located - see the tiny divot above the stock groove.

I used a hacksaw to cut a small, shallow groove around the circumference of the pivot to serve as a guide where a deeper groove had to be made.

A Dremel tool was (lightly) fixed into my vise with a small round grinding bit.

More detail of the Dremel grinder and where the groove will be.  This is before I cut the groove deeper.

The old groove and the new groove.

Brake all buttoned up.

Tools used to modify the brake.

With the rear derailleur cable guide installed.  The front derailleur cable runs around the bb shell through a piece of cable liner.

New clearance for the cam.

Arm clearance on the right side...

Arm clearance on the left side.

Brake arm in its new location on the bushing.

When the bike was originally built, the brake bridge must have been redrilled to lower it.  I didn't like the look of the second, unused hole, so the bridge got trimmed giving it a cleaner look.

All done!

(What's playing:  Gang of 4 I Fled)


Anonymous said...

Why didn't you just flip the bushing so the existing groove would be on the other end? It looks like the new groove was unnecessary.

blackmountaincycles said...

Good thought. The bushing is open on one end and closed on the other. There is only one way for it to fit on the brake boss.

alex a said...

No "real bike shop" will have the knowledge or patience to do this.
Excellent work!

Major said...

Wow, this is a load of impressive mechanical work. I am left scratching my head though...why?

The old drivetrain looks way better. If I wanted drop bars and integrated brake/shifter levers, you sure could have convinced me to go with Retro-shift (Gevenalle) or some NOS brifters that could work with the old drivetrain.

But hey, its not my bike.